0

First of all, I've read almost all of the similar questions and duplicates given under them. And the question is never answered properly in any of them so please don't just share duplicates and leave it at that. The question is, is there a theoretical mechanism that explains why $c$ has the value it has? Is there a mechanism (even a proposed one) to explain this?

Before anyones says it, yes I would still ask this if $c$ was $1\frac{lightseconds}{second}$ ie. described in natural units. Regardless of the numbers and units we assign to it, speed of light has some intrinsic value. Whatever we define it to be, it takes 4 full rotations of Earth around the Sun for a beam we send to reach Proxima Centauri, which is about 4 lightyears away.

Yes, I know that speed of light isn't something unique about light or photons and that any massless particle in our universe travels in this speed. This doesn't answer anything about the question, just a fancy way of saying "it just is". I don't even know why some users gave this as an answer in other threads.

$c^2 = \frac{1}{\mu_0*\epsilon_0}$ is not a proper explanation because

  1. any massless particle has a speed of $c$, not just photons.

  2. this relation is just a consequence of special relativity in its core, which has no mechanism explaining the origin of $c$.

This is just one of its assumptions which is validated empirically.

It seems to me that this is just an observation at this point with no known mechanisms behind it to explain it. If so, what are some likely and popular proposals for such mechanisms?

edit: People are once again trying to explain why the value of 310^8 m/s is an arbitrary one similar to 1 mile = 1.609344 kilometers. Once again, these numbers and units are of course arbitrary and are just tools to convey the idea. I am not questioning the value of 310^8 m/s. It could have been 42 sticks/mississippis or 1 ls/s.

Yet the amount of time it takes for a photon to travel from the Sun to Earth isn't arbitrary is it?

Qmechanic
  • 220,844
GUNDOGAN
  • 367

3 Answers3

6

The answer is that we don't yet know why the speed of light is what it is (leaving aside the question of the units in which you might choose to express it). The same can be said of many of the other building blocks of physics. For example, we cannot yet explain why an electron has a specific mass and charge. In physics we can explain complicated objects and phenomena in terms of their simpler components, but there is a point beyond which we cannot provide explanations about why things are as they are.

Professor Sushing
  • 29,350
3

I think that @JohnDoty's answer may be closer to the mark than you expect. The missing concept is that time and space are much more alike than you think. They are so much alike that they are treated as different directions in a single $4$-D spacetime. So asking why $1$ lightsecond is the same as $1$ second is much like asking why $1$ lightsecond east is the same as $1$ lightsecond north.

The deep relationship between time and space is more than light travels $1$ lightsecond of distance in $1$ second of time. I have tried to explain the relationship in my answer to Euclidean space to Minkowski spacetime

That explains why there is a relationship between distance light travels in a time interval and that time interval. But you are asking if there is a mechanism to explain why it has a particular value. Perhaps another way to get at it would be to ask what would break if the speed of light had a different value.

The answer, as @MarcoOcram said, is we don't know. People have looked at how physics would change if various values were different. Perhaps life would be impossible, but we don't see any reason that physics wouldn't be self consistent. It just wouldn't explain the universe we see.

Here is a link to a rather speculative idea that the laws of physics could be different if you go far enough, beyond what we can see. The Multiverse, Science or Science Fiction? | Sean Carroll

Perhaps the problem is that you are asking why the universe is as it is. Physics doesn't answer "why" questions, except that more complicated answer are the results of simpler answers. It cannot explain why the simplest answers are as they are.

mmesser314
  • 49,702
1

Why did mariners historically use different units (fathoms and nautical miles) for depth and distance? It's because they were using different instruments to measure them, and also because the concerns (running aground versus crossing oceans) involved very different scales.

Similarly, we have historically used different instruments for measuring distance and time in physics. But we now have a well-tested principle that the speed of light in a vacuum is fixed. That opens up the possibility of using a clock as the basis for distance measurement, and for the past half century that has been the most reproducible way to measure distance. Thus, the speed of light is now an arbitrary defined constant.

But why is it so big? That relates to our human concerns about space and time. Meters and seconds are units that match the scale of our experiences: 1 m/s is a comfortable walking pace. Generally, the velocity dispersion of matter in the universe is well below the speed of light, and the velocity dispersion of macroscopic objects on Earth is extremely low. Biology as we know it would be impossible if this wasn't true.

John Doty
  • 22,119