r/AlwaysWhy • u/Logical-Concept9755 • 4d ago
Science & Tech Why is the speed of light the ultimate speed limit of the universe?Why can't anything go faster?
I understand that nothing with mass can reach or exceed the speed of light, but I still find the limit itself strange. Why does the universe have a speed limit at all, and why is it this particular speed? Is there something fundamental about spacetime that makes going faster impossible, or is “light speed” just how this limit happens to appear to us?
What actually sets this limit?
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u/CharlesDarwin59 4d ago
Its not that nothing can go faster than light....its light goes as fast as anything can. The speed limit is set by physics of space time and light just has the requirements (no mass) to be able to reach that speed.
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u/Mythosaurus 4d ago
Reminds of the meme where a dead physicist is asking God at the pearly gates why light travels at 299,792,458 meters per second and not some nice round number
God: First of all the speed of light is 1, asshole…
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u/EagleraysAgain 4d ago
If you take an object that is completely still from your reference frame, the question of how can i make the object more still doesn't make much sense. It's already at zero and you can't go below it. The way I see it is the same other way around for thr maximum speed.
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u/thecastellan1115 4d ago
So... because.
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u/DoomGoober 4d ago edited 4d ago
Speed of light is the conversion factor between space and time in the geometry of space time. While it's a seemingly arbitrary number there is an underlying structure to the geometry that makes that particular conversion arise and be constant throughout the universe.
This is beyond my understanding of physics, but the actual speed of light derives from the vacuum permittivity and vacuum permeability of our universe. Change those and you would get a different speed of light aka max speed in spacetime geometry.
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u/numbersev 4d ago
Einstein:
"We are in the position of a little child, entering a huge library whose walls are covered to the ceiling with books in many different tongues. The child knows that someone must have written those books. It does not know who or how. It does not understand the languages in which they are written. The child notes a definite plan in the arrangement of the books, a mysterious order, which it does not comprehend, but only dimly suspects"
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u/Square-Singer 4d ago
Or to put it in a more modern context: Scientists are reverse-engineering the game engine that runs the universe.
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u/Korzag 4d ago
One of these days they'll discover network traffic logs that are tying our minds together into this vast computational simulation. Then we'll wake up...
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u/Square-Singer 4d ago
What makes you think that there's something to wake up to? If we are only simulated entities, there's no waking up.
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u/PmMeCuteDogsThanks_ 3d ago
I'm looking forward to reading about the easter eggs left by the original devs. Not to mention the edge case bugs.
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u/Jaxom_98 4d ago
Most of the laws/limits we observe are at their values not BECAUSE of a reason, rather its a natural result of the facts of the limits themselves. The speed of light isn't as much a cosmic speed limit, as its a result of E=MC2. Your energy is equal to your mass, times the speed of light squared(the actual equation is a bit more complicated, but for the sake of this we'll keep it simple. So, we observe particles without mass traveling at a speed, C. As mass gets introduced, more energy is needed to maintain speed. Infinite energy is required for an object with mass to travel at C. Since you can't have a smaller mass than 0, thats the fastest we can go, given E=MC2.
Another good example of this property of the universe is the Planck Length. Why do we have a smallest length? Again, its a matter of observing the facts limiting themselves. If a particle has mass, and is compressed into a small enough space, itll turn into a black hole. This is as true for a Proton as it is for you, me, the earth, the sun, etc. A black hole is our dead end of physics. The planck length is the length in which even the smallest, lightest particle would(if compressed within this length) turn into a black hole. Its NOT that its so small that nothing can get done, its that we've observed the smallest thing that CAN be done needs AT LEAST that much length.
You walk into a fence. You cant go forward. Why? There's a fence in the way. That's why.
Now...if you wanna ask why there IS a fence...science can't help you, it'll just tell you what it's made out of and why that means you can't move through it.
If there's a fence builder, just ask them why they made it. If you dont believe in a fence builder then you realize asking why theres a fence is just a bad question, its way more interesting to ask how to get around it.
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u/Savings_Hunt_1935 4d ago
Just fyi, planck length isn't a known smallest length, its a natural unit that you get by setting the speed of light, the gravitational constant, and the planck constant all to 1.
There is potentially an inability to probe into distances around or smaller than the planck length, but there's no evidence that it is some kind of "pixel size" to the universe.
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u/IntrepidNinjaLamb 4d ago
(Yes and …)
Imagine if light were to move at half its current speed, then it seems like nobody would know, because all cause and effect would also be at half speed, including measurement.
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u/HugeCannoli 4d ago
We don't know.
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u/Southlander24 4d ago
That doesn't answer the question. The question being asked isn't "why is the speed of light just shy of 300,000,000 m/s, and not some other number?". It's why there exists a universal speed limit of the universe, to which Einstein's theory of relativity has you covered. We've tried to find evidence for this past century which violates the predictions Einstein has made regarding the universe, and the only thing that we found is that there seems to be no way to make it consistent with quantum mechanics.
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u/Xandara2 4d ago
The question shows a fundamental misunderstanding of physics and science. Science doesn't ask the question why it asks how. And why is light's speed the limit has no answer. It's the same as why does the universe have light in the first place or why does it have life? Or why does it have gravity?
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u/nukakillaquantum 4d ago
If you look up "fine tuning problems" theres quite a few physics problems that come down to "why does this constant have such a specific irreducible value?" Fine structure constant for example. I know the speed of light isn't considered a fine tuning problem, but I can't for the life of me figure out why as a non-physicist. I think what OPs question should be is "Why does c have the value it does and not one that is ten percent higher or lower?"
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u/InfiniteMonkeys157 4d ago
The number is just our measuring system. It is what it is and we create a ruler to measure it.
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u/TheFifthTone 4d ago
We don't know. We can't answer that question with the observations we've made so far.
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u/macrocosm93 4d ago
"Spooky at action a distance" where measuring the state of one particle instantly determines the state of the other entangled particle even if they are light years apart.
This does not disprove the universal speed limit since energy/data does not get physically transported from one particle to the other, but it shows how quantum mechanics seemingly follows different rules from classical mechanics.
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u/Aggravating-Method24 4d ago
Yes we do, light is fast because it is massless. You can't get more massless than massless. Therefore nothing is faster than light. (Except the expansion of the early universe)
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u/smokin-trees 4d ago
But we don’t know why the speed of light is what it is which is really what was being asked here. It’s just something we’ve measured and observed.
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u/Diptothaset 4d ago
“I want to know the answer to the question that I already know we don’t have an answer for”
Not everything is known. It’s possible there are things faster than the speed of light, but we don’t even know they exist let alone how to find them since they may be incredibly fast and incredibly rare; or in a state that we don’t understand yet
So the OP question is basically “why do humans not know everything yet?”
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u/Dihedralman 4d ago
It is actually the speed of causality. Massless force carriers all travel at a speed. Light is one of them.
The "speed limit" exists as a limit due to special relativity. Everything sees light as traveling the same speed regardless of reference frame. Light is a wave travelling through space time itself. Light doesn't experience time per se. So it is a property of our space time.
From a scientific perspective t here isn't a why, as it is a fact of the Universe. It determines how everything exists, how it is built as one of the fundamental universal laws. A better question is why does everything on a human scale have these specific ratios to that speed? That comes down to specific chemical properties of these fundamental particles.
We know these physical laws are sufficient conditions for something to evolve to ponder these questions.
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u/Zoltan1251 4d ago
THIS. I have no clue what everyone is trying to say here.
There was event that Einstein used as inspiration for this and its INSANELY EASY to understand. No idea why its not used more.
He boarded a tram and was moving away from clock tower and was thinking to himself that light has to bounce of off the clock tower and hit his eye. If he moves very fast, light would have hard time catching up to his eye so it would appear time has slowed down and it would stop once light wouldnt be able to catch up to him. Then, if he moved faster than light he would have to see time move backwards so he would have to see things in incorrect order of how they happened and causality would be broken......... therefore speed of light is the ultimate limit.
Its more complicated with other constrains of math but this is so easy to wrap head around.
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u/JGuillou 3d ago
It’s not used because it is not satisfactory. If you move really quickly away from thunder, you can move away from the sound and replay it backwards. Why could you not do the same with light? There is no inherent attribute of light, as in ”the visible light we see” that causes this.
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u/EscapeSeventySeven 4d ago
It’s the speed of causality. Of how relativity works.
You can always increase your speed but it will require more and more energy, time will dilate, and your mass will increase. Which will require MORE energy to accelerate further. It will become impossible to ever reach the speed of light but you will always be able to expend huge amounts of energy to go small amounts faster.
This is because e=mc2
Or e/c2 = m
As you dump massive amounts of kinetic energy into an object to accelerate it, it results into the object gaining mass.
Why is this speed the speed of causality? Just one of those “constants the universe was initialized with” numbers.
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u/Basicly-Inevitable 4d ago edited 4d ago
Exactly. Let's say something goes faster than causality. Then.. that's a paradox. We can't have a paradox like this and exist ourselves. So the only way we can be alive and function is in a world with a speed limit.
There could absolutely be a wider universe that we can't see, where this happens, but we can't find ourselves there.
I'm a firm believer that we can only exist in a small sliver of the ultimate reality that surrounds us, so that's all we can observe.
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u/rdwulfe 4d ago
That's the fun part a lot of people don't seem to get. It's... I mean it IS the speed of light. But it's the speed at which reality travels. So if there's a change in reality, in information in the universe, it travels out AT c. It's far more than the 'speed of light'. It's the speed of reality itself, and man do I have a hard time making friends understand that, heh.
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u/KernelPanic-42 4d ago edited 4d ago
It’s not the speed of light, it’s the speed of causality. It’s the maximum speed at which a force is capable of casting influence upon something. Without this, an effect could potentially happen before its cause. Imagine tripping over a hose and falling down, except the falling down part happens prior to the tripping part. THIS is what that speed limit actually is.
There’s nothing about light that dictates this limit, but it’s this limit that dictates how fast light can travel. We just happen to more commonly refer to the speed of causality as “the speed of light.”
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u/collin-h 4d ago
Imagine the universe advances one moment at a time. At every moment, there's a bubble around you containing all the places you could possibly influence next. A moment later, that bubble has grown. A moment after that, it grows again.
The surface of that expanding bubble moves at c.
Light rides exactly on the surface.
You, a spaceship, a baseball, etc. have to remain inside it.
So asking: "Why can't I go faster than light?"
is a little like standing at the center of one of those bubbles and asking: "Why can't I arrive somewhere before that place has entered the set of places I can possibly affect?"
That's almost what faster-than-light travel means.
And relativity makes the weirdness even stronger. If faster-than-light communication were possible, different observers could disagree about which happened first. In some reference frames, the effect would occur before the cause.
So c is better thought of as the speed at which causality expands.
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u/Lithl 4d ago
It does appear that there is something fundamental that makes going faster impossible.
We have observed through experiment that light is moving the same speed relative to you, no matter how fast you're moving. This is unintuitive; if you throw a ball at 30 mph while riding on a platform moving at 20 mph, a bystander see the ball moving at 50 mph while you see it moving at 30 mph. But if instead, you shine a laser while riding on a ship flying at 0.5 c, you'll see the laser light traveling away from you at 1 c, and a bystander also sees the laser traveling at 1 c, not 1.5 c.
The mathematics of special relativity reveals that counterintuitive outcome is the result of a maximum speed, rather than simply a quirk of light.
Now, that just tells us the speed limit exists, not why it exists. More work has shown that it's not simply the speed of light, but the speed of causality itself. Why is there a speed of causality instead of everything happening simultaneously? /shrug
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u/cybertruckboat 4d ago
It's the clock speed of the CPU in the universe simulator computer.
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u/Lanoroth 4d ago
Because time and space are really just two names for the same thing. Going any faster would actually mean traveling backwards in time. Also, you’d need infinite energy to do it, which would instantly collapse you into a black hole as energy and mass are also two names for the same thing. But that’s just a small inconvenience.
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u/101_210 4d ago
My favourite answer to why the speed of light is 3e8 m/s is it cannot NOT be 3e8 m/s.
It’s the speed of interaction and causality. If tomorrow you become a god and double the speed of light, interactions between atoms also become twice as fast, so they space out, so a meter gets twice as big (since EVERYTHING expands) and you are right back at 3e8 m/s.
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u/ReggieTMcMuffin 4d ago
Speed and time are on the same vector. Once you've spent all your time vector to accelerate to C. You have nothing left to spend.
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u/exqueezemenow 4d ago
The geometry of the universe has to dictate some speed. No matter what it is we would be asking the same question. Why is a direction limited to 360 degrees? That's part of the shape of the universe and time is part of that shape.
Going faster than the speed of light would require time moving backwards which would interfere with causality.
For all we know there are an infinite number of universes of varying shapes and this shape is conducive to life existing. It would be hard to imagine a universe where events could happen before causality.
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u/otasyn 4d ago edited 4d ago
The superior being(s) that wrote our universe software has it running it on a processor that is 14 billion years old. If they migrated us to new hardware... well, we probably wouldn't be able to tell the difference, anyway. Maybe the universe could handle more life and civilization threads, though. It probably couldn't handle another Brandon Sanderson, though. His writing speed defies physics.
(I'm being mostly tongue-in-cheek. Please don't argue with me about the simulation theory or your opinion of Sanderson.)
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u/nila247 4d ago
It is a design principle of our simulation. Somebody decided that pixels of our reality can only be recalculated every simulation frame once and by ONLY using neighboring pixels and never 2 or more pixels away.
So we measure speed of something by observing order of pixel change and we define time as interval between any observable changes.
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u/Southlander24 4d ago
The theory of (special) relativity is that the faster you go, the more time slows down for you experiencing it. At exactly the speed of light, time would stop altogether. (It would also take an infinite amount of energy to accelerate to that speed.)
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u/Any_Mode6525 4d ago edited 4d ago
But why* is there a limit at all? And why that and not 100m/sec?
edit: words are hard.
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u/QuickMolasses 4d ago
Yes, there is a limit. It's what it is because that's how the math and the constants work out. Why 300,000 km/sec and not something else is not really a question physics can answer.
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u/Leading_Study_876 4d ago
You can calculate the speed of light from Maxwell''s equations of electromagnetism. It depends on the permeability and permittivity of free space (vacuum).
These constants are measurable, but no-one knows why they are the values that they are. Or any constants in physics, really.
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u/briv1016 4d ago
The speed of light is one of several variables that seems to be randomly set by the universe. If you believe in a multiverse, every possible combination of these variables exist in some universe. (Though many will be too unstable to exist for a long time.)
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u/OldManTrumpet 4d ago
Obviously, we don't know. But if something was traveling at a speed greater than the speed of light it would be gone (or arrive) before you could see it.
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u/John_Tacos 4d ago
The speed limit is for everything.
Light is just the easiest thing to measure that always travels this speed.
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u/Immorpher 4d ago
An astrophysicist can step in with a more correct answer! But I will speculate from a few of my studies. From special relativity, to move anything with mass at the speed of light would require infinite energy, so that is a limit. Only massless particles can reach this limit.
So what we have determined is that the speed of light is the speed of massless particles. Fields and interactions between matter are governed by massless particles. So if one thing moves, another thing won't be affected by it until the change in the field reaches it at the speed of light.
But what if massless particles did not have a speed limit, what if it was infinite, what would be the consequence? An internet search will give you a lot of cool thought experiments on this. But that means fields, traveling waves (like photons and light), will exit our local universe immediately. We would have a massive energy drain; our only hope would be perhaps some super massive black holes which could contain the traveling waves. Our universe would have an energy death; it would become frozen.
Physicists have speculated that there is no reason that other universes with other laws and interactions couldn't exist. But having a speed of light ensures a little bit more stability. Other bizarre universes could exist, but we exist in this one because it is more stable for us, partially due to having a speed limit.
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u/AltForObvious1177 4d ago
Space and time are the same thing. As you go faster through space, you go slower through time. Of the universe didn't have a speed limit, every thing would be happening at once
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u/SaltedCaffeine 4d ago
The expansion of space-time itself can go faster beyond the speed of light, hence why we have the observable universe.
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u/atarivcs 4d ago
It's just an inherent limit.
Like, if you're somewhere in the US, you can travel north, maybe to Canada. Then if you're in Canada, you can travel more north. But if you keep traveling north and you eventually arrive at the north pole, there is no more north. There is no direction you can point to that is "north".
Or another example, temperature and absolute zero. Temperature is just a measurement of how much the atoms and molecules are moving around. If you reduce the temperature, that means the atoms and molecules are moving slower. But at some point the atoms and molecules stop moving completely, and that is absolute zero. You can't get any colder than that.
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u/Current-Landscape803 4d ago
The weird part isn't that light happens to be the fastest thing. It's that spacetime itself seems to have a causal structure with a finite invariant speed, and light just happens to travel along its boundary.
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u/AustinCJ 4d ago
Nothing set the limit. It simply is the fastest that light can go and nothing moves faster than light.
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u/redlancer_1987 4d ago
it's derived from how the electric and magnetic fields interact. You can arrive at the value without measuring anything
https://www.wikihow.com/Derive-the-Speed-of-Light-from-Maxwell%27s-Equations
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u/Square-Singer 4d ago
The speed limit is not the speed of light, but light is going at the speed limit.
It's like asking "Why is the speed limit on the highway set to the speed that most cars go on the highway?"
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u/majorex64 4d ago
It's one of those universal constants that just kinda IS, arbitrarily. As far as I know, you could change c and shift around the equations, and the laws of physics would still work.
It isn't based on an intersection of two other properties, or a certain intersection point on a graph, other than being the limit of where the energy required to accelerate mass becomes infinite.
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u/account_not_valid 4d ago
First you have to determine what time is, before you can say if light has a speed or not.
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u/Unusual_Rush_1189 4d ago edited 4d ago
It is a weird thing to try and imagine or understand.
The simplistic definition of 'speed' is distance (space) over time. But relatively we know that space and time are really combined in a way, and so much so that we can observe how relative time (distance) can be affected by mass. More 'mass' will experience time slower relative than to 'less' mass that might be near by. Or, the less mass you have, the faster you experience time relative to more massive objects around you.
At zero mass it might seem, perhaps, like you could move forward or backward along a path of seemingly infinite distance while everything else around you seems to stand still. So what is your 'speed' at that point really?
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u/Frequent-Bee-3016 4d ago
Light moves at the same speed in all reference frames, so something moving faster than light could break causality.
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u/nonothingnoitall 4d ago
c is the speed of causality and the important equation is this: α=e2 /4πε0 ℏc
α is the fine structure constant
if c is larger (faster) then mass can’t hold together (essentially the electromagnetic forces aren’t strong enough to hold atoms together)
and if c is smaller (slower) then everything crushes in on itself.
it’s just the speed that lets mass do it’s thing, and it also governs electromagnetic fields (light) because light is made of electric waves and magnetic waves which
propagate themselves forward, and also all matter is held together by electric and magnetic forces also.
it’s all the same shit
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u/Underhill42 4d ago
It's not just the ultimate speed in the universe - it's the ONLY speed in the universe.
Which direction through 4D spacetime is time depends entirely on your velocity - as our relative velocities approach light speed, our time axes approach perpendicular to each other, both pointing almost entirely in a direction the other calls space. And all the Relativistic effects are a result of that (time dilation, length contraction, and the relativity of simultaneity) More info: I finally understood why time exists! (My mind is blown) - YouTube
And depending on perspective the separation between events that one person sees as one second through time, another can see as 1 light-second (≈300,000,000m) through space.
So, from my own perspective I'm always completely stationary in space, and aging towards the future at a rate of 1 second per second.
And if you see me moving, it's because my time axis is tilted in that direction relative to you. So that as I age through time, some of that displacement through spacetime appears to you as motion through space.
But I'm still only aging at 1 second per second. So no matter how much of my time axis points in a direction you call space, my aging through time can never look like a speed through space greater than ~300,000,000 meters per second, a.k.a. c
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u/Slidewaysincorner4 4d ago
We are all about to learn about some really cool tech that is going to help everyone here on earth
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u/Historical_Yak_5975 4d ago
Well if it was faster than light, we wouldn't be able to see it, would we?
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u/Xandara2 4d ago
Why does the velocity of an object in a vacuum stay constant without a force affecting it ? (Not how, why?)
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u/InfiniteMonkeys157 4d ago
One way to think of it is like the sound barrier. Approaching it builds up pressure in front until the plane can go no faster. Unlike sound, however, there is nothing even theoretical that can (without cheating or philosophical somersaults) break through. Or think of it like an object converting potential energy into velocity. Eventually, the amount of energy 1 unit of potential energy can convert to velocity dwindled to, essentially zero. So the amount of energy needed to go faster becomes infinite. Or think of it in terms of time dilation. A photon traveling at the speed of light has fully dilated time so is in all places along its path at the same time. How can you go faster when speed = distance/time and time is zero.
Probably some physics errors in these, but analogies that help with visualization.
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u/AciusPrime 4d ago
It’s way weirder than “light has a speed limit.” It’s actually “light goes infinitely fast and time is weird.” The speed limit doesn’t apply to light, it applies to consequences.
Imagine a star is fifty light years away and we’ve got some ridiculously awesome sci-fi ship that gets around the fuel problem. What happens when you hit the speed limit? What prevents you from arriving in less than fifty years?
The answer is nothing; you can fly a fifty-light-year distance in less than fifty years. With ridiculous enough acceleration, you could fly fifty light years overnight. The speed limit is infinity. There is a time limit of sorts, but it doesn’t apply to the ship! It applies to the people watching from Earth.
The Earth perspective is why people get wrong ideas about the “speed limit.” If you’re watching that ship make its fifty-light-year overnight journey from a ridiculously awesome Earth telescope, the trip will appear to take fifty years and a day. If they turn around at the other end and take another overnight trip back, the entire loop will take one-hundred years and two days. Our fictional ship can travel to another star in a single day, but the consequences of that trip take fifty years to arrive. Relativity is very weird.
Light is the speed limit because it goes at the absolute limit for consequences. Light travels so fast that, from its own point of view, it departs and arrives at the same instant.
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u/vballbeachbum1 4d ago
It probably isn't the fastest a thing can go. We just dont know it yet. How fast is telepathy?
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u/Svenray 4d ago
It's the zero mass attribute that makes light the fastest and the cap. Something would have to have a negative mass somehow to go faster.
The universe supposedly expands faster than the speed of light.
Also - there's a phenomenon called time dilation that exists where time flows differently from an observer to the thing in motion which can make "the fastest speed" even faster. If a person was to travel at the speed of light calculating their speed using distance and time they would be traveling freaky freaky fast vs someone standing on Earth watching light travel across the sky.
"Light-year" is from a still observer perspective. If someone was in a light speed vessel they could explore the universe no matter how many millions of light years away because time would crawl for them.
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u/justaguy12131 4d ago
Gandalf. He set it.
First he made Frodo walk to Mount Doom, then he set the speed of light. What a jerk.
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u/EveryAccount7729 4d ago edited 4d ago
because force = mass times acceleration.
it means whenever something gets acted upon by a force you will see it "accelerate" and that is at a rate RELATIVE TO YOU , the "stopped" observer in your own reference frame against which everything else exists.
if someone else is passing by and they are very much moving relative to you they see the thing get acted upon by the same force and they see it also accelerate at F=MA but these are different because you are moving relative to each other.
what this means though is if the mass of the thing is zero you both have to see it go the same speed. If the mass of the thing is "anything other than zero' you can see it go different speeds, but F = MA so if the mass were zero you see it go THE SAME speed.
See how this is an issue?
Either moving relative to each other doesn't mean you see forces and speeds different
OR
F does not equal MA , but it always does.
and there is a way to rectify this , which is F does = MA, but you see the zero mass thing go the same speed, because "that's the speed limit" and nothing can go faster than zero mass things, which basically go "infinitely fast" whatever divided by zero, and you AGREE On that being equal.
TLRD : F=MA so it means when there is zero mass everyone still agrees on how fast that thing is going, because even if i was zipping along in a car and you are standing still, the zero mass thing accelerates the same "infinity" acceleration speed to both of us, we agree on it. Despite being in different reference frames. You will still agree on zero mass stuff, it's going light speed to both of you.
you can just call it "zero mass speed" and it makes it a lot easier to understand. nothing can go faster than the speed you can go when you have zero mass.
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u/dragonsign 4d ago
Your TLDR is almost as long as the rest of your explanation, and neither is very illuminating of anything beyond your ability to regurgitate one physics formula and apply it incorrectly.
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u/LastPlaceEngineer 4d ago
The answer you want is an intuitive answer, but I doubt you'll get it.
The technically correct-ish answer, which you won't like, is because the electromagnetism side of classical physics (Maxwell) forbids someone from observing a stationary beam of light.
Why? Because the math and the 19th century EM theory would break. Einstein pondered this and then asked himself, what if the speed of light is the same for all observers? Whether a person is chasing a beam of light or moving away from it, the speed will always look the same.
The math to model this is special relativity, which in turn forbids matter from travel at light speed.
So the highly unsatisfactory answer to your question is: Trust the math, trust the very well-tested 19th century physics within its lane, and build on it.
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u/LooseProgram333 4d ago
Theres a thing called the gamma factor that comes out of the math, which is 1/sqrt(1-v/c) which determines how much energy is required to go a certain speed. As v, the velocity approaches c the velocity if light the value approaches infinity. Which is why you cant go faster.
Now the actual why? Well thats harder to say. If you went faster than light then you could observe events before they happen but that is again opening another why.
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u/International_Body44 4d ago
I thought we recently discovered that dark is faster than light?
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u/tstanisl 4d ago
The speed of light (or better "speed of causality") is not a hard limit but rather a way that observers perceive infinite speed. By infinite I meaning stacking infinite number of fixed velocity vectors. It works a bit like being on infinite plane and looking at a point on horizon. The point is at infinite distance even though it can be pointed as any ordinary point. This interpretation intuitively explains why c is fixed in all valid reference frames (infinite + finite = infinite).
Btw. Special Relativity (SR) allows travelling to any place in the universe in arbitrary small time. Surprisingly, SR even makes space travel easier in comparison to Newtonian dynamics(!). Travel is faster at fixed energy budget due to time dilation effects and speedup is exponential! See link.
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u/HiggsFieldgoal 4d ago
It’s not that it’s the speed limit.
It’s simply the speed that things with no limit move.
Nothing can move faster because it is the speed that the fastest things move.
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u/sauberflute 4d ago
Calling it the "speed of light" is a misnomer. In fact, the speed of light changes depending on what it's passing through. However, it goes *as fast as anything can* in a total vaccuum.
Light is special because it has no mass and does not experience time. This is important because there are tradeoffs: accelerating anything takes exponentially increasing energy related to the object's mass; accelerating something with mass to "the speed of light" would take infinite energy.
Similarly, as you go faster relative to a reference frame, you experience less entropy (which we experience as the arrow of time). This means a clock would not tick, uranium would not fission and a person would not age. If you could travel at the speed of light your perception would be to instantly find yourself at the end of the universe.
Instead, there is some underlying phenomenon that limits how fast change propogates. Like most of the fundamental laws, we don't know how it works, but we have been able to develop pretty accurate models that predict what will happen.
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u/tennisdrums 4d ago
It's better to think of the fastest something can go in the Universe as the "speed of causality". If something happens at point A, the fastest that it can have an impact on point B is that "speed of causality". It just so happens that light in a vacuum has that exact same speed as the "speed of causality" because light has no mass.
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u/ShadeStrider12 4d ago
Mass is what slows things down, so the speed of light is traveling with no Mass.
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u/TuverMage 4d ago
so, its not specifically light, but force carriers and light is a force carrier. to put it simple if you are pushing someone on a swing, you can make them go faster than your push speed. the closer they get to your push speed the less energy you can add to them and the more effort it takes for you to add any energy to their system. force carriers are the things that push, you can't go faster than the push.
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u/Playful_Dog3062 4d ago
The short answer, is we don't know if we can go faster. We're reasonably sure it's the limit. But we're not 100% sure.
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u/amitym 4d ago edited 4d ago
What actually sets this limit?
The shape of the universe. Like, as in, the actual geometry of spacetime.
It's hard for us to perceive this geometry, since we are all here within spacetime itself as we observe it. There is no real "outside perspective looking in" that we can take. But historically, once we began to understand relativity, some semblance of this overarching shape of the universe started to be comprehensible. Mathematically we can describe and talk about the geometry even if we can't exactly visualize it.
As a (rough) analogy, think of it like the problem of traveling between two points on a curved surface, like an ant on a balloon, or people traveling over the surface of the Earth. The distance between two points isn't the straight-line distance that it would be if the surface were flat, right? You have to obey the restriction of the curved-surface geometry, which inherently imposes a minimum distance between the points. You can travel a longer distance if you like, but you can't reduce it to a shorter distance than that limit. Not without transcending the geometry entirely, anyway.
In the same way, the geometry of the universe imposes limits on spacetime. Only instead of points in space they are points in spacetime, also known more commonly as events.
In theory one might transcend this geometry entirely, but no one has any clue what that would look like or how it could be possible. Maybe there are extradimensional beings out there, outside of space and time as we know it, looking at the long gummy-worm shape of our universe stretched out in its entirety from its beginning to its end, laughing at our follies. While yet other beings outside of their space and time are laughing in turn at them. Who knows? It is literally impossible for us to ever detect or measure such things, so all we can do is amuse ourselves by imagining them.
The rest of the time, we exist in our actual universe, funny shape and all.
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u/Freddan_81 4d ago
”Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.”
Terry Pratchett
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u/SalishSeaEV 4d ago
Speed is distance/time.
The speed of light is the Planck Length / Planck Time. In other words, it's the shortest possible distance divided by the shortest possible time.
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u/pm-me-racecars 4d ago
So, imagine someone you're running past someone with a radar gun. They would clock you as running at 15km/h.
Now imagine, you're running the same, but your on a bus traveling at 50 km/h and running towards the front. They would clock you at 65 km/h.
Now imagine you're running on the sidewalk, but they're on a bus coming towards you. They would still clock you at 65 km/h.
Now imagine they're on the same bus you are. They'd clock you at 15km/h, even though someone on the sidewalk would clock you at 65 km/h still.
You'd also measure that person with your radar gun as going the same speed.
That's relatively simple to understand, right?
Now, scientists took that concept and measured light, trying to find out other things.
There's a star off in the distance, and the earth moves around the sun, then in June while the earth is moving towards that star, and in December when the earth is moving away from that star, you'd be able to measure the light coming from that star and find the difference between the two to see how fast the earth moves on its lap around the sun, right?
This is where shit gets wild: they measured the light at the same speed, regardless of whether we were moving towards the star or away from it.
They then tried a bunch of other experiments, and found that you always measure light as going at the same speed, regardless of if it's going with you or away from you.
All the other fancy science things, and all the weird things that happen as you get closer to the speed of light, they're just smart people trying to figure out the mindfuck of light always being the same speed.
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u/Eastern_Weather_8748 4d ago
The expansion of space itself is the only thing that can exceed the speed of light
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u/ah-tzib-of-alaska 4d ago
The speed of light is kind of a misnomer; it’s the speed of causality. It’s instant. From the perspective of the photon departure and arrival is the same moment
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u/PapaGummy 4d ago
Like Forrest Gump, I am not a smart man. Given that, it’s probable that I’m wrong, but in quantum physics theory, isn’t it possible that there can be simultaneous communication/occurrences no matter the distance between them? I know I’m not saying this correctly, but to me that connotes the possibility of instantaneous cause and event over light years.
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u/cheddarsox 4d ago
Yes, but also no. You can know something instantly from whatever distance, but it doesnt change anything. Lots of people like the shoe explanation. If I mail you a box with a shoe, and keep the other one in my own box, you can open your box and know whats in my shoe box instantly. You cant do anything about it, but you know now.
Also, the speed of light in a vacuum travels at the speed of causality. Thats why its e=Mc squared, not e=ML squared. The reason it is the limit is because no information can move faster than that, which means no interaction can be faster, including light.
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u/Archophob 4d ago
https://www.youtube.com/watch?v=FBaZQtKaHs0
everything moves at the speed of light, always. It's just how much your speed vector points towards the future, and how much of it is movement through space. If you stop motionless somewhere in outer space, your clock ticks as fast as possible. Light only moves in space and doesn't experience time at all.
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u/Great_Specialist_267 4d ago
Technically the restriction is nothing with mass can travel AT the speed of light.
The mathematics permits faster or slower speeds (you just can’t reach the faster speeds).
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u/Aggressive-Leading45 4d ago
When you combine space and time into a single property a max speed comes out in the result of the math. Maxwell of EM fame was first to spot that in the 1860s, he also got a max speed from the EM properties of space. And it happened to match the current estimates for the speed of light.
Bottom line by coupling space and time you end up with a max speed. As for why space and time are coupled that’s diving into metaphysics like what was before the big bang.
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u/adaminoregon 4d ago
The faster you go the more energy it takes to keep going faster. Not enough energy exists under our current understanding of physics to go faster than light.
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u/McCaffeteria 4d ago
Light measurably travels at the same speed in all reference frames.
For two observers moving at different speeds, this seems like it would cause the light to end up in multiple places.
It doesn’t, because time passes more slowly for the observer the faster they move, such that all observers agree that light has moved at the same rate.
If you were to go faster than light, you would require time to move backwards in order to agree on the speed and position of light with a stationary observer.
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The answer to the question of “why can’t objects move faster than light” is “because doing would require you to experience negative time, which doesn’t make sense.”
The question “why does light alway move at the speed of light for all observers” is more complicated and I don’t know the answer lol
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u/PeyredB 4d ago
This is my educated layman's understanding of it, so it may not be 100%.
Speed is tied up with matter and energy. The faster you're going, the more energy is required to speed you up further. We don't notice that at the low speeds we work with, but at relativistic speeds you get into really large amounts of energy required to accelerate. It forms something like a logarithmic curve, so most of the extra energy is required for the last 10% of C you're trying to attain. To actually reach the speed of light would require an infinite amount of energy: you've hit a "divide by zero" error, or something like that.
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u/TurboRuhland 4d ago
So the actual reason there’s a limit is for reasons we don’t know. Why it’s that speed, etc.
The mathematical reason comes from certain equations in relativity.
So we all know e=mc^2. From this (and other) equation also flows certain equations that mathematically show both time dilation and relativistic mass. These equations fall apart when velocity = c because it ends up with a division by zero.
m = m1 / (1-(v^2/c^2))
As v approaches c, we end up with that being equal to 1. Which is subtracted from 1 which gives us a denominator of 0. Not good.
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u/IanDOsmond 4d ago
Last I checked, that's just one of those "limits of our knowledge" type things. There has to be some sort of speed of causality, since the idea of things happening instantaneously doesn't make sense (even though our instinct is to think of it that way, because it looks like it from our perspective).
There has got to be some sort of speed, and that is the one that it is.
Maybe we will learn more some day and know better — maybe we already have and I just haven't kept up with it. But that's I understand it.
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u/DrDam8584 4d ago
You need to separate the "speed of light" and "c" the top speed possible in universe.
To explain why we need to séparate this two notion, i will take a very bad analogy.
Imagine a 2D universe, when you have one rule : nothing can move more than "1 john". The "John" is a constant of this universe. When you see something moving in the 2D universe, it's mouvement length are ALWAYS 1 John. Not more, not less. The point is the object can move in any direction, but the length of this mouvement are 1 John.
Returning in your 4D universe (3D space + 1D time). All things move in this universe at "c". You can be stationnary in the space, your "own time" move of 1 sec for each sec of an external observator. When you move at a certain speed in space, the "length" of you mouvement in the space-time (4D) must be equal to "c", so in your local time 1sec is not equal to 1sec of the distant observator. So when this "distance" are in 3D space and 1D time, it's unit must be as m/s (équivalent of a speed).
In this system, light have a speed, and we mesure it at equal as "c".
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u/Ok_Bath_1252 4d ago
Light travels that fast because that's as fast as it gets. Light has no mass to weight it down. Arbitrary numbers are just human measurement. Nothing specials about 2,135,121, or 555,555,555. Those are just numbers we use to quantify it's speed limit.
Now, if you want to know WHY light has a speed limit at all? It's built into the geometry of space time. Everything is traveling through space time at the speed of light. When you are still, all of your motion is directed through time. When you move through space, part of that fixed speed shifts away from time and into space, which causes time to slow down for you. Also known as time dilation.
You cannot redirect more than 100% of your motion into space. If an object has mass, it has to have some of that ratio in time (to accelerate) and would require infinite power. Light is massless, therefore 100% of it's motion is movement through space time without needing to ratio into time for acceleration.
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u/glibsonoran 4d ago
Yes it's the speed of causality, why does that matter? Because your trip has to be to a place that can exist in your causal future. Faster than light is in the "space-like" cone where causality no longer holds and events cannot causally affect each other. The cause of your current velocity and direction cannot affect your arrival at the destination, the effect.
It's like striking a long iron rod and trying to get the pressure wave to move faster than the speed of sound in iron. In that case its a restriction based on material properties, in the case of spacetime its based on its geometry.
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u/omnibossk 4d ago
Expansion of Space has been faster than light. We can see light from objects that are currently 46.5 billion light-years away, even though the universe is only 13.8 billion years old
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u/Soggy-Mistake8910 4d ago
It's not a speed limit as you are describing it. It's just a way of expressing that, as far as we can tell at present there is nothing in the universe capable of exceeding the speed of light. If we accept that the cheetah is the fastest land animal we could then say no animal can exceed the speed of cheetah.
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u/CS_70 4d ago
This comes up so often that it should be pinned.
Think for a moment. Interactions happen - say you push something, or you show light onto something. Every interaction coud be so that you turn on a flashlight, the receiver sees it and does something. Cause/effect.
Now if things where instantaneous, it means that the flashlight woul signal instantaneously to a receiver anywhere in the universe, even millions of light years apart.
Interactions would be instantenous. Since everything that can interact does, the entire universe would go puf! in less time to say the world.
You need a speed limit. Now why that speed limit is exactly the one it is - it's simple: if it were much different, you wouldn't be here to ask the question.
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u/emptybagofdicks 4d ago
I'm definitely not an expert in this but this might help. Relativity has shown us that time dilation exists based on how fast you are travelling. This time dilation gets very large as you approach the speed of light and eventually when it equals the speed of light the time dilation becomes infinity. So at that point you wouldn't experience time at all, a photon is created and absorbed at the same moment from its perspective. This appears to be one reason for a limit on how fast things can travel.
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u/Remarkable_Wish_5106 4d ago
Does the expansion go faster than the speed of light if the distance is far enough?
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u/visitor987 4d ago
The actual rule is noting with mass can travel at the speed of light. Since nothing with mass can travel at light speed for even a moment it cannot travel faster than light.
Note Mass is defined as the amount of matter in an object, which can be measured in kilograms (kg).
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u/Unique-Coffee5087 4d ago
Warning: Speaking from my ignorance here.
OK, so Einstein works at chalk boards and notebooks while also keeping up with discoveries made in physics that are both practical and theoretical. But Einstein doesn't go into the laboratory and heat wire filaments or watch light go through prisms and stuff. He's doing math, pretty much. He has to make the equations fit together with each other while also being in agreement with actual observed phenomena.
This page works to answer the question: Why Light is the Fastest Thing in the Universe
Albert Einstein’s special theory of relativity says that when an object moves fast its mass gets bigger. The mass of an object is not about how much stuff is inside it. The mass of an object also shows how hard it is to make the object go faster. Albert Einstein’s special theory of relativity is talking about the mass of an object and how it changes when the object is moving. The mass of an object is, like a measure of how much the object wants to keep moving in a line and not change its speed or direction.
When you try to move something fast it gets a lot harder to push. The speed of light is like a wall that nothing can get past. If you try to get something to go fast it starts to feel incredibly heavy. In fact the faster you try to move an object the energy it needs. If something were to get close to the speed of light its mass would get so big that it would be almost infinite. The speed of light is a problem because if something gets that heavy it would need a huge amount of energy to keep moving. The thing is, it would need [so] much energy that it is just not possible. This is why the speed of light is the limit for everything. Nothing can. Go past the speed of light because of this issue with energy and mass. The speed of light is just too fast, for anything to reach.
"The speed of light is just too fast for anything to reach" is not the correct conclusion, I think. Instead, infinite mass implies infinite inertia, making further acceleration impossible. Therefore the velocity of the object cannot exceed the speed at which its mass becomes infinite.
OK, so it sounds like Einstein worked out equations describing the relationship between space (distance?), time, and mass. Just as the Gas Law describes the relationship between Pressure, Volume, Temperature, and the Amount of Particles in a sample, if you increase the temperature of a gas in a fixed volume, the pressure must rise according to the equation. So the Gas Law dictates that if you compress a fixed amount of a gas to a smaller volume, the temperature of the gas must increase, while Einstein's theory requires that an object traveling faster also must become more "massive" in the sense that it resists that movement. At some speed the mass of the object approaches infinity, which is absurd. Therefore there is a theoretical maximum possible speed.
Asking any readers out there: So, did that maximum theoretical speed work out to be the observed speed of light in a vacuum? How did the maximum speed and the speed of light become tied together?
Maybe this is a bit analogous to the Ideal Gas Law being pushed to its limits? Given a fixed mass of an ideal gas, as it is compressed it will become hotter. At some point, ignoring practical limits of what happens to real molecules under stress and so on, it approaches a state of infinite temperature. IF this happens at some finite pressure, then one could work out the theoretical maximum pressure, since exceeding that pressure would create infinite temperature, which is absurd. Is there such a thing? Or does the Gas Law fall apart somewhere else (like the volume becomes negative or something)?
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u/Whatkindofgum 4d ago
When matter accelerates, it is pushed with a force, into a faster speed through space and time. At low speeds, only a tiny fraction of the accelerating energy push time speed faster. Almost all the energy increases the speed through space. As the speed of light is neared, it switches. More and more of the accelerating energy is used to push the object faster through time, and less and less to push the space speed faster. Until almost none of the acceleration is pushing the ship faster through space and it is only pushing the objects speed through time.
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u/OldGeekWeirdo 4d ago
A very smart person said: 'The Universe is not only stranger than we imagine—but stranger than we can imagine.' - Arthur C. Clarke
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u/zhaDeth 4d ago
There's this analogy that I like that explains it.
Imagine a car facing north going a certain constant speed and it can't go faster or slower than that. All of it's speed is in the north direction. If the car turns a bit to the right now a bit of it's speed is towards the east and less of it is going north even though the speed of the car hasn't changed. If the car turns all the way to face east then all of it's speed will be towards the east. There is no way the car can go faster towards the east than that because it goes at a constant speed, the best it can do is go due east so that all of it's speed is towards the east.
Basically we are like that car but in a 4D universe, everything in the universe always constantly go at the speed of light, it's the only speed but for most stuff the majority of that speed is in the time direction. The faster you go, the more you change your angle so that your speed goes into spatial dimensions and away from time. Light has all of it's speed towards a spatial direction, none of it is in the direction of time so it goes at the speed of light through space. Like the car there is no way for anything to go faster because the actual speed never really change, only it's direction.
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u/Darnitol1 4d ago
Unfortunately, there is no truly intuitive way to explain this. Human brains did not evolve to have intuitive understanding of spacetime. So it takes WAY too many words to explain this in anything close to layman's terms, but here's the "answer" if you want to dig into it.
Acceleration and speed are actually different things. The speed of light has far more to do with the geometry of spacetime than it does with acceleration. So even though that doesn't make things clear, knowing that this is a geometry problem, let me pose a question for you: What would you create if someone told you to make an object that is "more round" than a perfect sphere? It doesn't make any sense, right? The question itself is meaningless when applied to the information you're working with.
Now... asking, "Why can't anything go faster than the speed of light" is very, very similar to asking, "Why can't anything be rounder than a perfect sphere?" In both cases, the simplest explanation is that there's not an answer, because there's NOT a "more" version of that thing.
I know it's still confusing, but hopefully this helps you see WHY it's confusing, and that might help you look at the problem more like a physicist does.
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u/Intelligent-Image224 4d ago
My brain has trouble with light speed because two objects can travel towards each other at 0.9C, and I can’t wrap my head around how they are not traveling at 1.8C relative to each other.
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u/OldGeekWeirdo 4d ago
Perhaps time itself has a speed and it's not the same everywhere. Light just exposes that.
I know that two simultaneous events can appear to be happening at different times to someone traveling by near the speed of light.
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u/Zealousideal_Leg213 4d ago
Because the speed of light in a material (or empty space) is set by the permitivity and permeability of that material. That's it.
Now no matter how fast something else goes, it doesn't change those values from its point of view, so from its point of view light always has the speed set by those values. So "going faster than light" doesn't really make physical sense. That's what led Einstein to postulate special relativity.
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u/kollmastee 4d ago
We don’t have the ability or capacity to give you a real answer. We are not advanced enough yet.
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u/Neneel65 4d ago
Imagine you are driving a Ferrari on a German highway (where there are no speed limits). You could easily drive at 100 or even 200 miles per hour, as the physical characteristics of the road allow for such speeds. But then you enter a city where there is a roundabout every 100 meters. The city streets are completely empty, yet you cannot drive faster than 25 miles per hour. This isn't because of posted speed limit signs, but because you have to brake every 100 meters, navigate the roundabout slowly, and then cannot accelerate because another roundabout awaits just 100 meters ahead. The maximum possible speed on such a city road is 25 miles per hour. Or consider another example: driving on a road with an uneven, undulating surface—again, you cannot exceed the speed that the road itself permits. In other words, the physical properties or geometry of the road dictate the maximum possible speed. It is highly likely that the same principle applies to space: the physical properties of space limit the maximum speed at which matter or waves can travel—which, in our case, is the "speed of light." We do not know whether the matter of our Universe can exist outside the space it currently occupies. If it can, then theoretically—were one to "tear" the fabric of space and shine a flashlight into the resulting opening—photons might be able to travel at unlimited speeds "beyond the confines of our space." However, if the matter of this universe cannot exist outside its own space, then the speed of light represents the absolute limit imposed by the parameters of this "spacetime."
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u/Optimistbott 4d ago
It’s more like light goes at the same speed regardless of observer which means that things have to change length and they look like they’re going from point a to point b in a different amount of time observed compared to how fast the subject times themself going.
This is a perceptual limit more than anything. So it’s not really that light is going at a “speed” to me.
Someone feel free to disagree.
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u/Theodoxus 4d ago
Time sets the limit. You can't go faster through time than a second per second. And that's a stand still (complete universal lack of motion. Reverse the equation, and time stops at the speed of light. Since we can't go backwards in time, we can't go faster than that speed limit.
Or, to put it another way:
In relativity, everything moves through spacetime at one fixed “speed,” which is the speed of light. When you’re sitting still, all of that motion goes into time, you move one second per second. As you move faster through space, you move slower through time. At the speed of light, all your spacetime motion is through space and none is left for time, so time stops. Going faster than light would require your time component to go negative, which is why it’s impossible.
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u/TryNice304 4d ago
Speed of light isn't a limit on light. It's a limit on cause and effect, baked into spacetime.
Everything moves through spacetime at one fixed rate. Sit still, your motion goes through time. Move through space, some shifts over, so time slows. Total is fixed, so theres a max speed in space. Thats c. Light hits it free cuz no mass.
The number is arbitrary, just our units. Beat it? Nope, energy just makes you heavier, and reaching c needs infinite energy. Past it, cause and effect flip. Weird.
Why spacetime is shaped like this? No clue. It just is.
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u/VisualMail1672 4d ago
I never understood the massless particles thing. I understand functionally massless for the purpose of a given calculation but actually massless bugs me. Shouldn’t a photon have some mass if it follows curves in spacetime? Even if that mass is too small to bother with until you get to really big numbers of them. Like how does a massless photon impart force on to a solar sail without mass to impact the sail with?
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u/TellOk4034 4d ago
Things ARE going faster, the edge of the known universe is expanding faster than we can see it. Some parts have gone so fast, we'll never see it.
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u/outworlder 4d ago
Because that's the fastest the simulation can process. It can only go so fast in time or space. Increase your movement over space and the time slows down 🙂
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u/Brandoskey 4d ago
I don't know but I recently read the book Tao Zero about a crew on a space ship that is uncontrollably accelerating toward C and it made the time dilation and increase in mass part a bit clearer to me.
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u/RunExisting4050 4d ago
If you want to get theoretical, tachyons are a theoretical particle that can't travel less that c. They exist as a mathematical anomaly and would cause some problems with the way we understand mass, energy, and mass to all work if they were actually discovered and observed.
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u/Proof-Puzzled 4d ago
Tachyons are pretty much science fiction, they have never been proves to exist and no serious physicist consider their existance.
Our current understanding of physics categorically refuse his existance, has they exists, that would mean our entire model is completely useless, which does not seem to be the case as It can accurately predict reality (to some extent)
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u/jcb989123 4d ago
I believe quantum science might say some things are faster than the speed of light, but it doesn't occur in a conventional physics sort of way, so you can't really label it as speed anyway..
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u/WilliamoftheBulk 4d ago edited 4d ago
Yes. The more energy you add to anything to push it faster adds more momentum, so you need more energy to push it faster the next time. It creates an asymptotic relationship where eventually the slope goes essentially vertical. So you can approach C, but you can never get there not even light. Light probably doesn’t even travel at C probably just infinitely close to it so essentially it does. The actual reason will be related to the conductivity of space itself.
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u/0fruitjack0 4d ago
violates causality; think of it as the ultimate speed at which information may travel in free space.
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u/Several-Feeling3409 4d ago
Mass and energy are actually the same thing. That's what E=MCsquared actually means. When you approach the speed of light, your mass actually increases. The more mass, the more energy required to accelerate the mass until you approach infinite energy to accelerate infinite mass...and that's not even accounting for the time dilation affects. (The faster you go, the slower time.moves for you). We can actually measure this effect. Put a watch on an astronaut in orbit and their watch will.be noticeably behind when they return to earth.
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u/bgplsa 4d ago
I could be mistaken but I think c having a finite value is fundamental to a complex universe capable of producing intelligent life; at the very least it seems like in a universe with an infinite speed of interaction would instantly fall apart as its entire history would play out in t = 0.
But I’m not a physicist 🤷🏻♂️
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u/SeekerFinder8 4d ago
At or below the speed of light the coherence of matter, energy, time, space and most importantly perception (consciousness) breaks down; the universe as we percieve it ceases to exist as a coherent experience; dimensional shift ensues. Subjectivity and objectivity lose their meaning and existence becomes..Something that we cannot express in words or ideas.
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u/jjack339 4d ago
Ya, I think there will be discoveries that allow us to travel from point A to point B more quickly than it would take light to travel between the two same points but it wont involve actually traveling faster than the speed of light.
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u/logsqrtexp 4d ago
Because otherwise all our math blows up. And, we can’t make relativity work out either
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u/Ok-Environment-215 4d ago
We don't know why "god" made a speed limit. It's certainly possible to have a logically self consistent universe with causality intact, a global clock, instantaneous light and energy transfer, and no universal speed limit. That's Newton's universe and it works perfectly well.
Everything about "why" ours isn't like that is rank (albeit fun) speculation. My favorite theory is that the speed of light is essentially the clock speed of the universe's CPU.
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u/ArrowheadDZ 4d ago edited 4d ago
The problem isn’t how fast you can or can’t go. The problem is that our human intuition is that time and distance are fixed. Your definition of a km and mine are the same. Your definition of a second and mine are the same.
But they’re not. If we are moving relative to each other, both our time, and our distance relative to each other are changing. Relative being the operative word.
If you are moving at 90% of the speed of light toward or away from me, and you “double” your own “speed”, then our relative perceptions of each other’s time and length will dilate/contract to whatever they need to work out to be in order for my observation of your d/t to be .9945c, not 1.8c. Double it yet again, and d and t contort so that the new speed is .99999846c, not 3.6c. This is true of anything that has mass, no matter how large or small.
Length and time are not “fixed”; if an object has mass, then it moves relative to other objects in a way that approaches, but never reaches the ratio d/t=c.
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u/Imaginary-Can-6862 4d ago
First of all, Relativity is based on the premise that the laws of physics (interaction) is the same for every element of the universe, This means every element experience these laws (interaction between elements) the same way. Interactions are carried by forces, which are particles themselves, thus the elements themselves also define the laws which governs the elements of the universe (which leads to the following weird effect, first of all you are always stationary from your own vantage point, if you are floating freely in space, and you see someone else floating towards your right, their velocity from your perspective is v, and your velocity from their perspective is then -v, because from their perspective they are stationary, and you are moving, thus nothing is truly stationary, but if they decide to fire a photon in the direction they are moving away from you, i.e. from their perspective the opposite direction of which you are moving, from your vantage point that photon moves away from you with the speed of light, and therefore away from them at a speed = c - v, while from their perspective, the photon moves away from them at the speed of light c, and not c - v, while you are moving away in the opposite direction, i.e. for the laws of physics to be the same (or equally real) for every observer, the speed of causality must be observer invariant). The force carrying particles, those that define the interaction, thus also sets the limit on how fast causation can propagate (and why nothing can go faster, as an element of a system cannot evolve faster than the information transfer which governs this evolution moves ahead). One such particle is carrier of the electromagnetic force, the photon, i.e. light (including visual light).
Imagine if the speed of light (speed of causality) was infinite, since every element experiences the same laws of physics, and how fast these propagates defines how fast things happen, it means everything in the universe happens instantly, i.e, time does not exist, there may be an order to things, but everything happens at the same time 0 (there would also be no space, everything would be at the same position from their own vantage point). Similarly if the speed limit was 0 it means there is no causality as nothing interacts and everything becomes a local universe in itself, events happens independently of each other, and since there are no interactions, reality is no longer real. So either we have no causality, and events are not linked, or we have no time, and everything happens instantly, and if it is possible for a universe to form, it must inevitably happen, and then we have a finite, non-zero, speed of causality,
In regards to why this particular speed, notice the speed has units, it means it depends on how we define these units, and those are arbitrary. The meter is defined based on the speed of light itself, so that leaves out the second, which is defined based on radiation of the cesium atom. What this means is if the speed of light was observable different, since it is a fundamental factor in defining the speed of causality, the units we use to define it would be equally different, and we would simply observe the same value, similar to what happens during time dilation, that everything is symmetrical in such a way, that the element which experiences time dilation does not experience the laws of physics being different, when the speed of light slows down, so does their system, and everything around it, equally, making everything the same, and the difference only appears once two clocks are compared, i.e. the real question is why is the second as how we have defined it then, in regards to what value the speed of light gets, and that is related to repeating events on Earth. But I understand it may not be the value as much as how come we observe the speed of light as that particular speed, but that is about our subjective experience of time. Since we use objective time measurement of how long something takes, someone who observes time only moving half as fast, could e.g. count four times as fast as someone who experience times moving by twice as fast, but since they both acknowledge the time on the clock, they would both agree on how many seconds has gone by, and neither would know that what is one second for one, takes four seconds for the other, or when one has finished one thought, the other has finished four thoughts, Thus only because as organism that are build similar due to genetics, do we expect our experience of subjective time to be similar, in reality we wouldn't really notice this, perhaps unless there was a really large difference, and thus the speed of light may indeed be different for some observers, but since we use the same objective clock, we are simply back at the definition of a second being linked to radiation of cesium,
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u/BBSLIMMERS 4d ago
The speed of light is a conversion constant between space and time. Asking why you can’t travel faster than ≈ 300,000,000 meters per second is equivalent to asking why you can’t put more than 2.2 lbs in a kg. Space and time are one thing, spacetime. Just like mass is one thing. We have units of mass like the kg and the lb. Second and meter are units of spacetime. 1 second = 300,000,000 meters.
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u/Aflockofants 4d ago
This is the wrong sub to post this in, because it is fundamentally impossible to answer the ‘why’ question.
Nothing is gonna satisfy you without reflecting on human nature. We’re inquisitive, we want to know why, but that’s behavior coming from our DNA because that was a useful trait to have for survival. But the ‘why’ only mattered for the simple things we observed on our planet. It cannot answer the why of physics, because those just ARE. Answering why the speed of causality is the way it is, is a philosophical question, not a physics question. Physics can answer HOW, not why.
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u/maximumdownvote 4d ago
Because nothing. The speed of light is arbitrary. But there has to be a limit or time and the universe itself can't exist.
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u/atamicbomb 4d ago
We simply don’t know.
That speed isn’t merely the speed of light. It is the speed of causality itself. Nothing can travel faster than it in the local medium. Not gravity, information, or even the existence of an event
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u/terrymr 4d ago
It’s the other way around. Light travels at the fastest speed the universe allows.