Entanglement and relitivity

[Jordan14]

Spurred by other posts I was thinking the doesn't quantum entanglement, the links between the electron and the positron, defy relivity. Because can't entanglement provide an instaneous form of communication across the whole universe.

[swansont]

Spurred by other posts I was thinking the doesn't quantum entanglement, the links between the electron and the positron, defy relivity. Because can't entanglement provide an instaneous form of communication across the whole universe.

 

No. You always need a classical channel of communication, which is limited by c. There have been other threads on this; I suggest you go read them.

[Jordan14]

Sorry about that

[5614]

normally lasers are used.... i think one day radio waves could be used as they can go longer distances and can be used via existing satelites... but that last part is my opinion.

[swansont]

normally lasers are used.... i think one day radio waves could be used as they can go longer distances and can be used via existing satelites... but that last part is my opinion.

 

Why do you say that radio waves can go further than lasers?

[5614]

well, i dont know

 

i spose they must be better than light for transmitting data purely because radios, phones and other methods of communication are all radio waves (with a tiny bit of microwaves)

 

and sure we have fibre optic cables, but i cant remember the last time someone talked over the phone using light in a satelite, for starters there'd be too much interference (i think) from all the light on this world.

 

ok, so there isnt actually a distance thing, but light isnt suitbale for send up to satelites and back. (or not as suitable as radio/micro waves)

[swansont]

well' date=' i dont know

 

i spose they must be better than light for transmitting data purely because radios, phones and other methods of communication are all radio waves (with a tiny bit of microwaves)

 

and sure we have fibre optic cables, but i cant remember the last time someone talked over the phone using light in a satelite, for starters there'd be too much interference (i think) from all the light on this world.

 

ok, so there isnt actually a distance thing, but light isnt suitbale for send up to satelites and back. (or not as suitable as radio/micro waves)[/quote']

 

OK, I see your point. Clouds would tend to get in the way of visible light. But you could still have a fiber-optic network on the earth. You aren't required to use a satellite.

[5614]

going via satelites is easier than installing mega fibre-optic cables globaly!!!

 

fibre-optic cables are quite expensive and you'd need several, i mean, you cant have one cable for all quantum internet traffic between e.g. america and the UK!

 

i mean, you'd need almost one per connection as you cant really have several light beams going down the same wire, the end computer would get confused!

 

satelites, whilst slower due to the extra journey length, would probably be more suitbale than a global fibre optic network.

[swansont]

i mean' date=' you'd need almost one per connection as you cant really have several light beams going down the same wire, the end computer would get confused!

[/quote']

 

We do this already - multiplex many light signals on the same fiber. You need to be separate the wavelengths/frequencies far enough to tell them apart (i.e. no crosstalk), but at telecom (~1550nm) you can do this with 0.4 nm or better spacing (~50 GHz). Fiber is good for a range of many nm, so you can currently get up to 32 signals on a single fiber. Research is ongoing to improve this, of course.

 

DWDM - dense wavelength division multiplexing

 

edit to add: they are trying to get to 10-20 GHz spacing as the next step; that's from a conference I went to 18 months ago. Then you go to having ~100 signals on a fiber.

[5614]

still, 32 or even approx 100 is not really enough for all of the USA --> UK communications. we'd still need many of these and one satelite would be easier and probably cheaper.

 

all the same, interesting data there... thanks.

[Guest Thangalin]

Hey,

 

There's a QE page that tells about how it works, from first principles, without math.

 

http://www.joot.com/dave/writings/articles/entanglement/

 

Ciao!

T