Recent content by wywong

In response to Omicron, UK has halved the minimum gap for booster shots from 6 months to 3 months to counter the likely reduced vaccine protection, and the new groups of people who are eligible for the booster vaccine will be invited to get a jab. I think such a blanket recommendation is not...

Many countries are urging citizens to get booster jabs early to counter Omicron. Given that a mismatched booster may render a subsequent matched booster less effective thanks to original antigenic sin (...

Thanks jim mcnamara for your reply. I find it hard to believe the same photosynthesis process discriminates against C13 but not against C14 which is heavier than C13. I did a google search and found this article...

Plants prefer C12 to C13 during photosynthesis, so that the C13 to C12 ratio in plants is less than that in the atmosphere (by around 20% for most plants, but less difference in C4 plants like maize). Do plants discriminate against C14 too? If so, won't that cause a considerable uncertainty in...

I now fully understand. Thanks folks. Really appreciate your help.

In my scenario, the absorbed photons were entangled and had opposite spins (or polarization). Now that the spins are not conserved, can the emitted photons still be entangled?

Oops! Let me correct my scenario by adding that I measure the electron spin before firing the first photon and after the second emission, and the electron spin is found to be unchanged (say both +1/2).

To make matter simple, I just assume it to have zero spin. So let's say I did and the measured spin is zero. What puzzles me is how the spin information carried by the electron can be transferred to the emitted photon given that the photon is emitted in a random direction. For example, if the...

My rationale is, although angular momentum is to be conserved, it does not follow that spin state is conserved. I do not mean linear momentum in any away affects the angular momentum. From definition, spin is the projection of angular momentum along the direction of propagation. Thus the same...

Suppose the first absorbed photon has spin = +1 and the corresponding emitted photon travels north with spin +1. Why can't the excited electron emit a southward photon with spin -1 instead? That alternative photon has the same energy and angular momentum as the actual one. They differ in...

Does the emitted photon always travel in the same direction as the absorbed photon? If not, their angular momentum can't be the same.

The total spin of the two original entangled photons is zero. Is the total spin of the emitted photons zero? Are the emitted photons entangled? I think they are totally independent.

How about this: the two photons come from an entangled pair, and they arrive at the hydrogen atom at different times because the second one takes a longer route. I do not know their spins before the absorption, and it seems that I will never be able to find out that information after the...

To prove a point. In quantum mechanics, it is said that information cannot be destroyed. I think that is not true whenever an irreversible event has taken place, as in the case of my thought experiment. Here the two bits of information encoded in the spin states seem to be lost.

Suppose I fire a photon with an upward spin towards a hydrogen atom. It is absorbed by the hydrogen atom's electron which subsequently emits a photon when it returns to its ground state. I then fire another photon with a downward spin towards the same hydrogen atom and the same thing happens...