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Traveling at Light Speed Through Space: A Thought Experiment

by michonamona
Tags: experiment, light, space, speed, traveling
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JaredJames
#19
May2-11, 07:54 AM
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Quote Quote by BruceW View Post
If Einstein's relativity is incorrect, then 'perhaps we will find a way in the future'.
Just because Einstein's relativity agrees with all experimental evidence so far, doesn't mean its impossible that someday an experiment is done that disproves the theory.
Just take a look at the LHC. Should tell you all you need to know.
mishrashubham
#20
May2-11, 08:04 AM
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Quote Quote by JaredJames View Post
Not arguing, didn't the Spitfire cross it?

(Or some old aircraft that done it in a nose dive?)
Nah just rumours. It was allegedly the P-47 but it definitely could not cross the sound barrier.
Ryan_m_b
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May2-11, 08:05 AM
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Quote Quote by BruceW View Post
If Einstein's relativity is incorrect, then 'perhaps we will find a way in the future'.
Just because Einstein's relativity agrees with all experimental evidence so far, doesn't mean its impossible that someday an experiment is done that disproves the theory.
The theory has been confirmed far beyond reasonable doubt. As JaredJames rightly says you should check out the LHC. All that power to accelerate particles as close as pos to the speed of light.

IF in the future some way is discovered to transmit mass faster than light (and I am not holding my breath) it would have to be by changing the parameters of what you are trying to do. If you could magically turn the mass of the object in question into tachyonic mass then you may have made it travel faster than light but it is no longer ordinary matter is it?

The above paragraph is to illustrate the point (FTL is not a question of breaking the theory, it would be a question of circumventing it). I in no way endorse it as a real scientific statement, don't take from it "ah then we should just find a way of doing that".
BruceW
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May2-11, 09:02 AM
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I agree that circumventing the theory or changing the parameters of what you're trying to do is the most likely way that speeds greater than c would be achieved.

But I'm also saying: imagine Einstein's laws were very slightly wrong (so slightly that current particle accelerators, which give roughly [itex] 10^{-8} [/itex] joules of energy to the particle, wouldn't be able to detect the inconsistency). Then if someone built a particle accelerator that gave the particles a much higher energy, then it might be possible for speeds greater than c to be achieved.

Einstein's relativity is almost certainly correct. But it's not completely certain. Which is why it is good to have debate on what would happen if it were wrong.
JaredJames
#23
May2-11, 09:05 AM
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Quote Quote by BruceW View Post
Which is why it is good to have debate on what would happen if it were wrong.
Well I'm sure it's a lovely debate to have, but not here. That's about as far from mainstream as you can get.
Ryan_m_b
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May2-11, 09:15 AM
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Quote Quote by BruceW View Post
I agree that circumventing the theory or changing the parameters of what you're trying to do is the most likely way that speeds greater than c would be achieved.

But I'm also saying: imagine Einstein's laws were very slightly wrong (so slightly that current particle accelerators, which give roughly [itex] 10^{-8} [/itex] joules of energy to the particle, wouldn't be able to detect the inconsistency). Then if someone built a particle accelerator that gave the particles a much higher energy, then it might be possible for speeds greater than c to be achieved.

Einstein's relativity is almost certainly correct. But it's not completely certain. Which is why it is good to have debate on what would happen if it were wrong.
That's a bit like saying "the ATM say's I have 0.05 but imagine if there was a slight calculation and it was actually 500! Let's debate that..." to a debt collector.

Imagining that what we know to the best of our knowledge is wrong and then trying to debate that can be fun but here is no place for it.
BruceW
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May2-11, 09:32 AM
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OK, I guess I was trying to start up a conversation on the meaning of science.
BTW, is there a section for that on physicsforums?
mishrashubham
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May2-11, 09:34 AM
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Quote Quote by BruceW View Post
OK, I guess I was trying to start up a conversation on the meaning of science.
BTW, is there a section for that on physicsforums?
I don't think so. PF is very strict about sticking to mainstream science.
JaredJames
#27
May2-11, 09:37 AM
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Quote Quote by BruceW View Post
OK, I guess I was trying to start up a conversation on the meaning of science.
BTW, is there a section for that on physicsforums?
You can try philosophy, but you need to follow the new rules for posting there.
Ryan_m_b
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May2-11, 09:42 AM
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Quote Quote by BruceW View Post
OK, I guess I was trying to start up a conversation on the meaning of science.
BTW, is there a section for that on physicsforums?
If it's a question related to the philosophy of science (i.e. what are the advantages of deductive empiricism?) then that could work in the philosophy section. If you just wanted to ask the question "what would the world be like if we could travel FTL?" then perhaps the general discussion forum would allow it but you'd have to read the posting rules.
BruceW
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May2-11, 09:49 AM
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Thanks for the advice, hopefully I'll be able to contribute to PF better in the future
podd
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May2-11, 09:59 AM
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Einstein's relativity works very well, but it leaves many phenomena unexplained and is based on a materialistic view of the universe which may not hold forever. Einstein's theory isn't the ultimate truth, so without getting into a "what if" debate it's still fair to say that the theory isn't certain.
Ryan_m_b
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May2-11, 10:07 AM
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Thanks for the advice, hopefully I'll be able to contribute to PF better in the future
Don't worry about it.

Einstein's relativity works very well, but it leaves many phenomena unexplained and is based on a materialistic view of the universe which may not hold forever. Einstein's theory isn't the ultimate truth, so without getting into a "what if" debate it's still fair to say that the theory isn't certain.
Theories in science have accumulated vast wealths of independent evidence all strongly indicating the theory to be true. You shouldn't complain that Einstein's theories are not the "ultimate truth", they are not meant to be. What does even "ultimate truth" mean? Einstein's theories are brilliant at describing what they are supposed to describe, nothing more.

Just because we can never say with 100% certainty that SR and GR are certain does not mean that we cannot say they are true. All evidence points towards their veracity. Look at it this way, over the centuries our understanding of the shape of the Earth has improved. When we could only measure the curvature of the horizon as 0 we believed it to be flat. Eventually better tools allowed us to measure a curvature and people thought the Earth was round. Eventually far better tools showed the Earth to be an oblate spheroid. In the future better tools may be available but is it sensible to suggest that they may show the Earth to be something entirely different than what we measure now?
ZapperZ
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May2-11, 10:11 AM
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Quote Quote by podd View Post
Einstein's relativity works very well, but it leaves many phenomena unexplained and is based on a materialistic view of the universe which may not hold forever. Einstein's theory isn't the ultimate truth, so without getting into a "what if" debate it's still fair to say that the theory isn't certain.
Then by the same token, why pick on Relativity alone? One could say that ALL science is like that! So what is this discussion about? Relativity, or Science? Is this a philosophical discussion, or a science discussion with an actual physics content (the latter is required for this thread to remain open, or to be discussed in the physics forums of PF)?

The issue I have here is that people who don't quite understand SR or even how it has worked, are producing stuff that they THINK can violate SR. This thread can't even find the proper physics forum relevant to the topic!

And for your information, there are plenty of theoretical proposals beyond just handwaving arguments or simplistic "thought experiments", of ideas that could possibly violate Lorentz invariance, etc. We continue to make such measurements to detect such violations (physicists, by nature, LOVE to find things that violates or break beyond current understanding, believe it or not).

Zz.
Physicist1231
#33
May2-11, 10:26 AM
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Quote Quote by JaredJames View Post
Unfortunately, nature cares not what you "feel". There is a heck of a lot against travelling >= C.
Thank you for that. That was awesome. There is alot that is supporting not being able to exceed C however, even the growing scientific community is talking about faster than light objects or events. IE Quantam Physics and two particles being linked together and it does not matter how far apart they are. If one particle moves the other does the same thing at the same time. So what I present is not new.

Rather most scientific breakthroughs have been achieved by thinking outside the box. And viewing something as simple as speed as a limitation is a little too "in the box".

Here is a good example. If the speed of light is the max any object (we will say a photon) can reach and that is relative to any point or object in space then what if you have two cars with cool little engines under the hood. They are X distance apart and traveling directly twoard each other at 50mph each.

Cumulitively they are approaching at 100mph.

Speed it up to 300mph each... you get 600mph closure. (Car A will see Car B approaching at 600mph)

Keep going to .25C... cumulative of .5c (no one has exceeded C yet...)

Now get to .5C each... You have a total of 1C for closure. According to Relativity this would be the limitation.

But neither one actually exceeded the speed of light. Bump the speeds up to just over .5C (which is still possible according to either newtons physics or relativity) and now you have a combined closure speed of >1C. Photons of light do this all the time say from one star to the next or even photons reflecting from the earth back in the direction of the sun. Or even simpler... two candles 5 feet from each other are emitting photons with a closure rate of the photons of 2C (excluding things like gravity, reflection, and refraction that may slow it down a little).

So >C is possible even with relativity.

You can counter this argument with Lenth and time contractions. To exclude those you have observer C that is standing equidistant from each object and measures each objects (A and B) approach and sees them both coming in at 1C apiece. He can logicly conclude that the rate of approach is 2C.... Fun stuff to think about.
Ryan_m_b
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May2-11, 10:34 AM
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Quote Quote by Physicist1231 View Post
Thank you for that. That was awesome. There is alot that is supporting not being able to exceed C however, even the growing scientific community is talking about faster than light objects or events. IE Quantam Physics and two particles being linked together and it does not matter how far apart they are. If one particle moves the other does the same thing at the same time. So what I present is not new.

Rather most scientific breakthroughs have been achieved by thinking outside the box. And viewing something as simple as speed as a limitation is a little too "in the box".

Here is a good example. If the speed of light is the max any object (we will say a photon) can reach and that is relative to any point or object in space then what if you have two cars with cool little engines under the hood. They are X distance apart and traveling directly twoard each other at 50mph each.

Cumulitively they are approaching at 100mph.

Speed it up to 300mph each... you get 600mph closure. (Car A will see Car B approaching at 600mph)

Keep going to .25C... cumulative of .5c (no one has exceeded C yet...)

Now get to .5C each... You have a total of 1C for closure. According to Relativity this would be the limitation.

But neither one actually exceeded the speed of light. Bump the speeds up to just over .5C (which is still possible according to either newtons physics or relativity) and now you have a combined closure speed of >1C. Photons of light do this all the time say from one star to the next or even photons reflecting from the earth back in the direction of the sun. Or even simpler... two candles 5 feet from each other are emitting photons with a closure rate of the photons of 2C (excluding things like gravity, reflection, and refraction that may slow it down a little).

So >C is possible even with relativity.

You can counter this argument with Lenth and time contractions. To exclude those you have observer C that is standing equidistant from each object and measures each objects (A and B) approach and sees them both coming in at 1C apiece. He can logicly conclude that the rate of approach is 2C.... Fun stuff to think about.
Entanglement offers no way for information to travel FTL (indeed nothing is travelling FTL there). As for the closing speeds two objects traveling towards each other at velocities >.5c but <1c would seem to close the distance between each other faster than if one were stationary and the other travelling at 1c but only to an observer who isn't moving relative to them. From the point of view from one of the objects the closing speed is still less than 1c http://en.wikipedia.org/wiki/Faster-...Closing_speeds

Just because objects can have closing speeds in excess of that of the speed of light does not mean faster than light speeds can be reached
DaveC426913
#35
May2-11, 10:40 AM
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Quote Quote by Physicist1231 View Post
IE Quantam Physics and two particles being linked together and it does not matter how far apart they are. If one particle moves the other does the same thing at the same time.
What exactly are you talking about?


Quote Quote by Physicist1231 View Post
They are X distance apart and traveling directly twoard each other at 50mph each.

Cumulitively they are approaching at 100mph.
No they are not. They are travelling toward each other at a hair's breadth less than 100mph. Really.

True, at anything less than relativistic velocities this is usually ignored, but since you want to get picky and scale it up, velocities do not add the way you think they do. You must use the proper velocity addition formula.


Likewise, two objects approaching each other at .9c are not travelling wrt each other at 1.98c, they are travelling wrt each other at approx .0.994c.

If they were approaching each other at .999c then there combined relative v is 0.9999994994997501.
mishrashubham
#36
May2-11, 11:06 AM
P: 605
Quote Quote by Physicist1231 View Post

Here is a good example. If the speed of light is the max any object (we will say a photon) can reach and that is relative to any point or object in space then what if you have two cars with cool little engines under the hood. They are X distance apart and traveling directly twoard each other at 50mph each.

Cumulitively they are approaching at 100mph.

Speed it up to 300mph each... you get 600mph closure. (Car A will see Car B approaching at 600mph)

Keep going to .25C... cumulative of .5c (no one has exceeded C yet...)

Now get to .5C each... You have a total of 1C for closure. According to Relativity this would be the limitation.

But neither one actually exceeded the speed of light. Bump the speeds up to just over .5C (which is still possible according to either newtons physics or relativity) and now you have a combined closure speed of >1C. Photons of light do this all the time say from one star to the next or even photons reflecting from the earth back in the direction of the sun. Or even simpler... two candles 5 feet from each other are emitting photons with a closure rate of the photons of 2C (excluding things like gravity, reflection, and refraction that may slow it down a little).

So >C is possible even with relativity.

You can counter this argument with Lenth and time contractions. To exclude those you have observer C that is standing equidistant from each object and measures each objects (A and B) approach and sees them both coming in at 1C apiece. He can logicly conclude that the rate of approach is 2C.... Fun stuff to think about.
Quote Quote by DaveC426913 View Post
No.

Relativistic velocities don't add this way. They add using this formula:

v(final) = (v1 + v2) / (1+ (v1+v2/c^2))


You will find that, when you add the ship's v (v1) and the person's jump (v2), it will always result in a number less than c.

Even if you had a 2nd stage rocket blast off from the first stage at .999c, the final v of the second stage will still be less than c (0.9999994994997501c in fact).
Just to echo what Dave has already said in this thread.


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