Quantum Mechanics

Ok you said the path has changed, the speed of light has not. Fine, but communication at faster than the speed of light is possible by warping space. Therefore speed of light is not a final barrier. The maximum speed of light in a vacuum could be as important in the grand scheme of things as the maximum speed of a ship on the high seas.

Hi.
This is probably a stupid question but can someone tell me:
Does Quantum Mechanics violate causality in any way.
I know the generally-accepted interpretation is that QM is indeterministic.
But isn't indeterminism still causal?
(As determinism is causal).

I suppose what i'm wondering is:
If you do a measurement in QM with the exact same settings, will the answer be exactly the same or does the randomness in QM mean the answer will always be different.
And even if it was, is this reconcilable with causality.

Sorry if this comes across as an elementary query.
It's just bugging me a bit.
Thanks.

It's a good question. If the one of the pair could be activated (read) only by a specific wavelength (for instance a signature of a supernova) and then the entangled partner back on earth have an instantaneous change. This could provide an early warning system of supernova radiation advancing towards Earth at the speed of light.

The transmission of information would in this case be in the sensing of the change of the entanglement rather than encoding any specific signal.

However I think one sticking point is you need to actively read (I don't think there is a mechanism for a passive output) the entangled partner back on Earth. I've not been able to get a clear answer to this yet before Professors and their ilk start diving down the black tunnel of quantum mechanics.

An answer from another forum
'Because there is no apparent correlation until measurements are compared, the states will be observed in whatever reference frames they're observed in, and no one will agree on who observed first. But they will agree, when they compare measurements, that there was entanglement.'

So you would have to read the partner on Earth to determine it's state, but you do not know if the entangled partner in space has been read first or not. There is no signal like 'green' or 'red' that can be programmed into the entangled state, it will just give a random assortment of 'greens' and 'reds' when you read them. It's only when you communicate using slower than light speed that you can get information as to when the other observer made their observation and therefore who was actually first to observe. That's my understanding of it, could be wrong though.

Thanks for your reply maninaisa.

I guess I was a bit confused by the concept of quantum entanglement as I thought once 2 diamonds were entangled, one could be manipulated and it would affect both and figured this could be used to transmit information in binary - inactive state and manipulated. So I guess I misunderstood the "manipulated" piece.

Fount the article
Walmsley and his colleagues set up an experiment that would attempt to entangle two different diamonds using phonons. They used two squares of synthetically produced diamond, each three millimeters across. A laser pulse, bisected by a beam splitter, passes through the diamonds; any photons that scatter off of the diamond to generate a phonon are funneled into a photon detector. One such photon reaching the detector signals the presence of a phonon in the diamonds.

But because of the experimental design, there is no way of knowing which diamond is vibrating. "We know that somewhere in that apparatus, there is one phonon," Walmsley says. "But we cannot tell, even in principle, whether that came from the left-hand diamond or the right-hand diamond." In quantum-mechanical terms, in fact, the phonon is not confined to either diamond. Instead the two diamonds enter an entangled state in which they share one phonon between them.

To verify the presence of entanglement, the researchers carried out a test to check that the diamonds were not acting independently. In the absence of entanglement, after all, half the laser pulses could set the left-hand diamond vibrating and the other half could act on the right-hand diamond, with no quantum correlation between the two objects. If that were the case, then the phonon would be fully confined to one diamond.

If, on the other hand, the phonon were indeed shared by the two entangled diamonds, then any detectable effect of the phonon could bear the imprint of both objects. So the researchers fired a second optical pulse into the diamonds, with the intent of de-exciting the vibration and producing a signal photon that indicates that the phonon has been removed from the system. The phonon's vibrational energy gives the optical pulse a boost, producing a photon with higher energy, or shorter wavelength, than the incoming photons and eliminating the phonon in the process.

The reread helped, I had assumed after entanglement that vibrations in one diamond would translate to the other one offering a way to communicate but they are entangled because they are both vibrating when only one should be.

southcentralts wrote: »

Because they are entangled, information can theoretically be passed between them faster than the speed of light ( or so my understanding of the subject goes),

No, entanglement can not be used to transmit information in any way.

I'm reading a few books on quantum mechanics at the moment . How can quantum entanglement occur after particles exsist?

could make up some of these things your self

I don't think the fish would be happy ?

SB