1100 gamma ray bursts a day on Earth!

[Xamonas Chegwé]

It sounds like MiM wants to define gamma rays as photons produced by events in a nucleus...

True, except that it is not me who wants to make that definition. While, I admit that there is no absolute consensus of how to define x- and gamma rays, one of the most used ways is exactly that.

What about the photons released by the mutual annihilation of electron-positron pairs? Non-nuclear, yet definitely gamma rays...

Cleverly put trap, you almost got me on that one. But strictly speaking that radiation has its own name (annihilation radiation/photons). But yes, I am prepared to accept those (and similar) as (annihilation) gamma in casual language.

On the other hand, what about the characteristic radiation coming from the K-shell of (say) a bismuth-214 atom, after the decay of led-214? It has energies ranging from 75-90 keV, which is roughly twice the cutoff you suggested, but they are surely still x-rays... At the same time the decay releases real gammas with a lower energy, than these x-rays.

Some gamma rays emitted by nuclear processes are actually way down in the UV range. On the other hand, some X-ray emitters can produce photons far more energetic than any photon emitted by nuclear decay. Also, the lower case gamma (γ) is used as shorthand for all photons in Feynman diagrams and elsewhere. In astronomy, however, all photons above a certain energy (roughly into the MeV range) are classed as gamma rays - mainly because their origin is uncertain.

So, like I said, fucked up terminology! It makes much more sense to me to classify photons based on energy rather than source. But will they listen?

[mistermack]

http://www.bbc.co.uk/news/science-environment-30491840

Pretty much every thunderstorm produces a burst of gamma radiation. So why aren't there more Hulks about? Answer that one, Darwin!

Because technically those are X-rays, not gamma. If they are called gamma-ray bursts, that would be because astronomers still confuse the two, by referring to fenomena that produce highly energetic X-rays, for gammabursts. I see no reason, why this confusion should be brought back here to planet earth.

And no-one has ever seen a Hulk produced by mere X-rays

If they have a frequency above 1019 Hz, then they are gamma rays, whatever their source...

Maybe back when you went to school, but not anymore . Distingushing gamma and x-rays by source is the only sane way to distinguish them, as dividing them by frequency is completely arbitrary. But I do agree, that we would need a word for high energy photons, that would cover both.

What does it matter the source? Electromagnetic radiation is electromagnetic radiation. One photon differs from another only in wavelength/frequency/energy. Where they come from is irrelevant.

Except for entangled pairs.
Something unique about them, which other seemingly identical particles haven't got ?

[Xamonas Chegwé]

Except for entangled pairs.
Something unique about them, which other seemingly identical particles haven't got ?

Interesting point. I suppose the answer is that that uniqueness is present only when the two particles are considered as a system. Individually they are identical to any other particle. There is no measurement you can take of a single particle that will reveal its entangled nature.

[Xamonas Chegwé]

And, of course, there is no difference between entangled photons of 10MeV produced by a nuclear event and a pair produced otherwise.

[MiM]

And, of course, there is no difference between entangled photons of 10MeV produced by a nuclear event and a pair produced otherwise.

Which is why they have a common name "photons". What is your problem?

[mistermack]

You must be able to demonstrate entanglement, because it's been measured that the entangled pair changes instantly, to a very high degree of accuracy, as compared to the finite time that the speed of light would have taken. According to wiki.
But what I gather is that you can't do it live in real time. You can only demonstrate AFTERWARDS that it did happen, and happen instantly, as far as we can measure it.
So you can't pass a message that way faster than light, but you can demonstrate that particles are entangled.
The particles must be unique, because if you alter the spin of an entangled particle, the ONLY particle that is affected by that is it's pair. Other particles, that seem to be identical, can't be, because they aren't affected.

I think I read somewhere that every particle that exists might have an entangled pair particle somewhere in the Universe. To conserve the overall angular momentum etc of the universe to zero.
I have no idea if I'm remembering that right though.

[pErvinalia]

And, of course, there is no difference between entangled photons of 10MeV produced by a nuclear event and a pair produced otherwise.

Which is why they have a common name "photons". What is your problem?

He hasn't been wanking enough lately..

[Xamonas Chegwé]

And, of course, there is no difference between entangled photons of 10MeV produced by a nuclear event and a pair produced otherwise.

Which is why they have a common name "photons". What is your problem?

I don't have a problem. Except for the fact that every other name for a type of photon: radio wave, IR, UV, visible light, etc. refers to a specific range of frequencies. That gamma rays and x-rays don't (except to astronomers!) is kinda perverse.

[Xamonas Chegwé]

You must be able to demonstrate entanglement, because it's been measured that the entangled pair changes instantly, to a very high degree of accuracy, as compared to the finite time that the speed of light would have taken. According to wiki.
But what I gather is that you can't do it live in real time. You can only demonstrate AFTERWARDS that it did happen, and happen instantly, as far as we can measure it.
So you can't pass a message that way faster than light, but you can demonstrate that particles are entangled.
The particles must be unique, because if you alter the spin of an entangled particle, the ONLY particle that is affected by that is it's pair. Other particles, that seem to be identical, can't be, because they aren't affected.

I think I read somewhere that every particle that exists might have an entangled pair particle somewhere in the Universe. To conserve the overall angular momentum etc of the universe to zero.
I have no idea if I'm remembering that right though.

So, if every particle in the universe is entangled with another particle, there is certainly nothing special about entangled particles!

[laklak]

You can make torpedoes out of protons.

[JimC]

You can make torpedoes out of protons.

Are you positive about that?

[mistermack]

I find entanglement really fascinating.

I think it's big evidence for a fifth dimension, as it's effects exceed the limits on matter and energy in the four dimensions that we experience.

So in a way, photons can be identical in the four dimensions that we know. But all bets are off for other dimensions.

[Xamonas Chegwé]

I find entanglement really fascinating.

I think it's big evidence for a fifth dimension, as it's effects exceed the limits on matter and energy in the four dimensions that we experience.

So in a way, photons can be identical in the four dimensions that we know. But all bets are off for other dimensions.

Personally, I find entanglement to be suggestive of the de Broglie-Bohm theory. Basically that particles do have definite position and momentum at all times but that those properties are guided probabilistically by a wavefunction pilot-wave and thus cannot be predicted from initial conditions.

[mistermack]

Personally, I find entanglement to be suggestive of the de Broglie-Bohm theory. Basically that particles do have definite position and momentum at all times but that those properties are guided probabilistically by a wavefunction pilot-wave and thus cannot be predicted from initial conditions.

That's quite interesting, although a lot of it is over the top of my head on first reading.
One thing I did find interesting though, was

The theory is deterministic.[1] Most (but not all) variants of the theory that support special relativity require a preferred frame.

I've always felt that even though relativity works for any frame, that there probably is a preferred frame.
But whenever I mentioned the possibility, I got howls of derision. Usually from people who know very little, but manage to absorb that one headline fact, that there is no preferred frame in relativity.

[Xamonas Chegwé]

I'm not saying that Bohm interpretation is right. But entanglement does lend it credence. Apparently, it is gaining weight again at the moment after decades of dismissal. I suspect that the "truth" is somewhat weirder though. And I don't hold with a preferred frame - simply because the maths don't require one. Doesn't mean that there isn't one. But why add a flying, purple elephant to your equations if they work fine without it?