# How to have light move faster than C **URL:** \ **Category:** The BBQ Pit\ **Created:** [February 24, 2014, 9:53pm UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160 "2014-02-24T21:53:29Z")\ **Posts on this page:** 20\ **Page:** 16
**Author:** ![Kimble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kimble/32/19185_2.png) [@Kimble](https://boards.straightdope.com/u/Kimble)\ **Post date:** [March 1, 2014, 6:55pm UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/302 "2014-03-01T18:55:24Z")
> [@Smeghead](#): > > The mods have instructed him not to start any more threads on relativity, so you’re going to have to do it here, methinks. I interpreted the mods’ instructions to mean that questioning of relativity itself has to go in Great Debates (in theory) or here (in practice); questions answered by relativity aren’t affected by their instructions. * * * To those who seem to have more of a grasp on the subject than I: Are these statements fair to make? 1. As someone whose native language dialect is US English, I can say “ether” and not “aether” or “æther”. 2. Lorentz’s ether theory _cannot_ be a factor in disproving SR because it makes exactly the same predictions as SR. 3. SR cannot be disproved without showing an example where two observers either: 2a) observe different values of _c_, or 2b) are in different inertial frames of reference and experience different physical laws * * * Edit: Also, thanks to everyone for all the sensible replies in these threads – I’ve learned a ton of stuff, both historical and physical. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [March 1, 2014, 8:08pm UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/303 "2014-03-01T20:08:04Z")
> [@Kimble](#): > > . . . 0) As someone whose native language dialect is US English, I can say “ether” and not “aether” or “æther”. . . . If you Google the two terms, they are both in use. Ether seems to be somewhat more used, in fact. Aether has the advantage of being distinct from the anaesthetic chemical ether. ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 1, 2014, 10:45pm UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/304 "2014-03-01T22:45:24Z")
Hi Pasta I wrote a reply in my normal format, addressing what you said but things became even longer than usual, so I am starting over and will not directly address all things you mentioned or all the thought experiments and arguments I wanted to, but feel free to press me on anything you really wanted answered. I also had an interesting new idea, and while it is new and so I could be mistaken, I think it is simple and impossible enough and breaks SR without trying to imagine contradictions that SR insists we must. The thing about imaging something unimaginable that you must imagine. Is if you try and imagine the experiment you have to go from no relative motion, to relative motion (inconsistent experiences) to no relative motion before SR can no longer claim that 2 twins can’t now be obviously older as they experienced. The point is it becomes as clear as mud and communication between them that should be easy to imagine as they are close become impossible to consider, and the weakness seems to apply to me as I try to explain the thought experiment, But in reality it is SR that can’t explain the contradiction for even a nanosecond if direct communication is allowed as is possible if they are passing by each other (arbitrary distance) and not receding/approaching. But the fact is that SR can’t explain what happens if the accumulated time paradox grows indefinitely while non-simultaneity is small and limited is an absolute failure, and IMO rotation must face time dilation under SR if stationary light clocks seen by the rotating frame are to conform to C, more about that later. Regarding GR’s disproof and SR applying to an accelerating frame… [http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Clock\_Hypothesis](http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html#Clock_Hypothesis) \*The Clock Hypothesis The clock hypothesis states that the tick rate of a clock when measured in an inertial frame depends only upon its velocity relative to that frame, and is independent of its acceleration or higher derivatives. The experiment of Bailey et al. referenced above stored muons in a magnetic storage ring and measured their lifetime. While being stored in the ring they were subject to a proper acceleration of approximately 1018 g (1 g = 9.8 m/s2). The observed agreement between the lifetime of the stored muons with that of muons with the same energy moving inertially confirms the clock hypothesis for accelerations of that magnitude. Sherwin, “Some Recent Experimental Tests of the ‘Clock Paradox’”, Phys. Rev. 129 no. 1 (1960), pg 17. He discusses some Mössbauer experiments that show that the rate of a clock is independent of acceleration (~1016 g) and depends only upon velocity.\* At any rate the new experiment is hopefully clearer, I had glimpses of this thought experiment previously but I couldn’t keep the thought. To be super clear what we mean by light clock here again is the wiki page: > **[Time dilation](https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_due_to_relative_velocity)** > > Time dilation is the difference in elapsed time as measured by two clocks, either due to a relative velocity between them (special relativity) or due to a difference in gravitational potential between their locations (general relativity). When unspecified, "time dilation" usually refers to the effect due to velocity. > After compensating for varying signal delays due to the changing distance between an observer and a moving clock (i.e. Doppler effect), the observer will measure the moving clock as... Under the heading: Simple inference of time dilation due to relative velocity \*\*So imagine the light clock that the relatively moving observer must see as slowed for him if light is seen to be conforming to C by his view (as he sees a longer path). Now let’s repeat the experiment but place a second orthogonal light clock intersecting the first in the 'stationary frame, now this second light clock is seen by the moving observer to be sending light on the axis of his motion. This means that length contraction will cause him to see the light clock as if the mirrors are closer together and hence this light clock must be have a higher frequency from his view if the light in it is seen by him to conform to C! So now he sees that the time rate in the same location in the same frame is simultaneously faster AND slower than his time! This right here is enough of a paradox to end the the post on, other things can be done to drive home the point further, but I don’t see how this (admittedly fresh) paradox can be solved any other way IF light is to be C, and if light is not C then SR’s basis (Axiom)is false and drops dead entirely.\*\* ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 12:09am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/305 "2014-03-02T00:09:57Z")
> [@Pasta](#): > > This is a principle challenge with thought experiments. We have a privileged, omniscient view since we are the thinker of the experiment. However, the characters in the experiment cannot see everything we can. They are limited to what they can physically measure or what information can be transmitted from point A, time A to point B, time B. Since we are dealing with theortical frameworks that muck up the very concepts of space and time and light transport, I would worry that glossing over the exact mechanism of measurement and comparison might be throwing the baby out with the bath water. Do you think this is a valid concern? Could it be that the inconsistent measurements we are hitting are actually because we are viewing the experiment in a way that no real observer could? Perhaps when we think through the nuances of the measurement and the data comparisons, we’ll discover that the mucked up concepts of space and time make things happy again? In my first attempt to reply, I had not even got to this point before I went too long and hard to start again! Firstly I have already argued that the paradox of mutual time dilation must apply to rotation or any slight arc that could describe a portion of a circle of ANY size and that light clocks (oriented normally) must be seen to keep C between different frames. This makes things very different than the normal assertion of the paradox. In the normal form, communication is hampered by non-simultaneity and delay and the fact that the delay is growing (or decreasing). So I grant you that in this instance without a ‘Gods eye view’ or instantaneous communication means, it is only counter-intuitive. But in the short moment the observers pass, OR if the observation time is lengthened as in the time dilation experimentally confirmed to happned in a circular particle accelerator, the 2 frames are in constant sight of each other, obviously they can communicate as they can be physically close and there is a constant delay and negligible and very limited amount of non-simultaneity to worry about where the accumulated time in disagreement increased every moment the experiment continues. So we have a problem, instantaneous communication is essentially an option but we can’t ‘grok’ ‘parse’ ‘imagine’ or get any grip on how that would go. And when they stop (and I have symmetrical arguments if you wish) one or both are going to have their expectation of the advancement of time in the other frame blown! But what could this look like? We can’t just have the disputed time happen as quickly deceleration occurs because light clocks would have to be seen to exceed C. I assert that time dilation without a large distance involved stops being merely counter-intuitive, but is now no longer possible. Another issues with measuring the length contraction of the circumference of a disk. User Ronald RayGun agreed with me that length contraction will occur but that the radius will not change so space becomes warped (no longer Pi). I accepted that, but if a disk is rotated so the cm lengths marked on it can be observed to shrink (via strobe light) then a ruler on the Lab frame could verify this. BUT if this is so then it should be possible to measure around it with a measuring tape (they have no radius as such), and have the measuring tape read a value where the start covers the other numbers, but the rotating frame sees the tape to have become shorter and can’t be fitting around it reading that value. You can also have arguments with counter-rotation if symmetry is desired. ## SR Can’t apply to rotating frames but if it doesn’t it can’t apply to very much real or actual motion at all since perfectly linear motion would be impossibly rare. And it won’t solve problems about conventionally oriented light clocks. More on the light clock that is oriented so length contraction occurs… As possibly an interesting point to show that I am normally able to spot where a thought experiment fails, I might have seen an issue with the (maybe an hour old) orthogonal light clock experiment, the changing position changes the distance light has to go in each direction (shortening and lengthening the path equally) Time is now still seen to be faster and slower at once (potentially) from one view, the light heading in one way has further to go and the other way has less distance. Furthermore since even this light clock now experiences 2 equal and opposite distortions unrelated directly to length contraction, the net difference is that despite the new location relative motion has provided, shrinking has still raised it’s frequency. So this does not bust the argument (phew, I wasn’t sure when I started off), but it should be covered as a factor that only a whole cycle will show a clear net effect of time acceleration without doing the math to know if the frequency raising effect of length contraction will be dominant even when during the longer phase. ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 12:40am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/306 "2014-03-02T00:40:52Z")
I forgot my promise to pasta about 1 on 1 communication, So I am deleting this reply. ---
**Author:** ![Kimble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kimble/32/19185_2.png) [@Kimble](https://boards.straightdope.com/u/Kimble)\ **Post date:** [March 2, 2014, 1:28am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/307 "2014-03-02T01:28:36Z")
> [@mythoughts](#): > > So imagine the light clock that the relatively moving observer must see as slowed for him if light is seen to be conforming to C by his view (as he sees a longer path). > > Now let’s repeat the experiment but place a second orthogonal light clock intersecting the first in the 'stationary frame, now this second light clock is seen by the moving observer to be sending light on the axis of his motion. This means that length contraction will cause him to see the light clock as if the mirrors are closer together and hence this light clock must be have a higher frequency from his view if the light in it is seen by him to conform to C! > > So now he sees that the time rate in the same location in the same frame is simultaneously faster AND slower than his time! > > This right here is enough of a paradox to end the the post on, other things can be done to drive home the point further, but I don’t see how this (admittedly fresh) paradox can be solved any other way IF light is to be C, and if light is not C then SR’s basis (Axiom)is false and drops dead entirely. To make the discussion easier, I’ll name the stationary observer Stacy and the moving observer Moe. Stacy’s female; the differences in gender will make he/she references easier to follow. Moe will be in a rocket ship, as is customary. So, your experiment is saying that Moe has two light clocks in overlapping locations of his ship, like the sides of a square – one with photons bouncing up and down, the other bouncing fore and aft. Assuming that’s correct, let’s move on. Numbers! Moe is moving at 0.8c relative to Stacy. The mirrors are 1 light-microsecond (299.792458 meters) apart. Stacy sees Moe’s ship contracted by relativistic motion such that his fore/aft mirrors are ~180 meters apart. **Moe _does not_ observe contraction of his ship, his clocks, his body, his heartbeat, etc. To him, everything looks and acts like the ship is stationary. The light bounces off his mirrors once per microsecond, which are ~300 m apart.** That is important. 🙂 Stacy sees light bouncing off Moe’s up/down mirror every (5/3) µs. When Stacy sees light bounce off Moe’s aft mirror, it starts moving at 1.0c toward the front of the ship. Keep in mind that the fore mirror appears to Stacy to be ~180 meters away and moving at 0.8c. There’s nothing special about this math; the answer is ~3 µs. Once that light hits the fore mirror, it bounces back at 1.0c heading toward the back of the ship, which is moving to meet it at 0.8c. This takes 1/3 µs. (Note that things don’t appear to happen at the same time for Moe and Stacy. Your reading assignment, should you choose to accept it: [Relativity of simultaneity](http://en.wikipedia.org/wiki/Relativity_of_simultaneity). Conclusion: No paradox. ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [March 2, 2014, 1:36am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/308 "2014-03-02T01:36:36Z")
You’ve exceeded the OP’s math abilities. [“Math class is tough”](http://www.youtube.com/watch?v=NO0cvqT1tAE) ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 1:50am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/309 "2014-03-02T01:50:17Z")
> [@Kimble](#): > > To make the discussion easier, I’ll name the stationary observer Stacy and the moving observer Moe. Stacy’s female; the differences in gender will make he/she references easier to follow. Moe will be in a rocket ship, as is customary. > > Conclusion: No paradox. I doubt I will come to the same conclusion when I check what you say, but I suspect you could be confusing the effects of motion with length contraction. And declaring non-simultaneity from a single view from one frame to one location in another frame to not be contradicting, and I would not agree. However my sister is coming back from being in Canada for 6 years today (no really, unrelated to the meme, but I doubt you know her) so I doubt I will have an answer today (my time), but I will reply to this. But would you agree that if somehow (I am not saying it is possible) the motion was removed from the equation while keeping the length contraction, that clock must be seen to tick faster? (just the length contracted one) And would be assumed to conform to the biological clock known as Moe? (Moe would be seen to age/move faster by Stacy) along with more conventional clocks. ---
**Author:** ![zweisamkeit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zweisamkeit/32/4360_2.png) [@zweisamkeit](https://boards.straightdope.com/u/zweisamkeit)\ **Post date:** [March 2, 2014, 2:06am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/310 "2014-03-02T02:06:58Z")
Thanks, **mythoughts** (and thanks to **Czarcasm** for telling him the post number). I’m glad you had just missed it, which is understandable since there’s a lot going on! I wonder if others would be interested in the course, too; we could even make a discussion thread to discuss the course. ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 2:41am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/311 "2014-03-02T02:41:39Z")
> [@Kimble](#): > > Your reading assignment, should you choose to accept it: [Relativity of simultaneity](http://en.wikipedia.org/wiki/Relativity_of_simultaneity). > > Conclusion: No paradox. One last thought before I tidy the house… Are you saying that Stacy wouldn’t see the clock aligned in the direction of motion to keep faster time than the other 90 degree one? Or are you saying that she would and SR is cool with that? I would assert that neither would be true, the first because obviously it is length contracted and must agree with C from Stacy’s view. The second because it still needs a (light) clock in that frame to tick faster than an identical (light) clock Stacy might have and secondly if Moe had a single LCD display that kept a record of the total ticks on each one they could not agree on how that changes. Even IF SR were cool with it reality wouldn’t be. Sorry, I just need to go over every number you gave to understand which is at the very limit of my math skill (not over) but still now easy. And you are using fractions (yuck) not decimal for microseconds which is another thing I’d have to convert. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [March 2, 2014, 3:52am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/312 "2014-03-02T03:52:28Z")
> [@mythoughts](#): > > . . . I suspect you could be confusing the effects of motion with length contraction. A completely meaningless assertion. > [@](#): > > But would you agree that if somehow (I am not saying it is possible) the motion was removed from the equation while keeping the length contraction, that clock must be seen to tick faster? If motion was removed from the equation, then…the objects wouldn’t be moving. There would be no length contraction nor time dilation. The objects would be in the same frame of reference. > [@mythoughts](#): > > . . . Are you saying that Stacy wouldn’t see the clock aligned in the direction of motion to keep faster time than the other 90 degree one? What “90 degree one?” The orientation of a clock won’t change the rate at which it runs. > [@](#): > > The second because it still needs a (light) clock in that frame to tick faster than an identical (light) clock . . . What is a “(light) clock?” A clock behaves differently than a source of light. Clocks tick faster and slower; light doesn’t. This guy is doing a “word salad” game here. He’s prattling. His muons don’t possess an integral spin. ---
**Author:** ![Kimble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kimble/32/19185_2.png) [@Kimble](https://boards.straightdope.com/u/Kimble)\ **Post date:** [March 2, 2014, 4:00am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/313 "2014-03-02T04:00:14Z")
> [@mythoughts](#): > > I doubt I will come to the same conclusion when I check what you say, but I suspect you could be confusing the effects of motion with length contraction. I’ll wait for a fuller reply to comment on that. > [@](#): > > And declaring non-simultaneity from a single view from one frame to one location in another frame to not be contradicting, and I would not agree. I haven’t done the math, but I don’t think that you can’t keep simultaneity unless light has an infinite speed. But that’s another topic for another day. > [@](#): > > However my sister is coming back from being in Canada for 6 years today (no really, unrelated to the meme, but I doubt you know her) so I doubt I will have an answer today (my time), but I will reply to this. Okay. No problem. > [@](#): > > But would you agree that if somehow (I am not saying it is possible) the motion was removed from the equation while keeping the length contraction, that clock must be seen to tick faster? (just the length contracted one) And would be assumed to conform to the biological clock known as Moe? (Moe would be seen to age/move faster by Stacy) along with more conventional clocks. If you mean “removed from the equation” literally, here’s what Stacy would see: Moe’s fore/aft clock would be faster than it looked to Moe (1.2 µs per complete cycle). Moe’s up/down clock would be the same, 2.0 µs per cycle. Moe’s personal clock would be paradoxical; if forced to assign a number to it, I’d guess it would be 1.13 times faster than Stacy’s. But that’s math with no connection to reality. 🙂 If you mean that more figuratively… I’ll deal with that later. Your questions in your next post will provide more meaningful answers. > [@](#): > > Are you saying that Stacy wouldn’t see the clock aligned in the direction of motion to keep faster time than the other 90 degree one? She would see them keep the same slow time – 3.333 µs/cycle for what Moe would see as 2.0 µs/cycle. The up/down clock would take 1.667 µs to go from one mirror to the other. The fore/aft clock would take 3 µs going forward and 0.333 µs going backward. If Stacy had an identical copy of that set of clocks with her, she would see both parts of the clock at 2 µs/cycle. _And Moe would see both of Stacy’s clocks as slow – 3.333 µs/cycle._ > [@](#): > > I would assert that neither would be true, the first because obviously it is length contracted and must agree with C from Stacy’s view. That statement explains a LOT of where you disagree with everyone else. Short version: Length contraction isn’t everything. You can’t ignore the ship moving away from the light. A long answer will be forthcoming. > [@](#): > > And you are using fractions (yuck) not decimal for microseconds which is another thing I’d have to convert. Here’s post 307 without the fractions. (If it’s not clear, I’m using ~ to indicate “approximately”.) [SPOILER]To make the discussion easier, I’ll name the stationary observer Stacy and the moving observer Moe. Stacy’s female; the differences in gender will make he/she references easier to follow. Moe will be in a rocket ship, as is customary. So, your experiment is saying that Moe has two light clocks in overlapping locations of his ship, like the sides of a square – one with photons bouncing up and down, the other bouncing fore and aft. Assuming that’s correct, let’s move on. Numbers! Moe is moving at 0.8c relative to Stacy. The mirrors are 1 light-microsecond (299.792458 meters) apart. Stacy sees Moe’s ship contracted by relativistic motion such that his fore/aft mirrors are ~180 meters apart. Moe does not observe contraction of his ship, his clocks, his body, his heartbeat, etc. To him, everything looks and acts like the ship is stationary. The light bounces off his mirrors once per microsecond, which are ~300 m apart. That is important. Stacy sees light bouncing off Moe’s up/down mirror every 1.667 µs. When Stacy sees light bounce off Moe’s aft mirror, it starts moving at 1.0c toward the front of the ship. Keep in mind that the fore mirror appears to Stacy to be ~180 meters away and moving at 0.8c. There’s nothing special about this math; the answer is ~3 µs. Once that light hits the fore mirror, it bounces back at 1.0c heading toward the back of the ship, which is moving to meet it at 0.8c. This takes 0.333 µs. (Note that things don’t appear to happen at the same time for Moe and Stacy. Your reading assignment, should you choose to accept it: Relativity of simultaneity. Conclusion: No paradox. [/SPOILER] ---
**Author:** ![Kimble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kimble/32/19185_2.png) [@Kimble](https://boards.straightdope.com/u/Kimble)\ **Post date:** [March 2, 2014, 4:10am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/314 "2014-03-02T04:10:04Z")
> [@Trinopus](#): > > What is a “(light) clock?” A clock behaves differently than a source of light. Clocks tick faster and slower; light doesn’t. [Light clock](http://simple.wikipedia.org/wiki/Light_clock)\* – two mirrors that a pulse of light bounce between – often used in relativity demonstrations > [@](#): > > This guy is doing a “word salad” game here. He’s prattling. His muons don’t possess an integral spin. As of now, I think that he thinks that considering both an object’s motion and its length constriction is “double-counting” and will mess up your numbers. My goal: to show him that it’s not. \*[Obligatory xkcd](http://xkcd.com/1133/) ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 4:27am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/315 "2014-03-02T04:27:26Z")
Sister not here yet, house 99% done (ADD you know)… > [@Trinopus](#): > > A completely meaningless assertion. > If motion was removed from the equation, then…the objects wouldn’t be moving. There would be no length contraction nor time dilation. The objects would be in the same frame of reference. I did not say it had to be possible, I said it did not matter. There are 2 effects going on. Firstly re-imagine the experiment if the speed of light (or whatever is standing in for light) is constant relative to the observer (Stacy), but let us assume we have never heard of length contraction or time dilation as we are discussing this before 1905, and we don’t even agree with Lorentz. So now we have motion without length contraction, as we move relative to the light mirror (the one with the same axis of motion as ours) we see that the light has a different distance to go depending on the direction since we see the speed of light as constant but the mirrors keep moving. I wanted to separate that effect, the effect that length contraction is not responsible for the time we see light moving each way changing, getting longer and shorter. If you continued the longer stroke only you would get the wrong results. And as I said I don’t understand what her objection is as I don’t follow her. I’m just trying to understand what she has said in math (maybe) but is unclear about. > [@](#): > > What “90 degree one?” The orientation of a clock won’t change the rate at which it runs. Well I agree, but as far as I can see SR would say otherwise. I am trying to find out if she would agree with your statement… Or disagree but say it is fine under SR due to (IMO an abuse) of non-simultaneity. > [@](#): > > What is a “(light) clock?” A clock behaves differently than a source of light. Clocks tick faster and slower; light doesn’t. Please see the Wiki page I posted earlier, a light clock is a thought experiment with 1 (more moving together) photons bouncing between 2 parallel mirrors. The motion of the observer relative to the axis of travel of the light in my assertion would depend on it’s axis. And SR asserts that how we move if it is across our axis changes our/its time rate because the light is seen to move further. But check out the wikipage I posted earlier. > [@](#): > > This guy is doing a “word salad” game here. He’s prattling. His muons don’t possess an integral spin. You are unaware on an accepted claim of SR, that’s on you not me. If a length contracted ‘light clock’ does not ‘tick faster’ if your view of it is length contracted which reduces the mirror separation, while you must still find light to be C, then I can’t imagine why. But if you can’t follow then you aren’t trying. ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 4:31am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/316 "2014-03-02T04:31:35Z")
> [@Kimble](#): > > [Light clock](http://simple.wikipedia.org/wiki/Light_clock)\* – two mirrors that a pulse of light bounce between – often used in relativity demonstrations > > As of now, I think that he thinks that considering both an object’s motion and its length constriction is “double-counting” and will mess up your numbers. My goal: to show him that it’s not. > > \*[Obligatory xkcd](http://xkcd.com/1133/) To be clear, I am saying that if you only consider half of the clocks full reflection and back again trip you will get the wrong answer. But I think I get you now… ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 4:50am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/317 "2014-03-02T04:50:52Z")
> [@Kimble](#): > > She would see them keep the same slow time – 3.333 µs/cycle for what Moe would see as 2.0 µs/cycle. The up/down clock would take 1.667 µs to go from one mirror to the other. The fore/aft clock would take 3 µs going forward and 0.333 µs going backward. Ok, that is much clearer. But also entirely incongruous! There are a large number of issues at play, firstly I would argue that even without length contraction the path length/time as Stacy see it for Moe’s clocks would differ. The one going up/down is slowed by a lengthening of it’s path as the light zig-zags. The linear one would have to have a different time since the movement (if length contraction didn’t exist or act as real) would still have to run faster! This is an inescapable conclusion even if you decide that length contraction isn’t real somehow as you appear to claim. The motion along the axis of the light path equally lengthens and shortens the course as you numbers above show! No net change! The up and down like clock more familiar to Relativists Obviously has a longer zig zag path. So they aren’t both going to take 3.333 us/cycle! Unless light speed is inconstant. I additionally reject the concept that length contraction can be real but invalid for use here, but we can ignore that as it is not required for me to make my point. Only one axis gives the light further to travel over a cycle! ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 4:58am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/318 "2014-03-02T04:58:27Z")
> [@mythoughts](#): > > The linear one would have to have a different time since the movement (if length contraction didn’t exist or act as real) would still have to run faster! Once more: The linear one would have to have a different time for a cycle since the movement (if length contraction didn’t exist or act as real) would not effect the distance light moves over a full cycle and hence still have to run faster! (by comparison). ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 5:11am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/319 "2014-03-02T05:11:45Z")
> [@mythoughts](#): > > And as I said I don’t understand what her objection is as I don’t follow her. > I’m just trying to understand what she has said in math (maybe) but is unclear about. > I am trying to find out if she would agree with your statement… BTW I just realized Kimble is not necessarily equivalent/similar to Kimberly, and hence may be a guy. If so, sorry. ---
**Author:** ![Trinopus](https://avatars.discourse-cdn.com/v4/letter/t/2bfe46/32.png) [@Trinopus](https://boards.straightdope.com/u/Trinopus)\ **Post date:** [March 2, 2014, 5:33am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/320 "2014-03-02T05:33:15Z")
> [@Kimble](#): > > [Light clock](http://simple.wikipedia.org/wiki/Light_clock)\* – two mirrors that a pulse of light bounce between – often used in relativity demonstrations . . . Cool! Thank you. I was wrong in condemning **mythoughts** for using the term. I apologize. ---
**Author:** ![mythoughts](https://avatars.discourse-cdn.com/v4/letter/m/7993a0/32.png) [@mythoughts](https://boards.straightdope.com/u/mythoughts)\ **Post date:** [March 2, 2014, 5:50am UTC](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160/321 "2014-03-02T05:50:35Z")
> [@Trinopus](#): > > Cool! Thank you. I was wrong in condemning **mythoughts** for using the term. I apologize. I very much appreciate that! Let’s keep things on a basis of respecting others even if their beliefs differ. That was big of you. And you just did something that I have seen no one else do, both admit you were wrong and rescind an insult! If I am wrong, personal attacks should not be needed to show it. [Previous page](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160.md?page=15) [Next page](https://boards.straightdope.com/t/how-to-have-light-move-faster-than-c/682160.md?page=17)