# Speed of light **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [June 28, 2006, 12:29pm UTC](https://boards.straightdope.com/t/speed-of-light/362474 "2006-06-28T12:29:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MurDuck](https://avatars.discourse-cdn.com/v4/letter/m/3ec8ea/32.png) [@MurDuck](https://boards.straightdope.com/u/MurDuck)\ **Post date:** [June 28, 2006, 12:29pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/1 "2006-06-28T12:29:15Z")
Unca Cease: I used to believe – as you evidently do – that NOTHING could exceed the speed of light. But then a few months ago I read an article in Discover Magazine about the “Big Bang”. According to this article, immediately after the Big Bang, all of the matter created flew outwards at MANY times the speed of light ! I was stunned when I read this. Can anyone contradict this assertion? MurDuck ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [June 28, 2006, 2:22pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/2 "2006-06-28T14:22:29Z")
c…the speed of light …is the speed limit of the universe; it is the fastest velocity known massless particles can transverse a set piece of space over a set piece of time. However, there is no limit as to the speed spacetime itself can stretch. ---
**Author:** ![Zippo342](https://avatars.discourse-cdn.com/v4/letter/z/f07891/32.png) [@Zippo342](https://boards.straightdope.com/u/Zippo342)\ **Post date:** [June 28, 2006, 3:27pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/3 "2006-06-28T15:27:50Z")
> [@Enola Straight](#): > > c…the speed of light …is the speed limit of the universe; it is the fastest velocity known massless particles can transverse a set piece of space over a set piece of time. > > However, there is no limit as to the speed spacetime itself can stretch. I used to believe this, and actually understood what Einstein said with his theory of relativity, however, I remember reading something somewhere about some scientists actually getting light to move faster than the speed of light a few month ago. I’ll try to find it and post a link for you. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [June 28, 2006, 4:16pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/4 "2006-06-28T16:16:16Z")
Welcome to the SDMB, MurDuck. Is this thread in response to one of Cecil’s columns? He has written at least a few on the speed of light, but it would be helpful to know which one you’re referring to. Perhaps this one? [If you were radioactive, would you glow?](http://www.straightdope.com/classics/a990430a.html) ---
**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:** [June 28, 2006, 5:00pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/5 "2006-06-28T17:00:45Z")
[Staff Report, not Cecil](http://www.straightdope.com/mailbag/mphasevel.html) The speed of the Universe’s expansion isn’t even a speed, it’s a frequency. Hence, it can’t actually be compared to the speed of light at all. And there have been many experiments which the popular press has purported to demonstrate something moving faster than light. Some of them are exaggerated or over-hyped, some of them are misinterpreted, some are sloppy measurements, and some are outright lies. None of them is what it purports to be. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [June 28, 2006, 5:17pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/6 "2006-06-28T17:17:13Z")
[tangental] I can barely recall how it went, but there was supposed to be some particle or whatever where it had a twin particle and if you did something to one, its twin would instantaneously do the same thing even though you hadn’t touched it. “They” were saying that this was mostly impressive as it really was instantaneous and thus, faster than light. ? [/tangental] ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [June 28, 2006, 6:25pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/7 "2006-06-28T18:25:18Z")
> [@](#): > > I can barely recall how it went, but there was supposed to be some particle or whatever where it had a twin particle and if you did something to one, its twin would instantaneously do the same thing even though you hadn’t touched it. Unfortunately, it’s not a question of “if you do something”, but of “if something spontanesouly happens”. If you _do_ something, it spoils the experiment. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [June 28, 2006, 9:52pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/8 "2006-06-28T21:52:21Z")
> [@Sage Rat](#): > > [tangental] > > I can barely recall how it went, but there was supposed to be some particle or whatever where it had a twin particle and if you did something to one, its twin would instantaneously do the same thing even though you hadn’t touched it. > > “They” were saying that this was mostly impressive as it really was instantaneous and thus, faster than light. > > ? > > [/tangental] Look up “action at a distance.” From [Wikipedia](http://en.wikipedia.org/wiki/Action_at_a_distance_(physics)) > [@](#): > > Current physical theories incorporate the upper limit on propagation of interaction as one of their basic building blocks, hence ruling out instantaneous action-at-a-distance. While a naïve interpretation of quantum mechanics appears to imply the ability to send signals faster than the speed of light, careful reasoning about these cases shows that no physical signals are actually being sent. Einstein coined the term “spooky action at a distance” to describe these situations, which exhibit quantum entanglement. Relativistic quantum field theory requires interactions to propagate at less than the speed of light, so quantum entanglement cannot be used for faster-than-light-speed propagation of matter, energy, or information. However, it must be understood that a change to one entangled particle does indeed affect the other instantaneously, but this is only known after the experiment is performed and notes are compared, therefore there is no way to actually send information faster than the speed of light. Einstein could not believe this, and therefore he proposed, along with Boris Podolsky and Nathan Rosen, a thought experiment called the EPR paradox. John Bell’s famous experiments addressed the ideas raised in that paper and showed strong evidence for nonlocality and showed that no hidden variables were involved. ---
**Author:** ![pistachio](https://avatars.discourse-cdn.com/v4/letter/p/bbe5ce/32.png) [@pistachio](https://boards.straightdope.com/u/pistachio)\ **Post date:** [July 1, 2006, 4:51am UTC](https://boards.straightdope.com/t/speed-of-light/362474/9 "2006-07-01T04:51:15Z")
I’ve got a bit of a problem with my understanding of the consequences of relativity. Take for example the “pole and barn paradox” illustrating length contraction and time dilation. A man with a 20-foot pole runs at a 10-foot long barn at 0.8c. Due to length contraction in his pov, the barn appears to be 5-feet long, but to the stationary farmer, the pole is 10-feet long and would fit inside his barn with both the front and back doors closed. The analogy goes on to show that to the farmer the back door is only opened once the front door closes, but to the runner the back door opens first. Here’s my question. What might happen if the back door stayed closed (assuming the wall is infinitely hard)? Now the runner’s frame has changed to match the farmer’s, but the reality of the situation is different for each. The farmer has closed the door, but the runner has 10-feet of pole left outside. Am I missing something? 😕 ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [July 1, 2006, 11:40am UTC](https://boards.straightdope.com/t/speed-of-light/362474/10 "2006-07-01T11:40:15Z")
I thought the theory went that massless particals could not not travel anything but the speed of light (intentional double negative). While particals with rest mass could not travel the speed of light. Which does allow for faster then light particals, but they are ‘stuck’ there as they can’t travel the SoL so they can’t get to lower speeds, as the lower speed particals can’t pass that barrior. Though a faster then light partical has not been seen (AFAIK) it has been mathmatically theorized, I think a tachion is one such partical. ---
**Author:** ![John\_W.Kennedy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_w.kennedy/32/1031_2.png) [@John\_W.Kennedy](https://boards.straightdope.com/u/John_W.Kennedy)\ **Post date:** [July 1, 2006, 2:31pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/11 "2006-07-01T14:31:53Z")
A tachyon is a particle that is faster than light by definition. (That is, all particles faster than light are tachyons.) If tachyons exist, they have imaginary rest mass. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [July 2, 2006, 6:10am UTC](https://boards.straightdope.com/t/speed-of-light/362474/12 "2006-07-02T06:10:54Z")
> [@kanicbird](#): > > Though a faster then light partical has not been seen (AFAIK) it has been mathmatically theorized, I think a tachion is one such partical. > [@John W. Kennedy](#): > > A tachyon is a particle that is faster than light by definition. (That is, all particles faster than light are tachyons.) > > If tachyons exist, they have imaginary rest mass. To be a bit more explicit, physicists haven’t really gone looking for theories with tachyons. If a theory happens to predict the existence of a particle that moves faster than light, that particle is referred to as a tachyon. ---
**Author:** ![Random5](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@Random5](https://boards.straightdope.com/u/Random5)\ **Post date:** [July 2, 2006, 5:23pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/13 "2006-07-02T17:23:14Z")
> [@MurDuck](#): > > Unca Cease: > I used to believe – as you evidently do – that NOTHING could exceed the > speed of light. But then a few months ago I read an article in Discover Magazine > about the “Big Bang”. According to this article, immediately after the Big Bang, all of the matter created flew outwards at MANY times the speed of light ! I was stunned when I read this. Can anyone contradict this assertion? > MurDuck When the big bang happend, all kinds of screwed up things happened, at least according to some interpretations. Of course, all of these are just theories and can’t be proven or shown through experiments for the most part, but anyway, some of these theories include. Several other dimensions in addition to our current four (length, width, depth, time) Changes in the strength of the four primary forces (strong nuclear, electromagnetic, weak nuclear, gravity in order of significance now, this order was supposedly different at several points throughout the big bang) I think a little thing like moving faster than the speed of light is hardly an outrageous claim during the big bang. ---
**Author:** ![scott62](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@scott62](https://boards.straightdope.com/u/scott62)\ **Post date:** [July 2, 2006, 6:49pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/14 "2006-07-02T18:49:41Z")
> [@Sage Rat](#): > > [tangental] > > I can barely recall how it went, but there was supposed to be some particle or whatever where it had a twin particle and if you did something to one, its twin would instantaneously do the same thing even though you hadn’t touched it. > > “They” were saying that this was mostly impressive as it really was instantaneous and thus, faster than light. > > ? > > [/tangental] Bill Bryson mentioned it in his “A Short History of Nearly Everything”. Can’t remember in which context but it was something to do with quantum physics. Fascinating. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [July 2, 2006, 6:49pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/15 "2006-07-02T18:49:49Z")
> [@Random5](#): > > Several other dimensions in addition to our current four (length, width, depth, time) This is a string theory (actually, Kaluza-Klein) thing, not a cosmology thing. It has nothing to do with the Big Bang model. > [@](#): > > Changes in the strength of the four primary forces (strong nuclear, electromagnetic, weak nuclear, gravity in order of significance now, this order was supposedly different at several points throughout the big bang) Again, more quantum field theory, and they change even now depending on the energy scale of an interaction (according to the theories). The difference is that in the early times the energy density was a _lot_ higher, so more high-energy interactions took place. > [@](#): > > I think a little thing like moving faster than the speed of light is hardly an outrageous claim during the big bang. Actually it is. Even then, nothing moved _through_ space faster than c. Space _tself_ expanded faster than c, but that’s not a violation of (local) causality. ---
**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 3, 2006, 2:06am UTC](https://boards.straightdope.com/t/speed-of-light/362474/16 "2006-07-03T02:06:58Z")
> [@](#): > > Now the runner’s frame has changed to match the farmer’s, but the reality of the situation is different for each. The farmer has closed the door, but the runner has 10-feet of pole left outside. Am I missing something? If the farmer is running into the barn, and the back door is closed, eventually, that pole is going to hit the back door. At that point, the problem changes in some way: The pole breaks, or the door breaks, or something. At some point, also, the back of the pole will pass the front door of the barn. The question then becomes, does the back of the pole passing the front door happen before something breaks, or after? The farmer and the farmhand at rest in the barn disagree on which happens first, but it doesn’t matter: Either way, the result is a broken pole inside a closed barn. > [@](#): > > This [extra dimensions] is a string theory (actually, Kaluza-Klein) thing, not a cosmology thing. It has nothing to do with the Big Bang model. But of course, such theories have been applied to the early Universe, and incorporated into the Big Bang model. For instance, some models hold that all of the dimensions were originally large, but that during inflation, some shrank exponentially, while others (our familiar four) expanded exponentially. If this is the case, then an understanding of cosmology is key to understanding why we have the particular (apparent) dimensions we do. ---
**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:** [July 3, 2006, 3:22am UTC](https://boards.straightdope.com/t/speed-of-light/362474/17 "2006-07-03T03:22:03Z")
> [@Chronos](#): > > The speed of the Universe’s expansion isn’t even a speed, it’s a frequency. I am so confused. How is it a frequency? And why is it not a speed? If the distance between Point A and Point B grows by 186,000 miles within a 1 second interval, aren’t those points flying apart at the speed of light? (And what the heck does 1 second mean anyway in this context? I-yi-yi). ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [July 3, 2006, 6:22am UTC](https://boards.straightdope.com/t/speed-of-light/362474/18 "2006-07-03T06:22:16Z")
> [@Measure for Measure](#): > > I am so confused. How is it a frequency? > > And why is it not a speed? If the distance between Point A and Point B grows by 186,000 miles within a 1 second interval, aren’t those points flying apart at the speed of light? (And what the heck does 1 second mean anyway in this context? I-yi-yi). Well, that’s just it. In relativity, a “second” is just a unit of distance equal to about 300,000,000 meters. Velocities are measured in “dimensionless” units. Think of it this way: c is just a conversion factor we can set equal to 1, like 3 feet/yard = 1. So a speed of 10 meters/second is the same as 10 m/s = 10 m/s \* 1 = 10 m/s \* (1/300,000,000 s/m) = 1/30,000,000 Where I’ve substituted 1/c (in seconds per meter) in on the third line. I’m not sure about the details (haven’t really dug into inflationary cosmology), but to say the rate of expansion is a frequency means that the units work out to m[sup]-1[/sup], which is the same (up to a conversion factor) as units of s[sup]-1[/sup], which is the same as Hz (“cycles” are dimensionless, so cycles per second is s[sup]-1[/sup]). ---
**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 3, 2006, 5:59pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/19 "2006-07-03T17:59:55Z")
> [@](#): > > I am so confused. How is it a frequency? To expand on **Mathochist** ’s answer, more distant parts of the Universe expand away more quickly. This is a necessary consequence of the homogeneity (uniformity) of the Universe, and applies equally well during the early inflationary stage (when the expansion was ludicrously fast) and today. So you can’t just assign a speed to the Universe’s expansion, because you’d have to specify which part of the Universe is expanding away at that speed. So what you specify instead is the speed per distance: Something twice as far away will be expanding away twice as fast, but it’ll have the same ratio of speed/distance. But a speed is a distance per time, so speed per distance works out to just “per time”, or a frequency. You don’t even have to use dimensionless units for speed (as **Mathochist** suggested) for this to work out. ---
**Author:** ![Caving311](https://avatars.discourse-cdn.com/v4/letter/c/e56c9b/32.png) [@Caving311](https://boards.straightdope.com/u/Caving311)\ **Post date:** [July 7, 2006, 10:52pm UTC](https://boards.straightdope.com/t/speed-of-light/362474/20 "2006-07-07T22:52:28Z")
Okay, first off, we have slowed down the speed of light, even stopped it. Now we’ve apperently made it run faster, backwards, than it does forward. Here’s the link [Scientists Mess with the Speed of Light | Live Science](http://www.livescience.com/technology/050819_fastlight.html) Secondly, our 4 dimensions “length, width, depth, time” only exist because that’s the only way we can percieve things. Thirdly, if I’ve learned anything in my 23 years of life, it’s that ANYTHING is possible if you try hard enough. Seriously, never underestimate the power of the human mind to find a new and faster way of blowing stuff up. I believe there was actually a time when people said “Going faster than the speed of SOUND would liquify one’s body.” It may have been around the time of the whole “flat earth” thing or possibly the “Earth is the center of the universe” thing. But it was believed by the scientists at the time. So, in conclusion, just because we can’t do it now, doesn’t mean we won’t find a way to do it. [Next page](https://boards.straightdope.com/t/speed-of-light/362474.md?page=2)