Relativistic quantum mechanics / time machine question?

Don't really care about wave functions. But a pair of entangled photons, each with some unspecified spin, can be used to send information...contrary to what the texts will tell you about information limited to light speed.

Here, tell me what this tells you (the information).

***---******---*** [See source.]

Each * is a change in spin direction for both photons. Just a change, don't care which direction. And the wave functions can collapse all they want. All we need is a super precise and sensitive device to sense the spin changes and record them.

As to time travel, not likely. Because time is the unfolding of events, only current time exists. Past time is made of events that have happened; they no longer exist. And future time is made of event that are yet to happen; it doesn't exist either. And scrub the time dilation concept; the best one can do with that is catch up with the current time, now, in the static reference frame.

One way to think of entanglement is to think about individual states of the entangled particles. In that picture, the wavefunctions have to collapse instantaneously - regardless of the distance separating the particles. This seems to violate causality which all of physics is built on. It was one of Einstein's fundamental objections to quantum theory.

But another way, which is more in the spirit of quantum theory, is to recognize that the entangled system is the quantum system and it has states (2 or more - let's stick with two possible states). The system (the two particles) can be found in either state with some probability associated with each state. Now when you measure one particle, you are collapsing a wavefunction of the system - you have forced the system into one of its states. It gets around, in a fashion the notion the two particles communicate through some back channel exempt from causality.

Since we know of no real violation of causality, relative motion doesn't help. Also, I don't see how you can use the wavefunction as on or off - if you observe the wavefunction (i.e. make a measurement) you collapse it. You can't observe the wavefunction without collapsing it so there is no point in trying to use the uncollapsed function for signaling - you wouldn't know it was there because you haven't measured it.

I don't need to peruse your link. The basic premise that you can somehow send information through quantum entanglement is flat out wrong. If you have a physics degree then you should be able to understand the following link, http://en.wikipedia.org/wiki/No-communication_theo...

As for sending information " where collapsed/uncollapsed wave functions serve the role of the on-off tone" is nonsense. You can't tell the difference between a collapsed and non-collapsed state since you are ALWAYS measuring a collapsed state (at least the part of the total state vector that you are trying to use for communication).

"Relativistic quantum mechanics / time machine question?"

"[As a heads up, If you do not have a degree in physics or are at least working on one, this question will be out of your depth. Please refrain from answering.]"

Sorry, but you do not get to place this requirement. I do not qualify, so please feel free to ignore.

"Basically, I do not see why quantum entanglement + relativity of simultaneity cannot be used to produce a time machine."

Entanglement, occurs between systems of particles *now*, not over some disjoint in time.

"Entanglement: Use the fact that the wavefunctions of entangled particles collapse simultaneously to send messages using Morse code, where collapsed/uncollapsed wavefunctions serve the role of the on-off tone. This should be able to send information instantaneously (see details in link)."

Instantaneously, to spatially separated points.

"Relativity of Simultaneity: Moving observers perceive different sets of events to be simultaneous with one another. Use a network of observers moving relative to one another and sending signals to each other to bounce a signal back in time using entangled quantons."

Fails to send anything "back in time". For any finite signal propagation speed, the signal arrives at the destination in forward time. Given infinite speed, it arrives at the instant of transmission. Still not "back in time".

...

"I asked my professors about this back in undergrad, but never received a real answer."

Frankly, I do not see where you think all observers that correctly map between two events, and all agree on them to be simultaneous in all frames, will think something went backwards in time.

"You really are going to have to at least skim through the link before answering."

Not if you described it here correctly. I do not give questioners my IP address, just because you might think I need to.

The plausible impossible? Next time I take out my slide rule.....ever take two tops and spin them in opposite directions on carbon paper (if you can locate any) ?? Those are real experiments, provable but theoretically similar. Go have fun with it, plant ideas, I am retired...Ellie