# What would I see if I am in a spaceship going at 99.99% the speed of light? **URL:** \ **Category:** Factual Questions\ **Created:** [December 24, 2010, 7:34pm UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306 "2010-12-24T19:34:36Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![automagic](https://avatars.discourse-cdn.com/v4/letter/a/a698b9/32.png) [@automagic](https://boards.straightdope.com/u/automagic)\ **Post date:** [December 24, 2010, 7:34pm UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/1 "2010-12-24T19:34:36Z")
Here is the scenario. I am in Spaceship A and my friend is in Spaceship B. Each spaceship can accelerate to 99.99% the speed of light in seconds. If Spaceship A and Spaceship B start at the same point and travel in opposite directions what would I see if I looked in Spaceship B’s direction? It seems to me that any light coming from Spaceship B would never reach me and it would quickly disappear regardless of how good my telescope was. Is this accurate? ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [December 24, 2010, 10:47pm UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/2 "2010-12-24T22:47:37Z")
No, light from B will reach you. In your reference frame, the light emitted by B will travel toward you at _c_, but will be immensely red-shifted. In addition, if you could see B, the ship would look foreshortened, events on board would appear to happen very slowly, and the ship would appear to be traveling at some fraction of _c_. Incidentally, A and B are only traveling at 0.9999_c_ relative to the starting point, or any point in the same frame of reference. ---
**Author:** ![Yumblie](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@Yumblie](https://boards.straightdope.com/u/Yumblie)\ **Post date:** [December 25, 2010, 12:58am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/3 "2010-12-25T00:58:54Z")
To expand upon that, using the normal intuitive addition of velocities formula, you in ship A would see ship B go away from you at nearly twice the speed of light. [But addition of velocities formula doesn’t actually work that way.](http://www.straightdope.com/columns/read/418/if-i-fire-a-gun-while-near-light-speed-will-the-bullet-exceed-light-speed) The reason for this is that light breaks all the rules. No matter how fast you’re going with respect to anything else, light will always be traveling at _c_ away from you. So since ship B isn’t actually moving away from you faster than _c_, the light will reach you eventually. ---
**Author:** ![fumster](https://avatars.discourse-cdn.com/v4/letter/f/e9c0ed/32.png) [@fumster](https://boards.straightdope.com/u/fumster)\ **Post date:** [December 25, 2010, 1:00am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/4 "2010-12-25T01:00:15Z")
Isn’t the answer basically that he already is traveling at 99.99% of C relative to something? ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [December 25, 2010, 2:56am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/5 "2010-12-25T02:56:09Z")
If, however, spaceship A is accelerating, then you would not be able to see spaceship B. In fact you would create a causal disconnect behind you (an event horizon) and you’d even get to experience some Hawking radiation. ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [December 25, 2010, 3:16am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/6 "2010-12-25T03:16:11Z")
> [@Ring](#): > > If, however, spaceship A is accelerating, then you would not be able to see spaceship B. In fact you would create a causal disconnect behind you (an event horizon) and you’d even get to experience some Hawking radiation. I’m not sure where you’re getting this from. Accelerating, even when the relative velocity of the two spacecrafts is near c, would produce none of these effects. ---
**Author:** ![The\_Seventh\_Deadly\_Finn](https://avatars.discourse-cdn.com/v4/letter/t/6bbea6/32.png) [@The\_Seventh\_Deadly\_Finn](https://boards.straightdope.com/u/The_Seventh_Deadly_Finn)\ **Post date:** [December 25, 2010, 3:17am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/7 "2010-12-25T03:17:41Z")
> [@Ring](#): > > If, however, spaceship A is accelerating, then you would not be able to see spaceship B. In fact you would create a causal disconnect behind you (an event horizon) and you’d even get to experience some Hawking radiation. Do you have a cite for this, or can you explain in more detail? I’m not disputing it; I just can’t remember this part of the relativistic-effects conversation very well. Mind you, it sounds familiar, but I can’t recall the details. ---
**Author:** ![The\_Seventh\_Deadly\_Finn](https://avatars.discourse-cdn.com/v4/letter/t/6bbea6/32.png) [@The\_Seventh\_Deadly\_Finn](https://boards.straightdope.com/u/The_Seventh_Deadly_Finn)\ **Post date:** [December 25, 2010, 3:18am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/8 "2010-12-25T03:18:46Z")
… ---
**Author:** ![snailboy](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@snailboy](https://boards.straightdope.com/u/snailboy)\ **Post date:** [December 25, 2010, 4:20am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/9 "2010-12-25T04:20:33Z")
If I did the math correctly, their velocity relative to each other would be 0.99994999975c. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [December 25, 2010, 4:29am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/10 "2010-12-25T04:29:57Z")
> [@The\_Hamster\_King](#): > > I’m not sure where you’re getting this from. Accelerating, even when the relative velocity of the two spacecrafts is near c, would produce none of these effects. Maybe before you make a post like that you should check out “Rindler Horizon” and “Unruh effect.” ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [December 25, 2010, 5:33am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/11 "2010-12-25T05:33:46Z")
> [@Ring](#): > > Maybe before you make a post like that you should check out “Rindler Horizon” and “Unruh effect.” Ignorance fought. You are correct. ---
**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:** [December 25, 2010, 6:11am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/12 "2010-12-25T06:11:28Z")
I believe such a large percentage of c would produce the following optical effect: A circle of blue shifted stars…distorted as if photographed through a fish-eye lens…directly in front of you; another circle of red-shifted , equally distorted starlight directly behind; and to the sides…_nothing._ At your speed lateral photons would literally miss your retinas. (half remembered from a 30 year old memory of Carl Sagan’s COSMOS) ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [December 26, 2010, 3:58am UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/13 "2010-12-26T03:58:25Z")
> [@The\_Hamster\_King](#): > > Ignorance fought. You are correct. Sorry about getting a little snippy earlier, I guess I just didn’t expect to be disagreed with. I’ve always thought the Unruh effect is pretty nifty, because it shows the symmetry between gravitation and acceleration. An observer suspended outside the event horizon, with a local g value, will experience the same temperature radiation bath, as an observer accelerating through flat spacetme at that g. ---
**Author:** ![Yumblie](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@Yumblie](https://boards.straightdope.com/u/Yumblie)\ **Post date:** [December 26, 2010, 8:24pm UTC](https://boards.straightdope.com/t/what-would-i-see-if-i-am-in-a-spaceship-going-at-99-99-the-speed-of-light/565306/14 "2010-12-26T20:24:14Z")
> [@Enola\_Straight](#): > > I believe such a large percentage of c would produce the following optical effect: > > A circle of blue shifted stars…distorted as if photographed through a fish-eye lens…directly in front of you; another circle of red-shifted , equally distorted starlight directly behind; and to the sides…_nothing._ At your speed lateral photons would literally miss your retinas. > > (half remembered from a 30 year old memory of Carl Sagan’s COSMOS) [Something like this.](http://www.youtube.com/watch?v=SIfRZhztNos)