Questions
I have received many questions related to Quantum Entanglement, and have done my best to answer them.
Q: Is spin the same as charge?
No.
Q: Can we use entanglement for instantaneous communications?
No. Current theories suggest that the information passed between particles
in an entangled system must remain a secret. However, experiments involving
the decay of radioactive particles may hold promise for detecting when one
half of an entangled pair has changed.
Q: If a virtual "point" was on a particle, would it move in a direction
that correlates to its spin?
No. To my understanding, this is like saying, "If I have a solid green ball,
and I rotate up, will its shaded bottom move to the top?" Colour, like spin,
is an intrinsic part of the ball. Let me explain a bit further.
Two particles of the same type, but with differing spin, is like having two colours for balls. They are both the same type (a ball, or a photon), but one of their intrinsic properties (colour, or spin) is different. There really isn't a classical analogy for spin.
Q: Does sending entangled photons through two different mediums produce
Einstein's Twin Paradox?
No. From the observer's point of view, the entangled photons will have
travelled different distances. From the point of view of the photons, they
have both travelled the same distance. As particles travel faster, time
slows down. Photons, at 3 x 108 m/s, do not experience time.
Q: Don't the photons already know their relative polarizations upon creation?
Maybe. This is an item that, to my knowledge, is still being debated. A better
example would have been to use the direction of travel. Changing which way
one half of a two-photon entangled system is headed will instantaneously
affect the other (until measured, at which point the waveform collapses,
and hides all that precious information with it).
Q: Do particles passing through a magnetic field move in/out and up/down?
Yes. If they are charged particles, they will move both in and out as well
as up and down.
Q: How does photon spin really work?
To my understanding, an object can spin in a large number of directions (on
order of 1033). However, particles have limits to the amount of
spin that can be applied. Once we choose an axis there are only 2J + 1 ways
to put a fraction of spin on the particle. (The value of J can be ½,
1, 1½, or 2 depending on the particle.) So for a spin ½
particle, the units are +½ or -½, which are known as
spin up and spin down.
For a massless spin 1 particle, it can be +1, 0, or -1. For a spin 1 particle (e.g., a photon) travelling at the speed of light, the only axis worth mentioning for orienting the spin of the particle is its direction of motion. Since 0 spin is meaningless (it would indicate the axis does not exist), people talk about these partilces in terms of spin +1 or -1, which are also sometimes referred to as spin up and spin down, but I prefer to use the distinguishing terms left-handed and right-handed.
Q: Can magnets bend light?
No. Technically, under certain circumstances, a photon can split into an
electron and positron (an anti-electron). When split, the magnetic field
can then influence the electron-positron pair. As soon as they merge into
a photon, the photon's direction will have changed. Thus the net effect is
that the magnet appears to have bent light, but in reality, it has deflected
an electron-positron pair.
Q: Do electrons and positrons have mass?
Yes. E=mc2 hints to how that conversion is possible. The
electron-positron pair from the previous question would have enough mass
to satisify Einstein's equation such that E is equal to the amount of
energy possessed by the original photon. Furthermore, the mass of an
electron and positron are exactly the same.
Q: Do electrons travel at the speed of light?
No. When electrons travel through a vacuum, they can travel quickly, but not
at light speed.
Q: How do physicists know entanglement works over billions of miles?
To date, researchers have only observed the effects of quantum entanglement
over a distance of several miles ... since we don't have the technology
to observe the effect first-hand at distances spanning much more than that
of the Earth and Moon.
However, a cosmological experiment was done using quasar 0957+561A,B (Entanglement, The Greatest Mystery in Physics, by Amir D. Aczel pp.92-93) that showed how a photon can simultaneously travel two paths across great distances. A galaxy splits the space between Earth and the quasar, acting as a gravitational lens, thus creating two light rays separated by 50,000 light years. When we observe the arrival of a photon we can, by using half-silvered mirrors, determine which ray the photon travelled or whether it travelled both rays. What makes this experiment interesting is that when we put in the silvered mirror (or not), the photon has already passed the galaxy! In effect, we wind up changing history. I urge you to read Dr Aczel's book for details.
This doesn't show that the effects of entanglement persist across great distances, but it does serve to illuminate that some quantum behaviour is consistent at these lengths.
