# If you are traveling at the speed of light in a dark tunnel... **URL:** \ **Category:** Factual Questions\ **Created:** [March 20, 2004, 1:20am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324 "2004-03-20T01:20:17Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Campione](https://avatars.discourse-cdn.com/v4/letter/c/7feea3/32.png) [@Campione](https://boards.straightdope.com/u/Campione)\ **Post date:** [March 20, 2004, 1:20am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/1 "2004-03-20T01:20:17Z")
and you’re wearing one of those helmets with a flash light on it, and you flicked it on, what happens? Sorry for the dumbass question. I heard someone ask this before and I can’t remember who. ---
**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:** [March 20, 2004, 1:26am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/2 "2004-03-20T01:26:57Z")
You can’t travel at the speed of light, even theoretically, so the question does not have an answer. ---
**Author:** ![Joe\_Random](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)\ **Post date:** [March 20, 2004, 1:27am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/3 "2004-03-20T01:27:45Z")
> [@Campione](#): > > If you are traveling at the speed of light in a dark tunnel… > > and you’re wearing one of those helmets with a flash light on it, and you flicked it on, what happens? Unfortunately, that’s an invalid question (much like “If you went north from the north pole, where would you be?”) You _can’t_ travel the speed of light, so the question can’t be answered. Now, if you were traveling _close_ to the speed of light (relative to some frame of reference), then the light from the flashlight would appear to travel at the speed of light both to you _and_ to whatever you’re traveling relative to. ---
**Author:** ![DarrenS](https://avatars.discourse-cdn.com/v4/letter/d/977dab/32.png) [@DarrenS](https://boards.straightdope.com/u/DarrenS)\ **Post date:** [March 20, 2004, 1:37am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/4 "2004-03-20T01:37:15Z")
[If you turn on your headlights while driving at the speed of light, what happens?](http://www.straightdope.com/classics/a3_143.html) ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [March 20, 2004, 1:40am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/5 "2004-03-20T01:40:56Z")
[Here](http://www.usatoday.com/news/science/wonderquest/2001-06-06-light-speed.htm) is a good explanation. ---
**Author:** ![trudi\_fermelli](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@trudi\_fermelli](https://boards.straightdope.com/u/trudi_fermelli)\ **Post date:** [March 20, 2004, 1:42am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/6 "2004-03-20T01:42:16Z")
If you travel at the speed of light you are light, so you couldnt be wearing a helmet. In fact you couldnt be in a dark tunnel either. :rolleyes: ---
**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:** [March 20, 2004, 1:50am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/7 "2004-03-20T01:50:52Z")
> [@trudi fermelli](#): > > If you travel at the speed of light you are light, so you couldnt be wearing a helmet. In fact you couldnt be in a dark tunnel either. :rolleyes: well not necessarily other massless particles travel at c. It’s impossible to have refrence frame (in special relativity) for any particle that travels at c with respect to a valid (and therfore all valid) reference frame(s). ---
**Author:** ![trudi\_fermelli](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@trudi\_fermelli](https://boards.straightdope.com/u/trudi_fermelli)\ **Post date:** [March 20, 2004, 2:04am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/8 "2004-03-20T02:04:41Z")
> [@MC Master of Ceremonies](#): > > well not necessarily other massless particles travel at c. It’s impossible to have refrence frame (in special relativity) for any particle that travels at c with respect to a valid (and therfore all valid) reference frame(s). ummmm…yeah, what he said ☹ ---
**Author:** ![trudi\_fermelli](https://avatars.discourse-cdn.com/v4/letter/t/839c29/32.png) [@trudi\_fermelli](https://boards.straightdope.com/u/trudi_fermelli)\ **Post date:** [March 20, 2004, 2:09am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/9 "2004-03-20T02:09:16Z")
Go to the light! Go to the light! 😃 ---
**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:** [March 20, 2004, 2:50am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/10 "2004-03-20T02:50:22Z")
Just to put the icing on this cake, you can’t even ask as a thought experiment what would happen if a massless particle were to try this. Particles that move at the speed of light do not experience time: time stops for them. It’s meaningless to try to speak of doing an action at the speed of light. In its own frame of reference, a massless particle is created moving at the speed of light and with no interval interacts with another particle ending its existence. Darn that Einstein. ---
**Author:** ![Bret](https://avatars.discourse-cdn.com/v4/letter/b/8baadc/32.png) [@Bret](https://boards.straightdope.com/u/Bret)\ **Post date:** [March 20, 2004, 3:14am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/11 "2004-03-20T03:14:08Z")
…but on a different note…Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object? ---
**Author:** ![LtningBug](https://avatars.discourse-cdn.com/v4/letter/l/73ab20/32.png) [@LtningBug](https://boards.straightdope.com/u/LtningBug)\ **Post date:** [March 20, 2004, 8:01am UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/12 "2004-03-20T08:01:58Z")
> [@Bret](#): > > …but on a different note…Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object? This depends on what you mean by taking a picture of a laser beam. It would be entirely possible to fire a laser at a target, and from the side take a picture such that the light being reflected from the laser beam off of particles in the beam’s path would make it appear that the laser beam has been caught in midstride, so to speak. This would require either a very short shutter speed or a very long laser beam path (with the camera appropriately far away). Of course, the above assumes the laser beam is actually hitting many objects (dust, smoke, whatever), and so perhaps is not an answer to your question. I suppose a better answer might be that in order to take a picture of a light beam, the light beam has to hit the camera. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [March 20, 2004, 1:30pm UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/13 "2004-03-20T13:30:50Z")
That would be one HECK of a shutter. Using Google, I find out that (runs to check) light (in a vacuum) could go around _the entire earth_ in .1339 seconds. So, either speed that shutter up a bit, or get Tim Taylor to step up the power on the laser and step waaaaaaaaaayyyy back. ---
**Author:** ![Arturius](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@Arturius](https://boards.straightdope.com/u/Arturius)\ **Post date:** [March 20, 2004, 2:03pm UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/14 "2004-03-20T14:03:52Z")
> [@Exapno Mapcase](#): > > Darn that Einstein. Yeah, he made science no fun ☹ ---
**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:** [March 20, 2004, 10:46pm UTC](https://boards.straightdope.com/t/if-you-are-traveling-at-the-speed-of-light-in-a-dark-tunnel/235324/15 "2004-03-20T22:46:45Z")
> [@Bret](#): > > …but on a different note…Will it ever be possible to take a picture fast enough to capture light (maybe a laser beam) in mid air before it strikes an object? If the beam is sufficiently bright and is travelling trough a medium that scatters light, and you’re viewing from sufficiently far away, then you might even be able to _see_ the progres of the wavefront visually. This has been done with powerful telescopes (not with lasers though) - light from a supernova event (or other sufficiently bright pulse) can be seen to progress through nearby (in astronomical terms) nebulae. This is particularly useful in calculating the distance of the object - knowing that it took a whole year for light to move from distant point A to distant point B, the calculation of distance from the subtended angle is a primary school task.