archiv~1: RE: SETI Quantum Communications?

RE: SETI Quantum Communications?

Jacques.Tempere ( (no email) )
Tue, 3 Nov 1998 11:48:09 +0100 (MET)


On Mon, 2 Nov 1998, jbrown2 wrote:
> Jacques - Please clear something up for me. When a physicist, such as your
> self, says that you 'measure the state of a particle' do you mean that
> literally or figuratively?

When I say, 'measure the state of a particle', I'm being sloppy ;-)

In a classical (non-quantummechanical) viewpoint, a measurement (like
measuring the frequency, or the momentum) has a unique and predictable
In quantum mechanics, the outcome of a measurement is intrinsically
probabilistic. If you measure the position for example, you'll find that
it's a bit fuzzy - you find a distribution of positions. This has nothing
to do with your equipment, but is a fundamental property of particles.
The mathematics behind quantum mechanics allows to calculate the
probability distribution for such measurements, as well as the evolution
in time of this probability distribution. That's why I said a measurement
is like a lottery.

For the quantum teleportation experiments, I believe the measurement was a
measurement of the polarisation of the photons. wrote:
> Of course this wont work because of ..... whatever. But something might.

It doesn't work, but you're right, maybe something once might. That's the
fun of doing physics research !

Zoltan Farkas wrote:
>This discussion is very interesting, theres's just one thing not clear
>for me: in order to teleport information, the particle beam must first
>arrive at the receiver side, since you're teleporting quantum states,
>not the particles themselves.

But an advanced civilisation with a home planet and a colony could
keep a stock of twinned particles, with one member of each twin at home
and the other member at the colony. They can keep the twins and use them
whenever they want (well... there'd be an "expiry date" due to decoherence
effects). Whenever they would want to do a quantum teleportation
experiment, they can use one of the pairs 'in stock'.

It's a bit like the science-fiction 'jump gates' which bring you from one
part of the universe to another. Of course, you first have to build the
gates, bring the material there. But once the two gates are there, you can
use them whenever you want. Whenever the two twinned particles are in
their locations (home and colony), you can quantum teleport any time you

By the way, are there any sources of polarised light in the universe ?

Have a nice day (and don't get too excited over the EQ Pegasi thing - it
might have been a mistake rather than a deliberate hoax),