# Why is there a speed of light? **URL:** \ **Category:** Factual Questions\ **Created:** [October 5, 2015, 8:30pm UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639 "2015-10-05T20:30:01Z")\ **Posts on this page:** 5\ **Page:** 4
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [October 8, 2015, 10:03pm UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639/61 "2015-10-08T22:03:44Z")
Because everything would already be done and over if it were infinite? ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [October 11, 2015, 11:03am UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639/62 "2015-10-11T11:03:45Z")
> [@Chronos](#): > > **Melbourne** , you are using the word “mass” in a different way than it is used by physicists. I can’t blame you for that, since unfortunately a lot of physics textbooks do the same thing, but when physicists say “mass”, we mean “rest mass”. Well, I was taking my key from the original post, which I didn’t take to be a question from a physicist. So I won’t blame you for using a physicists definition, even if that obscures the answer. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [October 11, 2015, 9:30pm UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639/63 "2015-10-11T21:30:48Z")
> [@Asympotically\_fat](#): > > Imagine you have a telephone that you can phone and alien in another Universe with. Luckily he speaks perfect English (with a heavy Zfolgian accent) and is au fait with scientific concepts. From speaking to him about physics he describes the theory of relativity, except he describes c as 2.6 vlargs. Is there any experiment you could ask him to perform that would determine whether c is different in his Universe or if he is just using different units to describe the same c as in our Universe? The answer is no there isn’t… > The speed of light through some medium depends on the properties of the medium, so it is no different from describing those properties of the medium. Neatly put. I like. > [@Saint\_Cad](#): > > That is not the question!!! > Why does light travel at the rate it does. It has nothing to do with units of measures and everything to do with the concept of “faster” and “slower” which independent of units of measures. This is a physics question - not a metrology question. > > Why does light travel at the velocity it does and not a different velocity. And don’t give me the crap about “it could if you change the units.” I am asking why is light not faster or slower than it is now. If you are talking about units and defining meters and seconds defined as vibrations that would scale with c or anything like that you are missing the point of the question. I know by correct SD custom OP always gets to be the first to get cranky in “his” thread, and allowing for the fact everybody knows you, sort of, as a normal person interested in physics, and you’re using hyperbole and being silly and all, quintuple exclamation points and “don’t give the crap about” seems pretty borderline. I think I’d get buried if I did it…🙂 ---
**Author:** ![Measure\_for\_Measure](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/measure_for_measure/32/557_2.png) [@Measure\_for\_Measure](https://boards.straightdope.com/u/Measure_for_Measure)\ **Post date:** [October 13, 2015, 12:34am UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639/64 "2015-10-13T00:34:59Z")
> [@Cyros](#): > > I’m much too dumb to have anything but the most rudimentary understanding of any of this but thought I’d share this [video](https://youtu.be/msVuCEs8Ydo) that made a timely appearance in my feed today. It goes through the math of why the speed of light (or causality if you prefer) is what it is. I thought it was a good explanation as my non-math mind could actually catch a glimpse of what he was saying. This non physicist liked that 10 min presentation as well. I can think of a couple of other ways of addressing the OP. (I’m using a counterfactual approach.) Why is there a speed of light? Or… what would happen if the speed were infinite? Why is there a speed of light? Or… what would happen it it was half as fast? Would we perceive a larger or smaller observable universe, assuming that the big bang occurred X years ago? Why is there a speed of light? Or… what would happen if its velocity were additive? (A: Competing reference frames, right?) Why is there a speed of light? Or… what would happen if it fluctuated over time? Why is there a speed of light? Or… what would happen if there were no massless particles? ETA: I’m guessing that one of the answers to most of the above would be: “You would not be able to ask that question.” ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 13, 2015, 2:04pm UTC](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639/65 "2015-10-13T14:04:02Z")
If there were no massless particles, at least, the difference would be “not much”. We’re not even certain that there are any massless particles in our Universe. All of our observations could be equally well explained by assuming that photons (and gravitons) have a mass that is just very, very small. It would make the math describing them a bit more complicated, but since when has the Universe ever cared about that? [Previous page](https://boards.straightdope.com/t/why-is-there-a-speed-of-light/733639.md?page=3)