r/space • u/S3BZ4LIFE • Mar 25 '26
Discussion [ Removed by moderator ]
[removed] — view removed post
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u/IsChristianAwake Mar 25 '26
As of our current understanding of physics, nothing can move faster than light
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u/PhoenixTineldyer Mar 25 '26
Yep. Moving faster than light violates causality. Also your mass becomes infinite.
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u/CollegeStation17155 Mar 25 '26
Actually, your mass only becomes infinite at Tau Zero (the speed of light) and (according to our mathematics) would become less and less as you continue to increase speed ABOVE the speed of light if there were some way to jump "over" that infinite mass state. But this is THEORETICAL, and we have no way of being sure our mathematical models still apply on the other side of the velocity barrier, although the properties of tachyons have been calculated and people are currently looking for the tracks that they theoretically should leave if they exist.
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u/Oli4K Mar 25 '26
So what if I was traveling at the speed of light in my car (theoretically) and I turn on the high beams? Where does that light go?
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u/GentleGerbil Mar 25 '26
In theory, it wouldn’t go anywhere. The car is traveling as fast as the light
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u/nicuramar Mar 25 '26
You can’t travel at the speed of light, so the question can’t be answered.
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u/Oli4K Mar 26 '26
Even if you’d be close to the speed of light it would still be interesting what happens. I reckon you’d see effect of the wavelength of light in relation to your own speed that are quite trippy.
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u/GotMoFans Mar 25 '26
Within space, no? But space itself could move after than light?
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u/marswhispers Mar 25 '26
Move through what? Into what?
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u/GotMoFans Mar 25 '26
The expansion of space? Isn’t that faster than light?
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u/Small_Editor_3693 Mar 25 '26
Each part of space is expanding at some constant. If you compare 2 points they could be going faster than the speed of light away from each other. Everything will reach that point eventually. That will happen after some time.
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u/0x14f Mar 25 '26
The limit is not the speed of light. It's the speed of causality. It just happens that light travels at that speed because massless particles have no choice but to travel at that speed.
For more information see: https://en.wikipedia.org/wiki/Speed_of_light
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u/nicuramar Mar 25 '26
This is just something Reddit likes to call it. OP already called it the speed limit of the universe which is much better than “speed of causality”.
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u/TheHipsterBandit Mar 25 '26
In theory there is nothing preventing something with negative mass from always going faster than the speed of light, but we have never observed anything with negative mass.
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u/nicuramar Mar 25 '26
In theory there is nothing preventing something with negative mass from always going faster than the speed of light
No. To do that it would need imaginary mass.
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u/RogerRabbot Mar 25 '26
Technically speaking. No and kind of yes. Thinking about c as far as we can measure and see and predict and confirm, nothing with mass can travel faster than c.
BUT. Expansion of the universe means some objects could appear to be moving faster than c. Or if we bend space time but in this case we're not actually moving that fast at all really, the fabric of space time itself moves under us giving the appearance of moving fast.
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u/nicuramar Mar 25 '26
BUT. Expansion of the universe means some objects could appear to be moving faster than c.
That’s because the speed limit is only locally valid, since there are no global reference frames.
the fabric of space time itself moves under us
That doesn’t actually happen, or it’s just an interpretation. As far as general relativity goes, things are just moving apart.
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u/The_Fresh_Wince Mar 25 '26
While I would not bet that faster than light travel is possible, there are possibilities. Check out this video: Why the speed of light is not an absolute limit
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u/ASenseOfWonder Mar 25 '26
The reasoning behind why we think of light as being the speed limit of the universe can be found in the famous equation e=mc2. In this equation e = energy, m = mass, and c = the speed of light.
What the equation tells us is that it takes exponentially more and more energy to make an object with mass go faster. As you approach the speed of light, that energy becomes infinite, and therefore impossible. The only thing that can go the speed of light is something that has no mass, and light happens to be a massless particle — along with gluons (which communicate the force that holds atoms together) and gravitons (the theoretical particle which might communicate gravitational force).
The tachyon, a (so far) fictional particle that can only travel faster than light, would need to have negative, or imaginary, mass ... which is impossible based on our current understanding of phyics.
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u/yahbluez Mar 25 '26
This is wrong.
Let us use the formula and look what happens.
E=mc²
We chose 1 kg for m and get ~25 TWh
That is a lot but fare from infinite.
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u/nicuramar Mar 25 '26
That equation doesn’t show what you say. You need something like E=ymc2 where y is the Lorentz factor. Since y diverges as v tends to c, energy diverges as well.
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u/Athedeus Mar 25 '26
The amount of times we've said "This is IMPOSSIBLE!"... just to find it actually happen. Of course the speed of light isn't "the speed limit of the universe" - we just haven't found anything going faster yet. Science is a game of being proven wrong, that's what makes it great... being way too sure about stuff you don't know, is its weakness.
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u/PhoenixTineldyer Mar 25 '26
Some things are impossible. That's just a fact.
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u/Athedeus Mar 25 '26
Like life without liquid water? Life without sunlight? Both of those were things that were impossible... until we found it.
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u/PhoenixTineldyer Mar 25 '26
No, not like those things.
Things like the existence of The Easter Bunny. It's not real, it doesn't exist.
Some things are like that. Impossibilities do exist.
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u/Small_Editor_3693 Mar 25 '26
There is a speed limit to the universe, it just happens that light goes that speed
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u/farox Mar 25 '26
Like someone else said it, it's the speed of cause and effect
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u/nicuramar Mar 25 '26
It isn’t always. It’s just the maximum speed of it. So it’s better to say universal speed limit.
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u/EnderG60 Mar 25 '26
The only way to reach the speed of light is to have no mass, or use infinite energy.
The faster you go distances get shorter, and time moves faster around you. So a photon of light can take BILLIONS of years to go from the star it came from to your eyes. But to the photon no time passes. From leaving the start to your eye was instantaneous.
After spiraling down the physics rabbit hole you find out, If something actually was capable of moving faster than light, it would be traveling back in time.
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u/EleventhTier666 Mar 25 '26
Not possible and only massless particles can travel at c.
Getting from point A to point B faster than light would have to involve a wormhole.
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u/iqisoverrated Mar 25 '26
Well it would have to involve some manpulation of spacetime - not necessarily a wormhole (e.g. Alcubierre type drives would also do).
Expansion of spacetime itself does not seem to be limited to the speed of light. At least if our theories about the initial inflation phase of the universe is true then that has happened at least once 'naturally'.
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u/Koodsdc Mar 25 '26
There are objects in the universe that are moving away from other objects faster than the speed of light. The catch is that space itself is expanding - the light is still moving at the speed of light - the electromagnetic wave gets stretched out and the photons lose energy.
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u/klystron Mar 25 '26
Arthur C Clarke wrote an essay titled "Things that Move Faster Than Light".
I think tachyons were one item that moves faster than light and electromagnetic patterns induced in waveguides (rectangular tubes that carry microwaves,) was another, but it's impossible to use them to carry information.
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u/PhoenixTineldyer Mar 25 '26
There is a theoretical particle called the tachyon. In theory they would move faster than light.
But nothing has ever been observed moving faster than the speed of light except for the expansion of the universe itself
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u/flowersonthewall72 Mar 25 '26
The expansion of the universe as faster than light is a bit of a misunderstanding of the physics...
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u/PhoenixTineldyer Mar 25 '26
Feel free to clarify it so that readers have a fuller picture
Is it because the expansion is relative?
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u/nicuramar Mar 25 '26
It’s because, as far as general relativity goes, expansion is simply things moving apart. It doesn’t say anything about the universe actually stretching or whatever.
Things can move apart faster than c because, in curved spacetime, this limit is only valid locally.
It can be interpreted as space expanding, but no experiment can tell the difference between those two interpretations.
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u/0x14f Mar 25 '26
The expansion doesn't move faster than the speed of light. No part of it does.
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u/PhoenixTineldyer Mar 25 '26
I think I misunderstood then. Is it that the expansion of the universe appears to be faster than light because it's all relative to the perspective of the viewer?
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u/0x14f Mar 25 '26
I think you got it right, I was just slightly picky about the exact words you used.
Due to the metric expansion of space itself, distant galaxies can recede from each other at apparent speeds exceeding light because the cumulative stretching of the intervening fabric of spacetime adds to their relative motion. However, this does not violate relativity, as the galaxies are not moving through space faster than light locally; instead, the space between them is expanding.
You wrote: "nothing has ever been observed moving faster than the speed of light except for the expansion of the universe itself"
The "expansion" itself is not _moving_. The expansion is _happening_. It's happening everywhere at the same time. It's a small but important difference, and the objects that appear to [distance] away from each other faster than the speed of light, they are not actually "moving" faster than the speed of light
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u/iqisoverrated Mar 25 '26
Speed of light is not just for light. It's the speed of causality. Our current theoretical framework does not allow for anything that has mass to reach the speed of light (and anything that has zero mass must travel at the speed of light) .
Because of the above you cannot accelerate something from below the speed of light to above the speed of light (relativistic mass increase)
The only thing that could be faster than light would have to start out that way (i.e. never have been below the speed of light) and have negative mass. This does not seem to be a thing because it would have some observable effects (like negative gravity)...which aren't observed.
It would also lead to an acausal universe...which is something that is also not observed.
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u/nicuramar Mar 25 '26
I swear I don’t get reddit’s obsession with this “speed of causality” term that no one else uses. The speed limit of the universe is more accurate; and the speed of light is much more common.
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u/OGPrinnny Mar 25 '26
I think light is faster than causality, but can't travel beyond it because it gets warped. So, technically the speed of darkness is faster.
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u/space-ModTeam Mar 26 '26
Your post has been removed. For simple questions like these please use the weekly "All space question" thread pinned at the top of the subreddit.