# No Infinite speed on information yet?

• I
• seb7
In summary, it is not possible to use the double split experiment with entangled photon pairs to communicate information at infinite speed.

#### seb7

Could someone explain why we can not use the double split experiment with entangled photon pairs as to communicate information at infinite speed? Switching off and on readers effects whether the other photons displays as interference or as particles; so why can't we use this to send 1 and 0s. (Its probably been asked before, but my searches are not turning up any answers for me.)

1 - photons being deliberately detections by D1 and recorded, thus show particles at D0
0 - photons not being recorded via D1, thus photons show interference at D0.

By firing a constant stream of photos to both D0, D1, surely we can use time to instantly send information from D1 to D0 ?

Here's a sketch, (manipulated from a similar experiment.. )

You misunderstand entanglement. The results are random so no information is transmitted. That is, if you KNOW what the state is of a particle that's going to hit D1 before it hits, then it is not entangled with anything.

It doesn't work because, as soon as the entangled partner is out there, you never see an interference pattern.

Using the measurement results from the other party, you can filter the result-not-showing-an-interference-pattern into two complementary interference patterns. But they need to tell you the measurement results, which is kind of a catch-22 if you're trying to make a mechanism for communication. You need the mechanism to communicate, but you need to communicate for the mechanism to work. Clearly not going to work very well.

There's no way of controlling the information you send (making the use of the word a bit of a misnomer), we know (or pretty sure) that the collapse of the wavefunction is 'instantaneous' now (youtube.com/watch?v=6Dp27XYjHuk) but this doesn't mean one can control what state it collapses in!

If you think carefully about what is described there you see why it's impossible by these means.