# Camera near the speed of light

1. Aug 21, 2011

### Voltaire6022

If you were infinitely close to the speed of light, and you attempted to take a picture of yourself, would it work? Would there be any way to make it work using relative velocities?

2. Aug 21, 2011

### Pengwuino

What? Structure the question better.

3. Aug 21, 2011

### Voltaire6022

Say two people are on a spaceship travelling at near speed of light. If one wants to take a picture of the other, would that be possible?

EDIT: The picture would be taken by the person in the rear of the craft, facing the front.

4. Aug 21, 2011

### elfmotat

They shouldn't see nor feel anything strange, assuming they are moving with constant, uniform velocity (with respect to some other observer, of course - in their frame they are stationary). So yes, they will be able to take a picture.

5. Aug 21, 2011

### Pengwuino

Yes, if they are both on the same spaceship traveling at near the speed of light, they would be able to take pictures easily. They wouldn't even notice anything strange because relative to each other, both of them are at rest.

The spaceship traveling near the speed of light must be traveling at that speed relative to something else, and it certainly isn't traveling at that speed relative to the people inside of it. You would have to say the spaceship is traveling near the speed of light relative to say, a passing planet or star or whatever. And even then, on board, nothing peculiar will happen.

The interesting question, on the other hand, would be if someone on a passing planet tried to take a picture of someone on the spaceship, then you'd see relativistic effects!

Last edited: Aug 21, 2011
6. Aug 21, 2011

### Voltaire6022

Much less exciting than what I was hoping, but thanks :P

7. Aug 23, 2011

### nitsuj

That's not an interesting question, especialy not the interesting question.

Yea I bet that photo would turn out real well. :uhh:

At speeds "infinitely" close to c, the answer they "wouldn't notice anything different and could take pictures easily" is moot.

8. Aug 23, 2011

### HallsofIvy

That is, after all, the whole point of "relativity". The two people are, relative to each other, stationary.

9. Aug 23, 2011

### elfmotat

What? You don't think that a photo showing relativistic effects would be interesting?

That doesn't really make any sense. That IS the answer - how can it be "moot?"

10. Aug 23, 2011

### nitsuj

Never said I don't think that a photo showing relativistic effects would be interesting.

I said that it is not an interesting question, let alone, the interesting question.

it is not possible so that makes it moot.

11. Aug 23, 2011

### elfmotat

In principle it is possible, so the question is not moot.

12. Aug 23, 2011

### Pengwuino

Why is it not possible? In a sense that's what astronomy is all about... although maybe the things they see are more often GR effects than SR ones

13. Aug 23, 2011

### pervect

Staff Emeritus
I think there may be a semantic issue here. If you had a photo that showed effects depending on "velocity through space" or "absolute velocity", they wouldn't be relativistic effects. They'd be evidence that relativity was wrong.

Note that we (or at least I) don't want to start a debate on "is relativity right or wrong" here. The experimental evidence is out there for those who want to study it (such as the failure of previous attempts to measure the absolute velocity of the Earth through space through the M.M. experiment, for starters).

The forum is mostly dedicated to helping people who want to understand relativity to understand it. And part of understanding relativity is understanding that things don't look any different depending on your velocity, this is one of the fundamental principles.

14. Aug 23, 2011

### elfmotat

I think you may have misunderstood what nitsuj was saying. He wasn't arguing that photographs taken in an inertial reference frame near traveling near c relative to another observer wouldn't show relativistic effects within that frame - he was arguing that it's impossible to have a spaceship traveling near c to begin with, so the question is moot. If you read my original post in this thread you'll see that I'm well aware of the principle of relativity.

Last edited: Aug 23, 2011
15. Aug 23, 2011

### nitsuj

I'd like to point out I said specifically the answer is moot.

I never read the definition of moot until now.

http://www.merriam-webster.com/dictionary/moot" [Broken]

Doesn't make sense? It could define moot.

Last edited by a moderator: May 5, 2017
16. Aug 23, 2011

### nitsuj

I don't know. Is it?

Is it possible for there to be a ship with two people on board with a camera all traveling "infinitely close to the speed of light" and take a photo?

And at the same time on a planet passed by the ship a camera takes a photo of the ship while it passed by at "infinitely close to the speed of light"?

And that photo to show relativistic effects?

Sounds rather abstract and deprived of practical significance.

17. Aug 23, 2011

### elfmotat

Why do you think thought experiments should be limited to the practical? Would you prefer the scenario "say there's a mu-meson particle moving at..." ? I don't really understand what your point is.

18. Aug 23, 2011

### Pengwuino

Yes, but that's like saying "what if I had a fusion powered rocket strapped to a 9 headed alien who eats glue and mates with cows. A cow attempts to take a picture of this fusion powered alien from Earth as it flies by.....". These abstract concepts are simply human methods of imagining what is going on. Just because the description is not practical or possibly even silly doesn't mean we can't use it to understand what is actually happening in the universe. We just know that instead of a 9 headed alien traveling by Earth, we have a proton slamming into a target in a high energy physics experiment.

19. Aug 24, 2011

### nitsuj

Here is the OP's question

"Say two people are on a spaceship travelling at near speed of light. If one wants to take a picture of the other, would that be possible?

EDIT: The picture would be taken by the person in the rear of the craft, facing the front."

After givin a moot answer...

The OP left with "Much less exciting than what I was hoping, but thanks :P".

So the OP belives a photo can be taken at near c speeds on a spaceship.

Perhaps the OP would have found it even less exciting to hear the impossibilities of accelerating a spaceship with people on board to near c speeds.

20. Aug 24, 2011

### elfmotat

And rightfully so, because a photo CAN be taken at speeds near c on a spaceship - whether or not we can build such a spaceship is irrelevant. OP's question was about the principle, and he was given an answer. I'm starting to think you're trolling me...

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