# Why is light speed the limit? **URL:** \ **Category:** Factual Questions\ **Created:** [December 30, 2003, 10:48am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742 "2003-12-30T10:48:52Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![culov](https://avatars.discourse-cdn.com/v4/letter/c/e79b87/32.png) [@culov](https://boards.straightdope.com/u/culov)\ **Post date:** [December 30, 2003, 10:48am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/1 "2003-12-30T10:48:52Z")
Ive read a lot of books which include the speed of light for some purpose, many of which have the speed of light as a major topic, but i have never once read WHY the speed of light is the fastest that any object can travel. Why cant I just go ahead and say that 3.13x10^8 is the fastest anything can travel? thanks, culov ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [December 30, 2003, 11:00am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/2 "2003-12-30T11:00:31Z")
Light-speed being the limit that it is is a result of Special Relativity, and it comes from the two axioms of SR:[ol][_]The laws of physics are the same in all Inertial Reference Frames[_]The speed of light is the same in all IRFs[/ol]It takes a little math to get from these two statements to the idea that c’s the limit. Now, you might well ask _why_ these axioms are true. The first one (the so-called Equivalence Principle) does have a sort of aesthetic appeal, so you may be satisfied with it as is. But as for the second one - why should the speed of light be the same in all frames? Maybe someone else knows, but as best as I can tell, that’s just the way the universe is. ---
**Author:** ![culov](https://avatars.discourse-cdn.com/v4/letter/c/e79b87/32.png) [@culov](https://boards.straightdope.com/u/culov)\ **Post date:** [December 30, 2003, 11:09am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/3 "2003-12-30T11:09:11Z")
So those 2 statements are the basis? They both seem logical. Ill just go to the bookstore tomorrow and take a quick look at a book i saw on special relativity where im sure the math is completed. Would you happen to know how complex the math gets? thanks, culov ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 30, 2003, 11:13am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/4 "2003-12-30T11:13:18Z")
The speed of light is the maximum speed at which the universe can transfer energy or information from one place to another - if it were possible to exceed it, then there would exist reference frames in which effect could precede cause and all kinds of interesting paradoxes could occur. I think I’m right in saying that there is no such thing as a genuinely possible paradox. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [December 30, 2003, 11:18am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/5 "2003-12-30T11:18:15Z")
> [@](#): > > Would you happen to know how complex the math gets? Dude, words can’t begin to describe. Maxwell decided that even _complex_ math wasn’t up to it, and had to go and invent a whole new branch of math (sorta “ultra complex”) to deal with it. 😉 ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [December 30, 2003, 11:27am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/6 "2003-12-30T11:27:59Z")
Actually, the maths isn’t **that** bad. I mean, you wouldn’t be able to derive it unless your Einstein, but if you can do highschool maths you’ll be able to get to “speed of light is the limit” if it’s explained well. What’s really hard is beleiving it once you’ve proved it. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [December 30, 2003, 11:49am UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/7 "2003-12-30T11:49:59Z")
**Shade** , you’re a mathematician, right? Gotta take issue with you on a few things: 1. You failed to snicker at my “complex” joke. (In which I really should have said some thing like “Maxwell and Heaviside”, rather than just Maxwell) 😉 2. Twasn’t Einstein that derived it. Maxwell, Lorentz and Minkowski had more to do with it. Big Al was a contributor, along with Riemann, Stokes, Hertz, Poincare, _et al_. 3. It’s not something that can be “proved” in the mathematical sense. 🙂 ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [December 30, 2003, 12:39pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/8 "2003-12-30T12:39:56Z")
The answer to the OP is, that’s just the why the universe is. I am confused exactly what the “why” refers to, the posters have taken in the context of how was it derived/theorized. As for why the actual universe is this way, that’s just how it goes. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [December 30, 2003, 12:43pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/9 "2003-12-30T12:43:14Z")
Jeez. I forgot Karl. Big Karl Gauss - major contributor just prior to Maxwell on the on the electromagnetism thing, but also the dude who laid the foundation for the whole curved space-time thing that bacame Einstein’s _real_ achievement: general relativity. Special relativity is popularly attributed to Einstein, but it wasn’t really a big deal. Other people had already developed it to the point where it was pretty sure to become mainstream within a couple of years, with or without Einstein. Oh yeah the OP. 2.99792458x10[sup]8[/sup] ms[sup]-1[/sup] is just a measured value. You wanna postulate 3.13x10[sup]8[/sup]ms[sup]-1[/sup], go right ahead. It’s at odds with measurement, however. You wanna argue that it shouldn’t be a limit, take it up with Poincare. ---
**Author:** ![Sergio](https://avatars.discourse-cdn.com/v4/letter/s/b77776/32.png) [@Sergio](https://boards.straightdope.com/u/Sergio)\ **Post date:** [December 30, 2003, 2:01pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/10 "2003-12-30T14:01:44Z")
I think a more understandable way to answer the OP is that, according to the Theory of Relativity, the mass of an object increases with its velocity. When the speed equals that of the light, the mass becames infinite. There is no force capable to accelerate an infinite mass, so the speed of light is a limit. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [December 30, 2003, 3:48pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/11 "2003-12-30T15:48:39Z")
In layman’s terms, it works like this: E=mc[sup]2[/sup] means that matter and energy are equivalent, matter being a whole lot of energy stored in a particular small area, or energy being matter dispersed over a wide area. Lorenz demonstrated that this equation leads to the conclusion that something’s mass increases as it speeds up, its own sense of time dilates so that what should happen in a second by “standing still” rules will take substantially longer, and a bunch of other contrary-to-common-sense implications. (In a not-quite-on-target parallel, contemplate the difference between tossing a bullet to someone else with a flip of one’s hand and shooting the same bullet at him with a rifle. The same object, but the kinetic energy it carries in the second case produces remarkably different results. While this is force, not mass, being measured, it should enable you to grasp the idea better.) According to Lorenz’s equations, the difference is based on complex numbers involving the relationship of the velocity to the speed of light – what fraction of the latter the velocity is. Net result is that as the object approaches the speed of light, its mass climbs without limit – “becomes infinite” in layman’s terms. Therefore the amount of energy that must be supplied to accelerate it also climbs without limit. Hence nothing possessing mass can be accelerated to the speed of light, though it can come close. On the other hand, a massless particle must move at the speed of light for the medium through which it is moving. This is another implication of the Lorenz equations, though I don’t grasp exactly how it’s required to be the case. It would be theoretically possible to have something that may only move faster than light – the “tachyons” of theoretical physics and SF. However, (1) it would be effectively impossible to detect a tachyon, and (2) if tachyons existed, according to some theorists, they would have effects on what we can observe and detect that are not present. But the effect of the Lorenz equations is such that it would theoretically be possible to send something to the Andromeda Galaxy at relativistic speeds – a 1 gravity acceleration and decleration – in 21 years – _measured by its own internal time_. But the duration of that object’s trip, as measured by someone staying on Earth and observing it, would be on the order of several million years. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 30, 2003, 7:25pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/12 "2003-12-30T19:25:04Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\*Jeez. I forgot Karl. Big Karl Gauss - major contributor just prior to Maxwell on the on the electromagnetism thing, but also the dude who laid the foundation for the whole curved space-time thing that bacame Einstein’s _real_ achievement: general relativity. Special relativity is popularly attributed to Einstein, but it wasn’t really a big deal. Other people had already developed it to the point where it was pretty sure to become mainstream within a couple of years, with or without Einstein. > > Oh yeah the OP. > > 2.99792458x10[sup]8[/sup] ms[sup]-1[/sup] is just a measured value. You wanna postulate 3.13x10[sup]8[/sup]ms[sup]-1[/sup], go right ahead. It’s at odds with measurement, however. > > You wanna argue that it shouldn’t be a limit, take it up with Poincare. \*\* Actually 2.997 924 58 x 10[sup8[/sup] is the exact speed og light by definition. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [December 30, 2003, 7:34pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/13 "2003-12-30T19:34:00Z")
> [@](#): > > \*Originally posted by MC Master of Ceremonies \* > \*\*Actually 2.997 924 58 x 10[sup]8[/sup] is the exact speed og light by definition. \*\* Isn’t that, in effect, a definition of the meter (or the second) rather than of the speed of light? I mean, the speed of light = 1, by definition; it’s up to our technology how closely we can measure it in standardized units… (These arguments can run backwards and forwards… I once noted how impressive it is that we can measure the charge of the electron to 11 decimal places… A friend sneered, “The charge of the electron is exactly 1.” I smiled and said how impressive it is that we can measure coulombs to 11 decimal places.) Trinopus ---
**Author:** ![robo99](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@robo99](https://boards.straightdope.com/u/robo99)\ **Post date:** [December 30, 2003, 7:39pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/14 "2003-12-30T19:39:57Z")
…of course these numbers are for the speed of light _in a vacuum_ - clarification for newbies. ---
**Author:** ![DreadCthulhu](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@DreadCthulhu](https://boards.straightdope.com/u/DreadCthulhu)\ **Post date:** [December 30, 2003, 7:57pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/15 "2003-12-30T19:57:38Z")
Well, there are a couple theoritical ways around the speed of light limit, which involve bending and manipulating space-time itself(space can move faster than light), that are not blatant violations of the laws of physics. The most common theories you might hear about are wormholes & “warp” drives. Of course, these methods would require both really exotic matter and ludicious amounts of energy, meaning it will be a while before we could use them. ---
**Author:** ![Meganeko](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Meganeko](https://boards.straightdope.com/u/Meganeko)\ **Post date:** [December 30, 2003, 8:17pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/16 "2003-12-30T20:17:46Z")
> [@](#): > > \*Originally posted by DreadCthulhu \* > \*\*Well, there are a couple theoritical ways around the speed of light limit, which involve bending and manipulating space-time itself(space can move faster than light), that are not blatant violations of the laws of physics. The most common theories you might hear about are wormholes & “warp” drives. Of course, these methods would require both really exotic matter and ludicious amounts of energy, meaning it will be a while before we could use them. \*\* I’ve heard it said that travelling faster than light, whether by wormholes or warps or whatever, is completely ruled out because it violates causality. Here’s [an explanation](http://www.physicsguy.com/ftl/html/FTL_part4.html#sec:howwegetup) which doesn’t rely on mindboggling mathematics. ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [December 30, 2003, 8:41pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/17 "2003-12-30T20:41:09Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\ ***Shade** , you’re a mathematician, right? Gotta take issue with you on a few things: > > 1. You failed to snicker at my “complex” joke. (In which I really should have said some thing like “Maxwell and Heaviside”, rather than just Maxwell) 😉 > 2. Twasn’t Einstein that derived it. Maxwell, Lorentz and Minkowski had more to do with it. Big Al was a contributor, along with Riemann, Stokes, Hertz, Poincare, _et al_. > 3. It’s not something that can be “proved” in the mathematical sense. 🙂 \*\* OK, OK, I’ll apologize. I did, obviously, snicker at your joke, but assumed you’d know that without my saying so. Substitute “an Einstein” for “Einstein.” I was using proved as in proving from the axioms that the speed of light is the speed limit. However, I did use “your” where I meant “you’re” so shoot me anyway. Sorry. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [December 30, 2003, 9:15pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/18 "2003-12-30T21:15:31Z")
> [@](#): > > \*Originally posted by Trinopus \* > \*\*Isn’t that, in effect, a definition of the meter (or the second) rather than of the speed of light? > > I mean, the speed of light = 1, by definition; it’s up to our technology how closely we can measure it in standardized units… > > (These arguments can run backwards and forwards… I once noted how impressive it is that we can measure the charge of the electron to 11 decimal places… A friend sneered, “The charge of the electron is exactly 1.” I smiled and said how impressive it is that we can measure coulombs to 11 decimal places.) > > Trinopus \*\* The speed of light (in a vacuum in SI units) is now used to define metres (in SI units), so a metre is defined as the length of the path that a ray of light travels in 1/299792458 seconds (seconds are defined by the oscilattions between energy states in IIRC caesium). ---
**Author:** ![DreadCthulhu](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@DreadCthulhu](https://boards.straightdope.com/u/DreadCthulhu)\ **Post date:** [December 30, 2003, 9:20pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/19 "2003-12-30T21:20:36Z")
> [@](#): > > \*Originally posted by Meganeko \* > \*\*I’ve heard it said that travelling faster than light, whether by wormholes or warps or whatever, is completely ruled out because it violates causality. Here’s [an explanation](http://www.physicsguy.com/ftl/html/FTL_part4.html#sec:howwegetup) which doesn’t rely on mindboggling mathematics. \*\* Welcome to the board \*\* Meganeko.\*\* Now it is true that a FTL travel or communications method could/would violate causality, but the real question is - why can’t causality be violated?? 😃 ---
**Author:** ![Meganeko](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Meganeko](https://boards.straightdope.com/u/Meganeko)\ **Post date:** [December 30, 2003, 9:49pm UTC](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742/20 "2003-12-30T21:49:13Z")
> [@](#): > > \*Originally posted by DreadCthulhu \* > **Welcome to the board \*\* Meganeko.** Now it is true that a FTL travel or communications method could/would violate causality, but the real question is - why can’t causality be violated?? 😃 \*\* Oh damn, you’ve got me there. Isn’t a causality violation logically impossible, because cause and effect get mixed up? Like the “travel back in time and shoot your grandpa” thing? Though one of the solutions to that ancient paradox is to invoke branching timelines (shoot your grandpa and you don’t get any paradoxes; you just end up creating a new timeline, where you never get born). I suppose that could get round FTL’s causality violations. [Next page](https://boards.straightdope.com/t/why-is-light-speed-the-limit/221742.md?page=2)