# How did Einstein prove nothing's faster than light? **URL:** \ **Category:** Factual Questions\ **Created:** [July 21, 2000, 1:50pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343 "2000-07-21T13:50:34Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![RickG](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rickg/32/5174_2.png) [@RickG](https://boards.straightdope.com/u/RickG)\ **Post date:** [July 21, 2000, 6:04pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/21 "2000-07-21T18:04:16Z")
> [@](#): > > \*Originally posted by DrMatrix \* > \*\*I can see how “The speed of light the maximum possible speed” implies “The speed of light is the same for all observers”. I don’t see how the second statement implies the first. The second does imply that nothing can accelerate past the speed of light, but I fail to see how it implies nothing can go faster than light. > > I’m not saying the two statements are not equivalent. I just don’t see it.\*\* It’s all about causality. If the speed of light is the same for all observers, _and_ it is possible to transmit information (information is what may not go FTL), then there exists an inertial frame in which some information is received before it is transmitted. If we believe in causality (i.e. that observations must _follow_ in time the events that are being observed), then one of the antecedents in the if-then statement above must be false. Since we have observed, to incredible precision, that light does indeed have the same speed for all observers, then it must be that nothing _can_ go faster than light. Or strict causality may not be true, in which case all bets are off (since we could build a time machine and break the bank at every gambling establishment in the world :)). Like it or not, it appears that our space-time is just built this way. Apparently, God must be a very good mathematician to have made this all work out so neatly :). Rick ---
**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:** [July 22, 2000, 2:44am UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/22 "2000-07-22T02:44:42Z")
Wow, a lot of these threads lately… Makes me feel right at home 🙂 Wouldn’t you know it, too, I’m exactly three posts too late to add anything to the discussion: DrMatrix mentioned the restriction on accellerating past c, and RickG mentioned the causality problems. Mind you, some of us don’t really see why unidirectional causality is so necessary, but that’s getting into philosophy, there. Oh, and just so I don’t waste this post, tachyons would have to have an imaginary rest mass, not a negative, in order for their relativistic mass to work out to be real. For some reason, nobody seems to want imaginary masses… ---
**Author:** ![cmkeller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmkeller/32/118_2.png) [@cmkeller](https://boards.straightdope.com/u/cmkeller)\ **Post date:** [July 24, 2000, 1:27pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/23 "2000-07-24T13:27:54Z")
Chronos: > [@](#): > > For some reason, nobody seems to want imaginary masses… And certainly not the Pope. 😃 Thanks for the replies, guys. Chaim Mattis Keller ---
**Author:** ![PaulT](https://avatars.discourse-cdn.com/v4/letter/p/b9bd4f/32.png) [@PaulT](https://boards.straightdope.com/u/PaulT)\ **Post date:** [July 24, 2000, 6:46pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/24 "2000-07-24T18:46:24Z")
All of you who are so anxious to postulate tachyons should remember why they are not believed to exist: anything travelling faster than light (in any medium) emits Cerenkov radiation, a sort of sonic boom of light waves. Tachyons, in addition to expending much of their own mass/energy creating that Cerenkov radiation, would also be easily detectable because of it. Until that radiation is detected, it’s safe to say tachyons don’t exist. ---
**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:** [July 25, 2000, 4:15am UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/25 "2000-07-25T04:15:52Z")
Very true, PaulT, except that Cherenkov radiation requires that the particle be able to interact easily with some portion of its surroundings, most typically via an electric charge. All that the nondetection of tachyonic Cherenkov radiation prooves is that tachyons, if they exist, are very weakly interacting. If they were as elusive as, say, axions (a theoretical particle not yet observered) are believed to be, then there’d be no problem with us having not yet detected them. That said, though, they’re still considered pretty durn unlikely. ---
**Author:** ![jb\_farley](https://avatars.discourse-cdn.com/v4/letter/j/9d8465/32.png) [@jb\_farley](https://boards.straightdope.com/u/jb_farley)\ **Post date:** [July 25, 2000, 12:01pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/26 "2000-07-25T12:01:41Z")
also, PaulT, when a tachyon loses energy, it goes faster. it’s the exact opposite of matter; the more energy you add, the slower it goes, but it can never get as slow as c. so if they did expend their energy bustin out action cherenkov style, the would go faster, hence spouting out more c-type radiation. if tachyons were not weakly interacting, they would quickly blow the universe up in a rather graceless way. but that’s assuming that they exist. ---
**Author:** ![The\_Ryan](https://avatars.discourse-cdn.com/v4/letter/t/7feea3/32.png) [@The\_Ryan](https://boards.straightdope.com/u/The_Ryan)\ **Post date:** [July 25, 2000, 7:56pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/27 "2000-07-25T19:56:54Z")
> [@](#): > > \*Originally posted by PaulT \* > \*\*All of you who are so anxious to postulate tachyons should remember why they are not believed to exist: anything travelling faster than light (in any medium) emits Cerenkov radiation, a sort of sonic boom of light waves. \*\* No, all _accelerating particles_ emit radiation. If the paricle travels faster than the radiation, then the radiation is called “Cerenkov” radiation. Note that what one calls a type of radiation does not affect the amount of energy it carries. ---
**Author:** ![PaulT](https://avatars.discourse-cdn.com/v4/letter/p/b9bd4f/32.png) [@PaulT](https://boards.straightdope.com/u/PaulT)\ **Post date:** [July 25, 2000, 8:28pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/28 "2000-07-25T20:28:05Z")
Okay – so tachyons don’t exist UNLESS they are not subject to accelerations – i.e. massless, chargeless bosons. And last time I checked, the standard model predicted only one massless gauge boson – the good old photon, which is NOT tachyonic. Besides, if tachyons can’t be accelerated, then they arent being acted on by forces, and are not only useless, but undetectable – and possibly unfalsifiable. ---
**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:** [July 25, 2000, 9:41pm UTC](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343/29 "2000-07-25T21:41:40Z")
> [@](#): > > And last time I checked, the standard model predicted only one massless gauge boson – the good old photon, which is NOT tachyonic. It also leaves the door open for other massless gauge bosons, such as the graviton. However, all of these particles travel exactly at the speed of light, not faster. As you said, tachyons are probably unfalsifiable, and so far as I know, they’re not really required for any theories relevant to observable particles, either. The only useful purpose I know of for them, is they give the crew of the Enterprise something else to talk about. [Previous page](https://boards.straightdope.com/t/how-did-einstein-prove-nothings-faster-than-light/26343.md?page=1)