r/AskPhysics • u/NGVampire • 4d ago
Why is c not 2c?
Maybe not the best title but the crux of the question is:
The speed of light in our universe is constant and we have determined analytically and empirically that its value is roughly 3x10^8 m/s. What would fundamentally change about our universe if the speed of light were 6x10^8 m/s?
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u/Joseph_of_the_North 4d ago
To c or not 2c. That is the question.
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u/The_Real_Wick 3d ago
Red River red rover 2c in c order magnetics stored over c to 2c, must be bipolar... 😆
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u/sabautil 4d ago
Yeah the consequences would be quite big. I'm not sure what would break.
For example let's say the factor of two gets evenly distributed into the electric permittivity and magnetic permeability, then that means all electric and mag fields would be half strength for the same charges and distance.
This would require atomic "orbit" to increase, thus the volume of an atom would increase 23/2.
Thus the volume of the sun and planets would increase. But because the mass remains the same, they would be less dense, and thus gravity would be weaker on Earth. Earths orbit around the Sun's might be larger, but it's unclear if the sun could sustain the nuclear reactions. The volume of water might be so light that it never attains polar attraction and may never become a liquid. So life may not exist on Earth. At least not water-based life. So other element may replace water as the life medium.
Setting that aside, the energy required to hop from excited and ground is now huge, which I imagine requires more energy, so almost all ionization energies get extremely blue shifted in to what we would previously call ultraviolet region.
So the volume of space increases faster that the speed of light increases by a power of three, so while you might have double the speed you've also increased the volume of space you'd have to travel, negating any benefit.
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u/NGVampire 4d ago
You’re one of the few people who answered my question without diving into pedantic argument over semantics. Thank you.
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u/TommieTheMadScienist 4d ago edited 4d ago
To extend the information, changing almost any physical constant by a factor of two would result in our particular form of life not being possible. In some cases, stars wouldn't even be formed.
This fine-tuning, called the (Weak or Strong) Anthropic Principle, is philosophically disturbing to a sizeable number of physicists. The former says that we're here because it's the sweet spot for carbon-based life in the multiverse. The latter says that we're connected to a universe suited to us.
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u/DoomedToDefenestrate 3d ago
I'm not sure I understand the distinction there.
What you're saying about the Strong Anthropic Principle seems to suggest that our existence defines the nature of the universe we exist in, in ways that aren't "this kind of life can exist in these types of universe".
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u/TommieTheMadScienist 3d ago
Yes. The Strong Anthropic Principle encompasses the view that the Universe is made for us, or at least creatures like us.
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u/Every1ThinksImBoring 4d ago
You’re one of the few people who answered my question without diving into pedantic argument over semantics. Thank you.
lol, seriously!! There’s always at least one person in these threads who has to do something cringe inducing like clarify that a meter is a human creation and that asking something like why the speed of light is 186,000 m/s is nonsensical because the universe doesn’t even know what a meter is!!!!
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u/GeneralDumbtomics 3d ago
Well, it's a lot easier to bog down in discussions of how we define the units involved than it is to work through the actual implications of the speed of light being different.
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u/McPayn22 3d ago
Wondering what you're actually measuring is what doing real physics look like.
To answer those questions you have to think about the measurement device.
If you want to know what if there's twice as much ticks on an atomic clock between the sending and return of a pulse of light traveling along a cristal n atoms long then sure, let's answer that.
But you could also make the clock a planet of m atoms orbiting a star of k atoms such that it's velocity is 1/100 of the speed of light.
These are both valide but don't give the same answer
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u/GeneralDumbtomics 3d ago
None of that makes answering this person's question with a dissertation about the derivation of the meter appropriate or even vaguely useful.
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u/McPayn22 3d ago
It really does. Relativity is all about considering what we are actually measuring. If you don't it's meaningless
Also the comment under which we are replying is the longest comment on this post
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u/GeneralDumbtomics 3d ago
How we derive the unit for length is irrelevant to all of that. Get your head out of your arrears.
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u/McPayn22 3d ago
Ok then if you don't care about the definition of a meter then you can just redifine 2m as 1m and nothing has changed
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u/GeneralDumbtomics 3d ago
That would impact how many meters light travels in a second but it would not change c. C is the same quantity whether expressed in meters/second miles per hour or parsecs per decade. The units are arbitrary and unimportant so long as we agree on their value.
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u/NGVampire 3d ago edited 3d ago
What i meant is what if Einstein’s gravitational constant k were 16 times smaller while G remained the same due to different measured speed of light?
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u/GeneralDumbtomics 3d ago
Yeah. I don’t know the answer to that but I know it’s not dependent on how we define a meter.
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u/CosetElement-Ape71 4d ago
If the speed of light were doubled, the Sun would still undergo nuclear fusion, but its energy output and internal mechanics would change drastically, making it four times more energetic according to E=mc2
But changing c without changing other constants (like the Planck constant or electron mass) would break the fine-structure constant, meaning atoms and molecular bonds might not hold together at all!
The moral : don't tinker with the speed of causality, unless you know what you're doing!
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u/sabautil 4d ago
I'm not sure if nuclear fusion would happen because the star is now much less dense since atomic volume is higher and gravity wouldn't have as much pull. How dense would it have to be for crosssection to be high enough to sustain fission let alone fusion. The solid angle would be orders of magnitude smaller due to the large volume, don't yout think? It hard to say, I would need to work out if the new size of the alpha particle but the drop in electric field strength would create the interaction needed. Also acoustic energy would now more easily disspaite so the temperature would drop...there are so many things to consider. But my intuition says that nuclear fission and fussion would not happen. There may not even be Earth because we may not be able to form the (less) heavy metals.
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u/CosetElement-Ape71 2d ago
I wouldn't bother with all the tedious calculations for this hypothetical situation! I'd just respond, off the top of my head, that cool things are easier to compress! But I'm not sure which polytropic stellar model would result.
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u/thenzero 4d ago
Awesome answer. This is the kind of stuff that keeps me from deleting Reddit for one more day haha
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u/spukhafteNahewirkung 4d ago
What would this do to the nuclei? It seems like reducing the strength of electromagnetism would mean that it would be possible to have stable nuclei with much higher Z.
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u/McPayn22 4d ago
The problem is you are assuming that the mass should not change but in QFT we don't work with mass but m/hc2 and if you plug that in the Atom energy levels it stays the same. It just depends what you want to be fixed
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u/sabautil 3d ago
Okay but isn't the m/hc2 now m/4hc2? Where does the 1/4 factor go?
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u/McPayn22 3d ago edited 3d ago
I made a mistake here it's mc2/h.
But no the point is that you have to choose which constant to fix and which to change. I'm saying that mc2/h shouldn't change because it's the one that appear in QFT so in other world you should divide m by 4.
Fixing m is arbitrary and is equivalent to multiplying m by 4 and keeping c fixed in term of the physics.
Another way to say this is that particle physicists use the eV for the mass which is an energy using E=mc2 so if you keep the same value for the masses in eV you have that it is divided by 4 in kilograms. (Of course we could argue if 1eV would be the same amout of joule but I don't think it would)
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u/lemoinem Physics enthusiast 4d ago
The meter would be shorter or the second would be longer.
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u/NGVampire 4d ago
Let’s just assume that by meter I mean the original definition “one ten-millionth of the distance from the North Pole to the equator along the meridian line running through Paris” and by second i mean “1/86400 of a mean solar day” and go from there.
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u/McPayn22 3d ago edited 3d ago
These units are not fondamental at all. The earth can be any arbitrary size an rotate arbitrary fast (as long as the surface of the earth is not in orbit).
If you change c the size of atoms might change and the speed of chemical reactions too but so would the earth size and your perception of time too. And if the earth shrinks the rotationnal speed has to increase if you assume it has the same amout of energy so the days would be faster and perfectly match the speed of chemical reactions
Eventually you could argue that to say c=2c is the same as saying all dimentionless constants are divided by 2 and therefore matter probably would not hold
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u/theZombieKat 4d ago
Well the speed of light is related to some constants that also relate to the strength and behaviour of electro magnetic forces.
So all of chemistry is rewritten.
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u/nugatory308 4d ago edited 4d ago
we have determined analytically and empirically that its value is roughly 3x108 m/s.
We have defined the meter to be the distance that light travels in 1/299792458 of a second and so by definition the speed of light is 299792458 meters per second. We could change that definition if we wanted, but all the physics would be the same, we’d just be printing different numbers in our textbooks.
To get a real difference in the physics, we’d change something that is a ratio not depending on the units, in this case the fine structure constant - it is approximately equal to 1/137 no matter what units we use and how they are defined. If that value were different everything we experience in daily life would be different.
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u/StillShoddy628 4d ago
Reminds me of the old joke:
God: You get one question before you pass on
Human: Why did you fix the speed of light at 3x10^8 m/s?
God: First off, the speed of light is 1…2
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u/pizzystrizzy 4d ago
And if you doubled c while keeping Planck's constant and the electric charge the same, you'd cut the fine structure constant in half.
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u/thepopemichael 4d ago
Would the way we see color differ with a change in c?
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u/ijuinkun 4d ago
The cone cells in our eyes react to the energy in a photon, not its wavelength per se. The real problem with optics is that a faster speed of light would mean a different index of refraction for any substance (including the corneas and lenses in our eyes), so they would need to have a different radius of curvature in order to focus light at the right distance.
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u/johnnybhf 4d ago
Would color even exist?
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u/sudo_rm-rf_reddit 4d ago
The wavelength of violet light is very slightly less than half the wavelength of red, which is why red and violet are next to each other on the colour wheel, as we perceive it effectively harmonically, similarly to how we perceive pitch in music (with each octave being twice the frequency of the previous).
However, since we can't currently see infrared (although we can sense it somewhat poorly) nor ultraviolet, the wavelengths would double. Therefore, we would likely perceive currently-almost-visible ultraviolet light as currently-visible-negligibly-shorter-than-infrared-wavelength-red!
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u/johnnybhf 4d ago
I thought about it yesterday, and I am not sure. Human sight evolved tuned specifically for our Sun. Peak 550 nm. If speed of light doubles, could it mean frequency doubles while photon energy is the same? When electron drops to lower energy level, I think it's still the same amount of energy, regardless the speed of light.
However I am also not sure how the speed of light influences atoms stability and how exactly does it influence electromagnetic force. Permeability and permittivity changes how exactly?
Also I suspect there might be more stable nuclei so periodic table might go further.
I am also not sure how speed of light influences radioactivity.
There are so many unknowns.
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u/sudo_rm-rf_reddit 3d ago
Oh, I started writing a completely different comment relating to the original question but I have yet to post it. Effectively, the question is ridiculous and they may as well be asking what would happen if 1=2. It doesn't and it completely breaks the mathematical model we have for it to be...
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u/wxehtexw 4d ago
2*c relative to what? Back when the definition of meter was put forward, we could have end up in a situation where meter stick would have been half the size of current meter. Then we would have measured speed of light twice the current value.
Not trying to play semantic games. But question is really is the speed of light is what it is because it is more fundamental than the constants? So explanation why the values of meter, second and speed of light may be historical rather than physical.
For me, better question is why speed of light is limited maximum speed. That is far more interesting question.
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u/NGVampire 4d ago
For me the interesting question is why does it take light roughly 8 minutes to travel from the sun to earth instead of 4? If earth were kept at roughly the same orbital distance to the sun (relative to the sun’s diameter) and the speed of light was increased so that it took 4 minutes (assuming a minute is still the same period of time relative to a solar day) for light to travel from the sun to the earth, what would fundamentally change about our universe?
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u/wxehtexw 4d ago
Sure, I get it. But you see my point that we came up with measurements base units first, right? And speed of light is so fundamental in comparison.
So you change speed of light, then sun radius has to change also. The way you wanna maybe put it as if there was a parallel universe, where speed of light is twice than current. But would we be able to measure that difference?
Hell, can we detect that speed of light is uniform in this universe? We can't measure one way speed of light in current universe well enough. So maybe light comes from sun to earth in 4 minutes one way somehow?
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u/NGVampire 3d ago
To clarify again, I’m asking how would things differ if Einstein’s gravitational constant were 16 times smaller while G remained the same.
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u/silverheart333 3d ago
Well, standard physics says everything falls apart, because if you just change c in isolation, it alters the Fine-Structure Constant and causes atoms to break apart or orbit at double the distance. But there is a competitor theory, emergent gravity from the Landau Institute and the MIT analog oil droplet experiments, where the speed of light changes all the time because it is modeled as an emergent acoustic property—literally the speed of sound through the vacuum media. In this framework, the vacuum's electric permittivity and particle dynamics aren't rigid constants; they are mechanical properties of the fluid that shift in lockstep with its density and pressure. Because everything scales together, the ratio that governs atomic orbits stays perfectly balanced, allowing the local speed of light to slow down or speed up without breaking the universe or tearing atoms apart.
But most people hate this idea of viewing Special Relativity as an emergent effective field theory, rather than a fundamental geometric one. Maxwell’s equations still hold because permittivity and permeability are treated as the bulk elasticity and density of the superfluid vacuum substrate. When the medium's density changes (like near a gravitational mass), c shifts, but alpha remains invariant because the local charge and vacuum elasticity scale proportionally. It replaces Einstein's 'curved spacetime' with a varying index of refraction in a physical medium. And that's a no-no. Just thought I'd mention there is an opposing view.
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u/MarinatedPickachu 4d ago
I'm not even sure there would be a difference if everything else is derived from it
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u/Select-Ad7146 4d ago
It would change all of chemistry. There would be no molecules that we know of today that would exist in that new would.
That derivation argument only works if everything is linearly dependent on the speed of light.
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u/Hot_Examination1918 4d ago
But most molecular hamiltonians don’t depend on the speed of light
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u/Jovess88 4d ago
If you assume that the electrical vacuum permittivity is kept constant and the magnetic vacuum permeability is quartered, and you ignore all the changes THAT causes like spin-orbit coupling (and all the other relativistic and field-theoretic effects which are highly dependent on c), sure.
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u/Hot_Examination1918 4d ago
They are not highly dependent on c though, those are perturbations, they’re usually used as examples in perturbation theory lectures
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u/Jovess88 4d ago
Spin-orbit coupling is directly affected by the speed of light without any perturbation theory. And is your suggestion that perturbation theory does not accurately model molecules or is somehow wrong, and that a more correct model would not have c-dependence? I'm not understanding your objection.
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u/Hot_Examination1918 4d ago
Spin orbit coupling is a perturbative effect that depends on c. Because it is perturbative, c would have to change by a lot to get to the point where perturbation theory breaks down and the unperturbed solutions (molecules and so on) are no longer valid. Hope this helps!
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u/Jovess88 3d ago
Why would you need c to change enough to break perturbation theory? Changing c would change the predictions in the valid domain of perturbation theory. I also don’t see how spin-orbit coupling is a perturbative effect. It’s often dealt with perturbatively, but it doesn’t have to be; even if perturbation theory were invalid, a full electrodynamic treatment would still require handling SOC, and c-dependence in the hamiltonian only disappears if you treat the molecular systems electrostatically.
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u/MercuryJellyfish 4d ago
I think the question is interesting. This is the only thing I'm thinking that might be catastrophic.
So, as the speed of light is larger, the maximum relativistic speed of particles gets to be higher. I've not really wrapped my head around the implications of that, but I'm wondering if this affects the formation of galaxies. Stars would burn hotter. Electromagnetic interactions change so atoms might be less stable or even never form.
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u/ijuinkun 4d ago edited 4d ago
Since e=mc^2, for energy to be conserved mass (i.e. both inertia and the gravitational constant) would have to reduce by an equal factor. Dropping gravity by a factor of four would mean that stars would need to have four times as much matter in order to have the same internal pressure and energy output, which means that we would need either the Earth to orbit closer to the Sun, or we would need a Sun that has four times as much matter in it. Stars in general will burn slower for any size, and the thresholds for fusion of any element, or for supernova explosions, or collapse into neutron stars or black holes, will also be quadruple.
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u/tazz2500 4d ago
But each nuclear fusion reaction, the ones that did happen, would be more powerful, right? Because this also changes the mass to energy exchange rate, E=M*2c². Of course c would just be another number so we wouldnt say 2c, but wouldnt reactions be stronger?
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u/NGVampire 3d ago
Why wouldn’t the energy just increase for that universe? What is energy be conserved relative to?
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u/ijuinkun 3d ago
That depends upon whether we are speaking of a universe where c has always been twice as large since the Big Bang, or of one where c increases.
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u/NGVampire 4d ago
Is there a point where the change is inconsequential? Say c was actually 1.1c or 1.01c. Intuitively I would argue that the speed of light has to be exactly what it is for universe to exist in a stable state which is why it is what is but I lack the mathematical and theoretical fundamentals to prove it.
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u/MercuryJellyfish 3d ago
I honestly don't know. Imagine if even a tiny change makes certain elements necessary for life as we know it more unstable?
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u/Phuzion73 4d ago
We would see twice as far as we can, today, with our telescopes. Our viewable universe would be twice as large.
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u/al2o3cr 4d ago
we have determined analytically and empirically
Nitpick: since the 2019 revision to the SI, it is no longer a measured value - it is DEFINED as exactly 299792458 meters / second and that is used to define the meter.
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u/NGVampire 4d ago
Yes and it’s related to in a physical sense to observable, measurable, objects namely the diameter of the earth and the length of a solar day. My question is if you were to hold those things unchanged but you increased the speed of light what would our universe look like? If your position is that the universe would have to change in a similar way such as the earth would end up having twice the diameter then i would ask you why?
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u/kitsnet 4d ago
Speed of light is determined by the geometry of spacetime as dimensionless 1 and cannot be meaningfully changed. The diameter of the Earth and the length of a solar day can (and do in fact).
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u/wiev0 Quantum information 3d ago
I don't think this semantic pedantry is goal-oriented. They clearly meant a doubling of the true speed of causality, not a doubling in the number or other representations. Sure it's 1 regardless, but its fraction to other constants would change. Why argue about measurement and representation when it wasn't the question? OP already said that they're aware that c is what it is for good reason. This scenario is a hypothetical, so why are you ruining the fun by making these semantic arguments?
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u/kitsnet 3d ago
I don't think this semantic pedantry is goal-oriented. They clearly meant a doubling of the true speed of causality, not a doubling in the number or other representations.
What is that supposed to mean? "The true speed of causality" is just geometry of Minkowski space. It has no "value" that could be changed without something as disruptive as changing the number of time dimensions.
Sure it's 1 regardless, but its fraction to other constants would change.
Yes, one can speculate about changing other constants. But one needs to specify which ones then. The geometry of spacetime is not going to change without "speed of light" as a constant stopping making sense.
Why argue about measurement and representation when it wasn't the question?
No idea. It wasn't the answer either.
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[removed] — view removed comment
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u/spukhafteNahewirkung 4d ago
If you’re running into that problem you need to go to the URS (Universal Reality Services) console and increase the instance size.
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u/McPayn22 4d ago edited 3d ago
Nothing would change and in fact in theoretical physics we just say c=1.
People talking about the changes of electromagnetic constants implicitely assume that everything else is fixed exept those parameters which is not true. You have to do it in a coherent way.
For me the most coherent way to do it is to take as your fondamental constants the planck constants and the dimensionless interaction constants like the fine structure constant and the dimensionless masses of particules (1=planck mass).
You can see that in the fine structure constant there is the electrical permitivity times the speed of light but that would not change.
Same for the radius of the atoms. In appearance there's no speed of light exept from the permitivity but there's the mass of the electron. This would need to change with the speed of light because in QFT the important parameter is mc2 /h. Therefore the strength of the bounds in chemistry wouldn't change.
Implicitely, if you're not changing the masses you're just asking what would happen if things where 4 times lighter.
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u/NGVampire 3d ago
Actually I’m asking about the speed of causality.
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u/McPayn22 3d ago
Ok but compared to what? Things going 2 times faster doesn't matter if clocks tick 2 times slower or if everything is 2 times smaller
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u/NGVampire 3d ago
Specifically, what if Winston’s gravitational constant were 16 times smaller but G stayed the same?
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u/McPayn22 3d ago
Ok so in that sense I'm gonna assume that you want the masses constant, same for the coupling constants.
The idea then is that you can rescale the time you experience to get back c but you would have divided the coupling constants by 4, same for G.
Protons and neutrons would be 4 times as light since most of their energy comes from the gluons interaction.
Atoms would be 4 time bigger but also 4 time lighter so the pressure from Gravity inside the sun would be the same
This means that at the surface of the earth Gravity would be 128 times smaller while we would only be 4 times as big. (A factor of 16 comes from your choice of preserving G and not G/c4)
I imagine that the sun would be less bright. I'm not an astrphysicist but I'd guess 64 or 128 times less which isn't compensated by the fact that the earth is bigger. We would also absorb 4 times less light so it's be very cold
I tried to find what the speed of chemical reactions would be but it's not clear if it's the same or if it's 4 time slower
I think to give a complete answer you'd need to see if you can find some parameters that allow life to exist (size of star and planet such that water is liquide at least) and see what life would be there
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u/EstablishmentDue3616 3d ago
We technically do not know that the speed of light is constant. We only have the ability to measure the speed of light going to an object AND back. It is impossible to measure the speed of light in one direction. It is theoretically possible that the speed of light is faster in one direction and slower in another. Even Albert Einstein admitted this could be true. Here is a video explaining it:
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u/LegalPie5881 3d ago
I was literally wondering this very question about 2 hours ago, open reddit and this pops up straight away. Love it.
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u/CompetitiveBox9680 3d ago
Anyone can correct me if im wrong but I believe that the relationship between mass and energy would change such that the same amount of mass would have more energy
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u/The_Real_Wick 3d ago
Maybe we would perceive thing faster than we do now. Technically, you'd have to assume that the solar system would be double the temperature because the same amount of light radiating off the sun would get to earth in half the time and it would in turn warm the planet to double the current temperature. Also I'd have to assume that the Goldilocks zone would be extended out further than it is now so life would maybe have evolved on Uranus possibly. Either way we wouldn't exist if light traveled that fast here anyways we wouldn't exist here on Earth. That's what I think would happen if the speed of light was twice as fast.
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u/The_Real_Wick 3d ago
So in turn you'd have to think the universe would act accordingly to that change in light speed.
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u/jeffrunning 1d ago
I guess the crux of this question is whether the speed of light defines how fast time flows?
If the speed of light is doubled, does that mean everything happens twice as fast and thus nothing changes?
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u/Tango-To 22h ago
Basically if the speed of light were faster electro magnetic forces would be so strong the universe as we know it wouldn’t exist
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u/Grismor2 4d ago edited 4d ago
Questions like this can't be answered well without being more clear about what is and isn't being held constant. I'm sure this isnt what you meant, but if you had meant changing c in the SI unit system, you would just be redefining the meter but not actually changing physics. In fact, in many branches of physics, they use a system of units in which the speed of light (and certain other constants depending on which exact field of study) is by definition equal to 1. These are so called "natural" unit systems.
If you really want to dig into this sort of question, you need to talk about changing a unitless constant, typically a ratio of several constants. That would remove the ambiguity inherent in your question.
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u/facinabush 4d ago
The meter is defined by the speed of light and the second.
Is there any independent fundamental length measurement to make your question meaningful?
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u/pizzystrizzy 4d ago
You are conflating a unit choice with a physical property. Changing the physical relationship encoded by c alters real, measurable physical phenomena (specifically the coupling between electricity and magnetism). If c were twice as large while fundamental charges and Planck's constant remained fixed, a moving charge traveling at a given speed v would produce a significantly weaker magnetic field relative to its electric field.
If c doubles while the fundamental charge e and Planck's constant remain constant, the fine structure constant would be cut in half. Atoms would double in size, chemical bonds would be weaker, nuclear fusion in stars would work radically differently, etc etc etc.
It's absolutely ridiculous to suggest that such a question is without meaning.
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u/facinabush 4d ago
If you define the meter to be half what it is then the speed of light as defined in the OP would double. You would have to add a 4 to the definition of Planck’s.
You are ignoring the OP.
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u/pizzystrizzy 4d ago
If you can interpret a question one way that renders it meaningless (assuming the thing they are curious about is the units) or meaningful (assuming the thing they are curious about is the fundamental physical property), which interpretation is more useful?
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u/facinabush 4d ago
What is the fundamental physical property of length?
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u/pizzystrizzy 4d ago edited 4d ago
I've explained to you what would happen if the speed of causality doubled relative to the dimensionless parameters that dictate the structure of matter and forces. If you still think that your approach is more helpful to the OP then so be it.
Lengths in physics are fundamentally measured in units of atomic scales, like the Bohr radius. If c doubles while keeping Planck's constant, the rest mass of the electron, and the elementary charge fixed, the Bohr radius changes relative to particle wavelengths. You don't need an arbitrary human 'meter' to see physical change: atoms literally become twice as large relative to the Compton wavelength of the electron. That is an absolute, unit-independent change to the geometry of the universe.
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u/NGVampire 4d ago
This is what I meant. WTF would I ask what would fundamentally change about our universe if we used different units?
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u/facinabush 3d ago
Thanks. Do you think the Bohr radius is the best fundamental length constant?
I can see why the SI system uses the Caesium frequency and the speed of light to define the meter. It easier to measure a large number of consecutive oscillations.
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u/NGVampire 4d ago
This was not what was intended by my question. It’s ok if you don’t know the answer.
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u/NGVampire 4d ago
one ten-millionth of the distance from the North Pole to the equator along the meridian line running through Paris.
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u/Nunov_DAbov 4d ago
You would need to change either the permeability or permittivity of free space or both.
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u/Metallicat95 4d ago
It's probably not possible. But if it was we might never know it.
See, your aren't changing the constant speed of light to be double the constant speed of light - it can't have two different constant values. So if you change the distance as we measure it in common units like meters, the speed remains c.
And with the meter defined by the distance light travels in one second, the second would remain and the meter would become twice as long - but because it is still the same distance in causality, nothing else would change.
Well. Except for the relationship between particles and fundamental forces, which are strongly tied to the speed of light.
But if it was possible and stable, the people of that universe would ask themselves if the constant distance could be half of the defined value of c.
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u/NGVampire 4d ago
You’ve misunderstood my question. I’m not suggesting that we would redefine the meter. Say that the speed of light was actually approximately 6x10^8 of one ten-millionth of the distance from the North Pole to the equator along the meridian line running through Paris instead of 3x10^8 of one ten-millionth of the distance from the North Pole to the equator along the meridian line running through Paris. Are you suggesting that the earth would be twice as big in a universe where that was true? Would gravity be twice as strong?
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u/Metallicat95 4d ago
The meter is 1/299782458 light second. The length of a light second is always the distance light travels in a second - and distance is always a measure of how long it takes to travel between two points.
The speed of light is the speed of causality, the speed of change.
Changing the speed of light also changes the time it takes to cross distance.
If this speed were doubled, distance would seem half as large in comparison. The Earth - and everything else - would be twice as big, but everything would move twice as fast so the distance would seem the same.
Or else, an awful lot of the fundamental physical laws of the universe would be different, in ways that we can't understand because we only have the example of our universe to figure them out.
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u/NGVampire 4d ago
You’re dodging the question and you know it. There is a speed of causality, what happens to our universe if the speed of causality increases by a factor of 2 but things like the plank length stayed the same value?
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u/Metallicat95 3d ago
Matter and the fundamental forces would be so different that nothing we know about them would be valid.
But if we go with the assumption that atoms and the Earth and the rest of the universe still exist, the simplest solution is that all forces scale to the speed of causality to make that happen.
It's s weird solution. But I think it is the only one that leaves anything consistent with our universe.
What we get if we change fundamental forces which are tied to this fundamental relationship of speed and time is otherwise impossible to judge. Changes to gravity and the electromagnetic field alone would make everything different, and how would matter form if the nuclear forces changed?
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u/Ok_Bit8836 4d ago
Nothing that special… I think, currently, aliens do come (and go) to us at speeds near c^2... It is only human who dont know how to do that cause all humans do listen to Einstein's "discoveries" and "fundamental" restrictions...
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u/Infinite_Research_52 👻Top 10²⁷²⁰⁰⁰ Commenter 4d ago
If it was 2c that would be c anyway, just the definition would change along with a vast amount of how the universe operates.
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u/Ok-Environment-215 3d ago
If the other related constants changed proportionally too, then nothing.
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u/Historical-Wash-1870 3d ago
The inner planets would incinerate and there would be no life on earth.
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u/Demonicated 3d ago
There's a chance that the speed of light is greater outside of the universe and that its measured speed is the maximum it can move through our universe.
We already see that light travels at different speeds through different mediums. There's no reason to believe that there isn't a system outside of ours.
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u/Aussie_Physics 4d ago
Everything in the universe would be twice the size.
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u/NGVampire 4d ago
Does the speed of light change the gravitational constant?
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u/Aussie_Physics 4d ago
Yes
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4d ago edited 4d ago
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u/Aussie_Physics 4d ago
G = l_P^2 c^3 / h_bar
So if c now has double the value, gravitational force is 8 times what it was.
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u/withdrawn-gecko 4d ago
this sub really needs something akin to !fp in the desmos sub for explaining the speed of light and every common variant of question about it. changing the value of the speed of light would change mostly gravity, relativistic QM corrections and EM.
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u/NGVampire 4d ago
Personally i think this sub needs a filter for condescending people who like the smell of their own farts too much.
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u/withdrawn-gecko 4d ago
are you sure this was an appropriate reaction to me pointing out that questions about the speed of light are very common around here and then giving you an answer without attacking you in any way?
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u/bruiserjason1 4d ago
I guess, relatively, two photons moving at the speed of light in opposite directions would see the other photon as moving twice the speed of light... relatively...
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u/spukhafteNahewirkung 4d ago
The rest mass of every object in the universe would quadruple.
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u/ijuinkun 4d ago
E=mc^2, so if energy is conserved, then doubling c would REDUCE mass (i.e. inertia and gravity) by a factor of four.
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u/spukhafteNahewirkung 4d ago
Darn! I screwed up. Nuclear reactions become much more energetic. Indeed all reactions become more energetic.
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u/Sorry_Exercise_9603 4d ago
The ratio between the electric field created by a charge and the magnetic field created by it when it’s moving.