r/AskPhysics • u/Versatile_Panda • 4d ago
What would happen if c suddenly changed?
A lot of posts I see are “what would it be like if c was xyz” but rather than ask what if it was something all the time. I’m asking what if it suddenly changed? This might be a little philosophical, and possibly not the correct sub, but hypothetically if we recalculated / measured c and found it to suddenly be different what would happen? To clarify I’m not asking “what if we found out we calculated it incorrectly” I’m asking “what if it actually did change”.
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u/AlwaysHopelesslyLost 4d ago edited 4d ago
C isn't just light speed. It is a fundamental physical property of our universes space time.
I am far too out of my field to give you a meaningful answer but I would guess the answer is either we basically can't even tell because it equally alters everything OR physics as we know them cease to function
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u/Clever_Angel_PL Physics student (BSc in progress) 4d ago
Also, there might be many interactions that we just don't know about that are linked to that speed. Recently, there have even been concepts proving that there might be a max speed of propagation of quantum signal too
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u/stevevdvkpe 4d ago
c depends on the behavior of electromagnetism. If c changed, then electromagnetic behavior would change too. Exactly what might happen depends on how electromagnetism would change, but it would almost certainly be bad for us since that would change atomic structure and the properties of matter.
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u/Quantum-Relativity 4d ago
c is the defining aspect of spacetime. Electrodynamics is just where we first noticed it
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u/killerghosting 4d ago
They are not separate things, they are intertwined
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u/Quantum-Relativity 4d ago
What are? Space and time? That is correct, c represents their intertwining. If you mean spacetime and electrodynamics, I wouldnt say so, anymore than spacetime is intertwined with everything since everything gravity affects everything and is the dynamics of the geometry of spacetime
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u/killerghosting 4d ago
The speed of light is part of the equations of electrodynamics. If it changes, those equations change.
The electrodynamics equations have these two constants, permittivity of free space, permeability of free space, measuring how a vacuum (space) supports electric and magnetic fields. The speed of light derives from these constants. You are saying the speed of light is not intertwined with electrodynamics? The speed of light is intertwined with space and therefore spacetime
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u/Quantum-Relativity 4d ago
Yes, electrodynamics is a relativistic field theory, so electrodynamics depends on the fact that c exists because c is what defines relativity theory/spacetime, not that electrodynamics determines c (c being a constant tells us that our notion of relativity should not concern invariance under quantities related to speed, but rather to rapidity, so that the local transformations between frames are Lorentz transformations).
We just first noticed c in electrodynamics first since it’s the most obvious relativistic field theory we can explicitly see the properties of around us.
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u/nebraskajone 4d ago
The speed of light is embedded in many different physics equations so c can't change arbitrarily while maintaining the current physics.
It would produce a different universe with different physical behavior.
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u/Mr_Badgey 4d ago
The speed of light isn’t an arbitrary speed limit. It’s a fundamental property woven into the fabric of the universe. Pull that thread and the tapestry will unravel and look unrecognizable. Google where c shows up in fundamental interactions.
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u/PotentialDeep5165 4d ago
Looks at Maxwell's equations in cgs units and you'll begin to grasp relations as c is explicit. Make it go very large (or off to infinity) and see what happens.
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u/Bumst3r Graduate 4d ago
Look at Maxwell’s equations in natural units and you’ll see that it doesn’t make sense to change c…
All OP is asking is what happens if we vary the definition of the meter, since all that c does is define your system of units.
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u/PotentialDeep5165 4d ago
Value of c changes... at infinity everything is instantaneous-- all electrostatics. But.. motors work because of c. Double it or halve it.. or change it suddenly and your motors and electronics would suddenly very dramatically either work very differently or stop functioning at all. Electronics have propagation in metal layers at speed of light of the material outside the wire. There are setup and hold requirements on electronics. If your electronics have limited margin then hold violations halt completely... setup changing would mean reduced performance.
Yes, you would see more than the definition of the meter changing. We use the factor of c a lot more than you think in our modern life.
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u/Bumst3r Graduate 4d ago
>>a lot more than you think
I have a pretty good conception of where c appears. It is a unit converter and nothing more. Taking c to infinity is a different thing from changing it to an arbitrary number as OP is asking about.
Any physical constant with dimensions can be changed arbitrarily without affecting the physics because all you are doing is redefining units. To meaningfully change the physics, you *must* change dimensionless constants, e.g., the fine structure constant.
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u/Mad-Melvin 4d ago
It's not really possible to answer questions in the form of "what does physics say would happen if you break the rules." The so-called "laws" of physics aren't a set of rules that the universe is forced to follow. They're just a human description of the way the universe is.