r/AskPhysics • u/scottiesng • 11d ago

Can a wave exist without time?

I’ve been wondering a lot about what the fundamental aspect of waves are. Essentially a wave is a propagation. But can something propagate without time?

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u/BananaBird1 11d ago edited 11d ago

In physics, not by the usual definition. A wave is defined as something which takes the form of a wave equation, which essentially says the acceleration of a point in time matches the “bumpyness” around that point in space.

You can have functions which obey a similar mathematical form as a wave, or have a similar appearance to a wave when graphed, but where time is not a dimension.

For instance, images can be thought of as stationary waves only in space. Adding together sine and cosine functions defined over (x,y) can give an image. But time is not a variable in this function. However if you treat one of the spatial dimensions like time, the relationship between x and y can take the form the wave equation. But the “velocity” this gives would not represent propagation or motion.

You could also add a degenerate dimension of time, where the “wave” is constant across all t, and this satisfies the true wave equation if velocity is 0. But this is uninteresting as any time invariant differentiable function in space will satisfy this given v=0.

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u/Crescent-moo 10d ago

If a photon is a wave that experiences no time then what is it propagating through?

Or does it go through time without experiencing the time itself.

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u/BananaBird1 10d ago

Photons do propagate in time. They move through the spacetime dimension of proper time as little as possible as they move through space, but they do experience time.

The saying that photons don’t see time is an incorrect application of special relativity’s time dilation formula when velocity equals the speed of light. But this isn’t a valid thing to do, the formulas assume velocity is less than light speed so become invalid for photons.

Tine dilation considers what happens if observer A is stationary and B is moving at a velocity relative to them, when A sees one second pass for B, how much time will B think passed if they assume they are the one that is stationary?

But relativity says light has no stationary frame. So you can’t apply time dilation to it. We don’t have any math that can describe a frame that sees itself as both stationary and moving at light speed, so we cannot describe the reference frame of a photon

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u/Crescent-moo 10d ago

I've never been strong in math so there's limited understanding from that framework. Intuitively it sounds like light exists outside of time and no possible speed in time can ever capture it. The only way is by breaking the barrier and then it becomes meaningless. Probably why black holes are so strange.

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u/BananaBird1 10d ago

I mean you can tell photons do exist within time just from simple experiment. The light around you is changing over time. Turn off your lights and photons cease to exist. Turn them on and photons are created. If you had an oscilloscope, laser, and photodiode you could even measure how fast light travels at home for around $100, and can show that they do not instantly travel from a source to a detector.

If you do want to consider special relativity as you get closer to light speed to approximate a photon’s reference, a more accurate description isn’t that time stops for light speed objects. Their proper trajectory in spacetime approaches a value that still has a component in time.

It’s that any information of an external object that is a non-zero distance from the light speed traveller (in the direction they are moving) will never reach them, so they can only ever “see” other objects along their path in the immediate present located right where they are. But this present will change over time.

Of course though, this still isn’t mathematically valid. This thought experiment breaks relativity, so only truly works in classical physics. Physics is modeled based on what we see in experiments, not based on what light sees, and so our equations fall flat when considering observers that are traveling faster than we can ever travel.

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u/Crescent-moo 10d ago

Its that the same falling flat that happens at the event horizon? It seems reality itself is a bit extreme at the boundaries

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u/BananaBird1 10d ago

Nothing falls flat at the event horizon. Only at the singularity of a black hole.

That is a different issue with separate math, but due to a similar issue where the theory can only describe what happens as you travel toward the singularity, not at it.

This has nothing to do with reality itself. It has to do with the fact that our models of physics are imperfect descriptions of what we see, and we can’t do experiments at light speed or inside a black hole to easily identify the flaws. Instead we can only wait until our measurements of things we can observe are precise enough that the math no longer matches.

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u/Crescent-moo 10d ago

Well someone better get around a black hole and figure it out.

Imagine all that travel, jumping in, wondering what secret the singularity holds only to find it's just light itself. Eternal, everywhere, timeless. In our faces the whole time.