View Full Version here: : Question: Faster Than Light?
19-12-2010, 11:58 AM
Ok, so I've just recently rediscovered something I haven't though about for a long time, (if ever), and been proven wrong in the process !
There are phenomena which regularly exceed the speed of light:
i) The phase velocity of electromagnetic signals;
ii) The rotation velocity of a light source (say a laser light in a lighthouse), projected onto a 'screen' at large distance (say, the shoreline): when the sweep velocity is measured by two points on the shoreline, it regularly exceeds 'c';
iii) Communication between entangled quantum particles.
It would also seem that no information is exchanged in any of the above examples.
Does anyone else find this surprising … or is it just me ?
19-12-2010, 12:40 PM
The expansion of space is another example. Objects beyond a certain distance are moving away from us faster than light, making them unobservable. They are not moving through space faster than light, but the intervening space is expanding, so there is no violation of the speed limit.
19-12-2010, 12:49 PM
I believe Neutrinos travel faster than light. Hence why Neutrino are discovered before an event.
19-12-2010, 12:50 PM
I think I can deal with the faster than light-speed side of it .. but the 'no exchange of information part', has me a bit stumped.
For example, quantum teleportation has been demonstrated in 1997 (I believe).
Now, I can see that superluminal information exchange hasn't happened in this example, but information is exchanged if teleportation is declared, isn't it?
If this is the case, then surely in effect, information has been exchanged between particles, hasn't it ?
19-12-2010, 12:56 PM
I haven't read it yet but FYI - http://www.its.caltech.edu/~qoptics/teleport.html
19-12-2010, 12:57 PM
I did not think they did travel faster than light :question:, they just leave a little bit earlier than the explosion:shrug:
19-12-2010, 01:02 PM
Thanks for the clarifacation, That sort make me concerned whether it is actually possible to convert matter totravel at the speed of light. But who know what type of Physics can be discovered in the future.
19-12-2010, 01:26 PM
In quantum teleportation, the matter itself isn't transmitted or rearranged etc, BUT, the quantum information is transmitted (and can be done up to light speed). I believe this makes use of the 'shared entanglement' theorem. It would appear that the information exchange takes place via a parallel route, independent of the entangled partners, and is probably the quantum equivalent of sending an email to the recipient of the other entangled partner (at light speed, electronically).
It seems there are other quantum theorems, limiting information exchange at the quantum level .. the 'No communication' theorem, the 'No cloning' theorem and the 'No broadcast' theorem.
19-12-2010, 07:28 PM
What about Tachyon- hypothetical particle that slowest speed it can travel is speed of light.
I do believe and I stress believe that based on history and my life observation of changes in human understanding of our Universe, faster then light travel and communication will be possible some time in the future. Pity that I will not be around to see it.
19-12-2010, 07:49 PM
This is a very interesting post. i for one hope this all becomes common in the next 20 yrs. otherwise i'll miss itn all. Damit,!!!!!!!!!!!!!!
19-12-2010, 08:00 PM
If something is faster than the speed of light how do you measure it without getting into hypertheoretical physics.
In fact how fast is the speed of light. I know we can put a value on it relative to our own concept of time and distance. All we know is that it has some relative speed in our concept of being.
19-12-2010, 08:08 PM
That is a very valid point. Only recognisABLE TO US!!!
20-12-2010, 03:58 PM
If quantum entanglement experiments are explained by collapsing probability wave functions, isn't this also saying that we gain information when the wave function collapses ?
Ie: the information being the state of one or both of the entangled pair ?
20-12-2010, 04:20 PM
No information is transmitted in 'setting' the state of a complementary particle by measuring it's state. The real fact is that these particles still behave as 'one' no matter how distant they are in space. There has to be a conection at a different dimensional level.
Think about an infinite pair of scissors and then observe the intersection of the blades as they close. The intersection point is travelling faster than light. Yet no information is being transmitted as both ends are at the same place and time.
20-12-2010, 04:38 PM
I'm sure there's no information being transmitted, as you say. (It's wrapping my mind around it that's the hurdle for me).
It seems that the probability wave function, to me, is the information.
It is a little hard for me to understand how a function, modelling information, can describe the state of something and yet contain no information about when the state changes.
The scissor model would seem (to me), to bear information such as the rigidity of the scissor blade and it describing a linkage of a particular characteristic joining two points in space (??).
I think this is the same as the wave function (?). Both models encompass some type of information … otherwise we wouldn't use them (?)
20-12-2010, 07:08 PM
Yes, ive often wondered about this (in a stupid simple way), seems to me information is being transmitted faster than C.
20-12-2010, 10:50 PM
Without going deeply into the mathematics, before a measurement is performed a wavefunction is a linear combination of different states.
These states are known as eigenfunctions.
It represents a superimposed state of all possible incomes. By definition it is not composed of information, as information is obtained once the observer performs a measurement.
When a measurement occurs the wavefunction is now in the from of a constant multiplied by a single eigenfunction. The constant is known as an eigenvalue.
The eigenvalue is the information as a result of the measurement.
The initial wavefunction representing an entangled state does not contain information.
20-12-2010, 11:26 PM
See if I can make this work.....................
Faster than regular Light!
21-12-2010, 06:24 AM
This is in reality equivalent to standing on top of the lighthouse and sweeping the landscape with a jet of water. The jet would simply bend as you turn around. The sweep velocity measured would be equal to the time it takes the water to travel from the lighthouse to point B, plus the time it takes to turn from direction A to B.
With a black hole you can tell exactly where the crossover point is. Up until the event horizon the object from an observers point of view outside the black hole is still within the boundaries set by the speed of light. Once it crosses the event horizon and heads towards the singularity we cannot observe it as it travels faster than light.
21-12-2010, 12:14 PM
Hmm .. interesting … and very creative there, Andrew.
Let me apply 'The Test'…
"The litmus test is to ask whether it has or at least, could have, transmitted information. If the answer is no, the standard reasoning goes that nothing has exceeded light speed and Special Relativity survives the test."
Hmmm … a photon which has fallen into a black hole loses information via Hawking Radiation … but this happens prior to passing through the Event Horizon (?)
Might pay that one !!
(… a bit of a play on words, all of this stuff, if you ask me though).
Thanks for your input.
21-12-2010, 12:37 PM
From what I'm reading, (about the "Aspect" experiment), it appears that physicists agree that the list of possible outcomes at each of two detectors, (of entangled pairs), are identical and are correlated but there is no causation evident. This being because, in no way, can one control or predict the outcome of any particular measurement. Thus there is no message, no information whatsoever.
Very subtle interpretation here …
Hawking radiation is something completely different, and it doesn't come from the black hole per se, it comes from space just outside the black hole.
Particle/antiparticle pairs form all the time, and those near the event horizon have one of the pair sucked into the black hole. To preserve energy, the particle that falls into the black hole must have negative energy from an outside observers point of view.
From the point of view of no information being exchanged once it crosses the event horizon, this is true though! :)
21-12-2010, 12:58 PM
Yep .. this is why I agreed with you.
We should pay out on this one !!
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