Can information travel faster than light?

[yuiop]

I would not go as far as calling that a fact.

At any rate this discussion seems to be appropriate in the Quantum Mechanics section of this forum.

I think discussing the faster than light communications of entangled particles is very relevant to a thread titled "Can information travel faster than light?".


Entangled particles communicating faster than light is the simplest explanation. Bell said and experiment prove that there is no explanation of quantum entanglement experimental observations that is both local and realist. Local means that entangled particles are limited to communicating at the speed of light. If you insist on an explanation that does not require entangled particles to communicate faster than the speed of light then you have to accept a non-realist explanation.

Non realist explanations include:

a) Determinism: Anne and Bob (or any of us) have no free will and what measurements they carry out is predetermined even before the entangled photons are emitted or that the entangled photons rather than influencing each other influence the minds and decisions of Anne and Bob.

b) Many Worlds: Every time a measurement is made the universe splits of into parallel realities covering all possible outcomes and then somehow discards the parallel worlds where the outcomes do not agree with quantum rules.

c) Time manipulation: If the outcome does not agree with quantum rules then the universe rewinds erasing all memory of the quantum violation and has another go until it gets it right. Alternatively, when Anne or Bob make a measurement a signal goes back into the past causeing a photon (of the correct tiype) to be emitted. In this way the future causes the past rather than the other way round that most of us fondly imagine.

Bell's theorum basically means you have a stark choice. Either you have to believe that quantum mechanics allows faster than light communication at the quantum level or you have to believe one of the even wierder and more complex non-realist explanations.

The non-local pill is easier to swallow when you realize that just because entangled particles can communicate or influence each other faster than the speed of light it, the effect does not allow sentient observers to communicate information about events faster than the speed of light.

 

[DaveC426913]

What would cause steel, or say I make it from diamonds, to loose it's rigidness?

You're misunderstanding. Steel and diamond only seem rigid from the scale of humans. Moving one end only seems to move the other end instantly because we can't detect such a short delay.

If you have a one foot length of steel and you moved one end of it, the other end would not move until 0.000067 seconds later. If the bar were diamond, the delay would only be 0.000025s.

This is the way of all solid matter.


http://hyperphysics.phy-astr.gsu.edu/Hbase/Tables/soundv.html

 

[Sam G]

If you have a one foot length of steel and you moved one end of it, the other end would not move until 0.000067 seconds later. If the bar were diamond, the delay would only be 0.000025s.

Dang, I didn't know that. Thanks for the link ...this is heavy stuff!

 

[yuiop]

In an earlier post I suggested that entangled photons can effectively communicate with each other at faster than light speeds in a manner that described as "causal". One objection to anything communicating instantaneously is that if one observer sees event A causing effect B then another observer in a different reference frame will see effect event B before cause event A happens. This is obviously ridiculous and in many caes it violate the second law of thermodymics. It turns out that as far as communicating entagled photons are concerned there is a symmetry involved and the reversal of cause and effect for entangled photons is always plausible. If Anne measuring Up spin in her entangled particle causes Bob's particle to have Down spin, then there is no difference if Bob makes the first measurement and his observation of Down spin in his entangled particle causes Anne's entangled particle to have Up spin. It is only when larger systems of interacting particles are considered that the second law of thermodynamics comes into play. If Anne fires a gun at Bob causing Bob to die then it would not be reasonable for any observer to see the death of Bob causing Anne to pull the trigger of her gun at a later time. This would not be a good defence for Anne if she is charged with Bob's murder

Just to recap, in case there is any confusion. The faster than light communication between entangled particles does not enable sentient obervers such as Anne and Bob (when he was alive) to communicate information about events at faster than light speeds. The universe seems to differentiate between the communication channels open to simple quantum particles and the channels available to sentient observers. The dividing line seems to be the complexity of the systems. If we assume that sentient beings that can analyse, compute and predict are effectively computing systems then there must be a minimum complexity to a computing system that takes the system out of the quantum regime due to decoherance of the interacting particles of the complex system. From this, it could possibly be concluded that the observers of special relativity have to be sentient observers and a single entangled photon does not qualify as a sentient observer and the rules of special relativity do not apply to entangled photons.

 

[russ_watters]

Dang, I didn't know that. Thanks for the link ...this is heavy stuff!

I bet you did know it, you just didn't realize it: a spring has a certain elasticity and you clearly understand that - use a stiffer material or make the coils thicker and the whole spring gets stiffer. I'm sure you understand this. What holds you up is extending that concept. If the spring bends (not enough to cause permanent deformation), what happens inside it? The part on the outside of the bend must expand and the part inside must contract, right? So you know that the molecules can get pulled apart and pushed together as you bend a piece of metal. Why not also when you just push on a straight rod of the same material?

A lot of what understanding science is is understanding the domain of applicability of a concept and being able to expand the idea to cover it's whole domain. And also to not overexpand it.