You don't need any mathematical calculations to see that the two statements
The laws of physics don't depend on the inertial reference frame
There's an upper limit to the possible velocities
imply that this upper limit must be the same in every reference frame, and thus anything going at that speed does so in every reference frame. That's elementary logic.
Photons can send states, you can send binary ascii this way. therefore send classical information foreward, very easy to do and then use that classical information to send backwards through the limited communication medium.
Sorry, but it doesn't work that way. You have to send the classical information from the sender to the receiver (because it's at the sender where it is generated). That classical information also isn't "extra", by itself it is just as random as the measurement results on the quantum system. Only if you combine both, you get transmission of information.
There are several proposals (and calculations) about entangling (microscopic, but still large compared to typical quantum systems) cantilevers, but I'm currently not aware of an experiment which already did this (and didn't find any with a quick Google Scholar search).
If you look at the paper closely, you'll see that it derives that under the given assumptions you get either SR (Lorentz transformation) or Newtonian space and time (Galilei transformations). The fact that he terms Galilei symmetry as degenerate Lorentz symmetry (which is mathematically true) doesn't change the fact that this argument doesn't decide between the two options. It only excludes that there's a third option.
Oops, I just notice I mixed up the terminology: It's of course not a Bell measurement (although a Bell measurement is involved in the teleportation/"entanglement swapping" step), but the measurement of a Bell inequality violation.
Can we use this trick to create closed time loops?
No.
B sends message to A using ordinary speed-of-light (or even speed-of-sound) communications.
OK, no problem in this step.;-)
A sends the message back in time to B, via entangled photons, since B can measure his photon before A's photon ever existed.
No. You cannot send a message just using entangled photons. You always have to send classical information along in order to communicate. So to use entanglement for sending information into the past, you'll first have to solve the problem of sending classical information into the past.
Think of the entangled photons as being an encryption key. It doesn't help you if you get the encryption key, as long as you don't also get the encrypted message.
No, it's not a measurement error. It's exactly what you'd expect from such a setup, without assuming entanglement over time. However, if they had described this experiment as what it actually is, a standard Bell measurement where one of the photons was quantum-teleported before measuring it, but after having measured the other photon, I'm sure it would not have generated much interest.
Actually de Broglie-Bohms unobservable particle trajectories are the exact equivalent to the epicycles: Additional complications, introduced to save certain assumptions on the world (epicycles: only circular motion, with the earth in the center; Bohm trajectories: movement of well-localized particles in space).
Also, de Broglie-Bohm is incompatible with special relativity.
Lorentz transformations only cover special relativity. In general relativity, you can indeed have the distance between two points grow faster than light. Of course not if the points are at the same place.
Actually, there's a very simple interpretation of this experiment which doesn't need entanglement over time at all:
First, you create a normal entangled pair (no over-time entanglement involved).
Then, you measure one of the photons, breaking entanglement. The other particle now has the corresponding state. If we were to measure it immediately, we'd find the correlations with the first photon we use to detect entanglement that was present before the first measurement.
But we don't immediately measure it, but we use a second pair of entangled photons to quantum-teleport it. Note that there's no entanglement swapping going on here, because there's no longer entanglement in the first photon. It's just normal quantum teleportation (well, actually entanglement swapping is also just quantum teleportation of an entangled particle). Of course the teleported photon has the same state as the non-teleported.
Now the teleported photon is measured. Of course we find the correlations with the first-measured photon. That doesn't mean this photon was ever entangled with the original one.
Read it an weep, I'd be sacked if ever I did that, yet their network admins seem to think it's an 'improvement':
"Grid operations and control systems are increasingly automated, incorporate two - way communications, and are connected to the Internet or other computer networks. While these improvements have allowed for critical modernization of the grid, this increased interconnectivity has made the grid more vulnerable to remote cyber attacks."
So they took a critical system and connected it to every hacker and script kiddie on the planet, knowing that botnets endlessly test every IP address for vulnerabilities. And they complain about botnets testing the stuff THEY CONNECTED to the internet! WTF.
It's a case of incompetent sysadmins, couples to a self serving 'cyber-war' agenda on behalf of the people who should be advising them to disconnect them from the internet!
Something similar happened to me. I figured out that putting all my money in front of my door would be quite useful because I'd just take some of it when I leave the house, and I don't need my money inside anyway. However as soon as I did so, people just started to take away my money lying there! Who would have thought that!
If you exist on one side of the galaxy at one moment, and on the other the next, this does not mean you traveled a path between the two points in three-dimensional space as we understand it. Should there be a means to complete that positional change without passing through the space between, then acceleration and velocity do not come into play at all, and so neither does special relativity.
Wrong. Relativity is a theory about spacetime, and thus everywhere spacetime is involved, relativity is involved.
Specifically, the causality violations do not occur due to accelerations or due to continuous movement at FTL speed, they appear whenever there's a causal relation between spacelike separated points in spacetime. A controlled FTL journey, no matter if continuous or as jump, implies such a causal relation. Indeed, even FTL communication does.
The only way to get FTL travel or FTL communication of any kind without violating causality would be if the mechanism violates relativity.
Slashdot Mirror
You don't need any mathematical calculations to see that the two statements
imply that this upper limit must be the same in every reference frame, and thus anything going at that speed does so in every reference frame. That's elementary logic.
Sorry, but it doesn't work that way. You have to send the classical information from the sender to the receiver (because it's at the sender where it is generated). That classical information also isn't "extra", by itself it is just as random as the measurement results on the quantum system. Only if you combine both, you get transmission of information.
There are several proposals (and calculations) about entangling (microscopic, but still large compared to typical quantum systems) cantilevers, but I'm currently not aware of an experiment which already did this (and didn't find any with a quick Google Scholar search).
But the encryption key is completely random.
The double-slit experiment can be done with electrons and atoms.
And with C60 molecules.
Also, ions have been entangled.
If you look at the paper closely, you'll see that it derives that under the given assumptions you get either SR (Lorentz transformation) or Newtonian space and time (Galilei transformations). The fact that he terms Galilei symmetry as degenerate Lorentz symmetry (which is mathematically true) doesn't change the fact that this argument doesn't decide between the two options. It only excludes that there's a third option.
Oops, I just notice I mixed up the terminology: It's of course not a Bell measurement (although a Bell measurement is involved in the teleportation/"entanglement swapping" step), but the measurement of a Bell inequality violation.
No.
OK, no problem in this step. ;-)
No. You cannot send a message just using entangled photons. You always have to send classical information along in order to communicate. So to use entanglement for sending information into the past, you'll first have to solve the problem of sending classical information into the past.
Think of the entangled photons as being an encryption key. It doesn't help you if you get the encryption key, as long as you don't also get the encrypted message.
No, it's not a measurement error. It's exactly what you'd expect from such a setup, without assuming entanglement over time. However, if they had described this experiment as what it actually is, a standard Bell measurement where one of the photons was quantum-teleported before measuring it, but after having measured the other photon, I'm sure it would not have generated much interest.
Actually de Broglie-Bohms unobservable particle trajectories are the exact equivalent to the epicycles: Additional complications, introduced to save certain assumptions on the world (epicycles: only circular motion, with the earth in the center; Bohm trajectories: movement of well-localized particles in space).
Also, de Broglie-Bohm is incompatible with special relativity.
Lorentz transformations only cover special relativity. In general relativity, you can indeed have the distance between two points grow faster than light. Of course not if the points are at the same place.
Actually, there's a very simple interpretation of this experiment which doesn't need entanglement over time at all:
First, you create a normal entangled pair (no over-time entanglement involved).
Then, you measure one of the photons, breaking entanglement. The other particle now has the corresponding state. If we were to measure it immediately, we'd find the correlations with the first photon we use to detect entanglement that was present before the first measurement.
But we don't immediately measure it, but we use a second pair of entangled photons to quantum-teleport it. Note that there's no entanglement swapping going on here, because there's no longer entanglement in the first photon. It's just normal quantum teleportation (well, actually entanglement swapping is also just quantum teleportation of an entangled particle). Of course the teleported photon has the same state as the non-teleported.
Now the teleported photon is measured. Of course we find the correlations with the first-measured photon. That doesn't mean this photon was ever entangled with the original one.
That code isn't bug-free. It's just insufficiently tested.
So you think all Brits are idiots?
Read it an weep, I'd be sacked if ever I did that, yet their network admins seem to think it's an 'improvement':
"Grid operations and control systems are increasingly automated, incorporate two - way
communications, and are connected to the Internet or other computer networks. While these improvements have allowed for critical modernization of the grid, this increased interconnectivity has made the grid more vulnerable to remote cyber attacks."
So they took a critical system and connected it to every hacker and script kiddie on the planet, knowing that botnets endlessly test every IP address for vulnerabilities. And they complain about botnets testing the stuff THEY CONNECTED to the internet! WTF.
It's a case of incompetent sysadmins, couples to a self serving 'cyber-war' agenda on behalf of the people who should be advising them to disconnect them from the internet!
Something similar happened to me. I figured out that putting all my money in front of my door would be quite useful because I'd just take some of it when I leave the house, and I don't need my money inside anyway. However as soon as I did so, people just started to take away my money lying there! Who would have thought that!
We demand that NASA's Alpha Magnetic Spectrometer may or may not have detected dark matter!
He already gets that. Ho got no prayer delivered for the last 500 years!
I can imagine a solution which doesn't need operating a server ... but mentioning it might attract apk. :-)
As soon as it comes into contact with the patient, it's no longer sterile, and can no longer be used for another patient without a new sterilization.
I guess that would not fly very well in marketing. The customer would run away before you reached the end of that version number.
You know it's possible to have a woosh, right?
No, only a whoosh. :-)
An absurd Three Letter Agency, of course.
Two General Intermediate ReLeases, one Critical Update Patch! :-)
If you exist on one side of the galaxy at one moment, and on the other the next, this does not mean you traveled a path between the two points in three-dimensional space as we understand it. Should there be a means to complete that positional change without passing through the space between, then acceleration and velocity do not come into play at all, and so neither does special relativity.
Wrong. Relativity is a theory about spacetime, and thus everywhere spacetime is involved, relativity is involved.
Specifically, the causality violations do not occur due to accelerations or due to continuous movement at FTL speed, they appear whenever there's a causal relation between spacelike separated points in spacetime. A controlled FTL journey, no matter if continuous or as jump, implies such a causal relation. Indeed, even FTL communication does.
The only way to get FTL travel or FTL communication of any kind without violating causality would be if the mechanism violates relativity.
If you go to that level, why not go the full way and implement closed timelike curve computing?