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A Collision at the Speed of Light


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If an object collided into another object at the speed of light, say a planet or something, would it release infinite energy? If it was travelling at the speed of light, it would have infinite energy stored in it. So if some of it were to be annihilated, there would be infinite energy, right? Any help would be appreciated :)

Thanks,

Corkey

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yes, but that is not possible.
if an object has infinite energy, then it would collapse into a black hole, which would be infinitely big and would gulp the entire universe instantaneously, right?
Your thought experiment leads to weird conclusions. That's why no object with mass can move at the speed of light.

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Just now, kilix said:

yes, but that is not possible.
if an object has infinite energy, then it would collapse into a black hole, which would be infinitely big and would gulp the entire universe instantaneously, right?
Your thought experiment leads to weird conclusions. That's why no object with mass can move at the speed of light.

Yes, relativity does mean that no massive object can travel at the speed of light. But we're talking hypothetical stuff

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There are a couple of things up with that question, for example:

1) Infinity is not a great word in physics, it would upset all sorts of proven theories - including the one that your hypothetical situation is about (E=mc2) :)

2) Matter cannot travel at LS, for it to do that would require infinite energy (see #1).

3) Its a hypothetical situation that goes against the laws of thermal dynamics (you cant get something for nothing).

 

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Just now, Uranium235 said:

There are a couple of things up with that question, for example:

1) Infinity is not a great word in physics, it would upset all sorts of proven theories - including the one that your hypothetical situation is about (E=mc2) :)

2) Matter cannot travel at LS, for it to do that would require infinite energy (see #1).

3) Its a hypothetical situation goes against the laws of thermal dynamics (you cant get something for nothing).

 

Thanks for the help! I know someone who made a video about things colliding at light speed, so I just wanted to see if it could even happen at all.

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7 minutes ago, Corkeyno2 said:

Yes, relativity does mean that no massive object can travel at the speed of light. But we're talking hypothetical stuff

but... how do you imagine infinitely energetic collision?
that leads to an infinitely huge black hole again (E=mc2).
That question can not be answered normally unless you disregard all physics and move to a land of fantasy.

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Just now, kilix said:

but... how do you imagine infinitely energetic collision?
that leads to an infinitely huge black hole again (E=mc2).
That question can not be answered normally unless you disregard all physics and move to a land of fantasy.

This is exactly what I need. A YouTube guy told me that a collision like this could happen, but now I can prove him wrong. Thanks!

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Just now, Corkeyno2 said:

This is exactly what I need. A YouTube guy told me that a collision like this could happen, but now I can prove him wrong. Thanks!

you created a topic on SGL to win in a YT fistfight :D
you made my day.

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36 minutes ago, Corkeyno2 said:

If an object collided into another object at the speed of light, say a planet or something, would it release infinite energy? If it was travelling at the speed of light, it would have infinite energy stored in it. So if some of it were to be annihilated, there would be infinite energy, right? Any help would be appreciated :)

Thanks,

Corkey

This can only happen if the "object" had zero rest mass e.g. a photon. This happens all the time when one is absorbed by an atom.

Other than that, as above, it can't happen.

Regards Andrew

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41 minutes ago, Corkeyno2 said:

If an object collided into another object at the speed of light, say a planet or something, would it release infinite energy? If it was travelling at the speed of light, it would have infinite energy stored in it. So if some of it were to be annihilated, there would be infinite energy, right? Any help would be appreciated :)

Thanks,

Corkey

So both the objects would have infinite energy?

But each object would have less than the amount of energy in both objects...

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5 minutes ago, Alien 13 said:

I am a total novice with this branch of physics but dont the laws prevent acceleration of an object with mass** up to LS but not one that is already traveling at those speeds or higher?

Yes.

** technically : "with non-zero rest mass"

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Don't get too excited about the term "infinite", it's nothing more than a mathematical operator that points to a gap in our understanding. Physicist hate it when the maths points to "infinite". Reality is much more complicated and interesting than the dead end of infinity on the other side of the equal sign. :) 

Jim

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Questions like these do not have "concrete" answers because they represent scenarios that cannot exist.  It's like the old schoolkid question: What happens when an irresistible force meets an immovable object?  Answer: nothing, because these things do not exist.  Infinities are mathematical notions that do not transfer into practicality.

Doug.

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This brings me back to Physics class... :D This question seems to have been answered sufficiently and i don't want to sound like an echo :p We were lucky and had a Physics teacher who had a great interest in the Universe and we would sometimes ask him questions like this... This sort of thing still makes my head hurt though, not because i don't understand it, but because "what if" questions flood your mind!

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11 hours ago, saac said:

Don't get too excited about the term "infinite", it's nothing more than a mathematical operator that points to a gap in our understanding. Physicist hate it when the maths points to "infinite". Reality is much more complicated and interesting than the dead end of infinity on the other side of the equal sign. :) 

Jim

Unfortunately Jim, all our theories in physics are just a set of mathematical operators connecting "entities" of the theory with one another. Infinity has just a good an underpinning mathematically as do the differential operator, the delta function and matrix inversion. (I was going to add set theory but that has real problems with self reference.)

I think it is more a matter of familiarity or not with particular mathematical concepts that excites and exercises  us.

Reality is what it is and we do our best to tame it with our theories to make the world predictable.

Regards Andrew

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15 hours ago, Stub Mandrel said:

So both the objects would have infinite energy?

But each object would have less than the amount of energy in both objects...

No they wouldn't.  Both objects would have an infinite amount of energy before the collision, and an infinite amount of energy would be released by it.

Maths tells us:

∞ + ∞ = ∞

∞ ÷ 2 = ∞

To make that a bit more concrete, let's make a set of integers by following some simple rules:

  • Start with 1, make it a member of the set. 
  • Now add 1 to 1 and make it a member of the set.
  • Take the result of the previous step, add 1 and make it a member.  Repeat this step.

Wherever you get to, you can always add 1 and get another number.  Therefore the resulting set {positive integers} has an infinite number of members.

Now make another set of integers:

  • Start with -1, make it a member of the set. 
  • Now subtract -1 from -1 and make it a member of the set.
  • Take the result of the previous step, subtract -1 and make it a member.  Repeat this step.

Similarly we end up with the set {negative integers}, which also has an infinite number of members.

Now let's take the union of {positive integers} and {negative integers}:

{positive integers} ∪ {negative integers} = {integers excluding zero}

So how many members are there in {integers excluding zero}?  You got it, an infinite number of members.  If we created {positive integers} through a process of repeated additions of 1 and got to ∞ members, it follows that we must have created {negative integers} through the same number of repeated subtractions of 1.  Therefore {positive integers} and {negative integers} must contain the same number of members, and {integers excluding zero} must contain twice as many members.

That's infinity for you.  Seems unlikely that we will be encountering any objects with mass travelling at the speed of light, doesn't it?

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Always confuses me a little that maths exercise. The whole well if you have a group of infinity positive integers you can always still add 1 doesnt quite stand up in my book. Surely you cant? for this reason surely if you have an infinite group of integers it already contains every integer and therefore any integer you attempt to add would already have to be a member? any new found, thought up, popped into reality integer would by definition also already be a member. Therefore there would be no integer you could add that isnt already a member?

In terms of the OP lets put it another way. Who would win in a mass bar bawl between some drunk Predator aliens and a group of rowdy bottom pinching Borg?

 

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3 hours ago, symesie04 said:

Always confuses me a little that maths exercise. The whole well if you have a group of infinity positive integers you can always still add 1 doesnt quite stand up in my book. Surely you cant? for this reason surely if you have an infinite group of integers it already contains every integer and therefore any integer you attempt to add would already have to be a member? any new found, thought up, popped into reality integer would by definition also already be a member. Therefore there would be no integer you could add that isnt already a member?

In terms of the OP lets put it another way. Who would win in a mass bar bawl between some drunk Predator aliens and a group of rowdy bottom pinching Borg?

 

You're confused because I didn't say if you had the infinite set of integers you can always add one more. Exactly the opposite in fact, if you can add one more it wasn't the infinite set. My point was that mathematically you can have two infinite sets, combine them and still have an infinite set. I was just illustrating that mathematical rules and what is possible in reality aren't necessarily the same thing.

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