Don't understand death by entropy

[atharh]

I'm catching up with the Wonders of the Universe episodes and in the first one Brian Cox mentioned that after a gazillion years the Universe's entropy will increase and eventually turn into a sea of photons.

How can that be? I didn't think atoms would disintegrate to photons.

Did I miss something in my physics class?

[ajg]

Proton decay

Only theoretical, and depends on the LHC finding the Higgs Boson - if it doesn't, we have to chuck a fair bit of the standard model of particle physics out and go back to the drawing board, although I don't pretend to understand this to any depth ...

[brianb]

I didn't think atoms would disintegrate to photons.

This is controversial & depends on some features of particle physics which are utterly lacking in experimental verification. But it is thought that all particles are fundamentally unstable and will eventually decay, unless they happen to be travelling at the speed of light (in which case the aging process is suspended by application of Lorenzian time dilation). When a particle decays it gives rise to a collection of other particles (possibly none of them) and photons, the other particles are of course subject to decay themselves, so everything eventually degrades to photons - which travel at the speed of light and therefore don't decay.

I don't fully understand the theory of particle decay but I believe it is intimately concerned with the weak nuclear force, which also controls the radioactive decay process in atomic nuclei.

[Catanonia]

harder to think about is how black holes can seep matter via the uncertainty principle or quantum tunnelling.

Basically an atom can pass through a physical barrier such as the event horizon of a black hole. But the chances are 1 in something like 1 billion years.

How long would it take a black hole to loose all of it's atoms / electrons / protons etc via this process. Too big a number for me to think about.

This is what B Cox was on about about the true potential age of the universe and our insignificant time scale on it. Staggering numbers.

[mikeknowle]

harder to think about is how black holes can seep matter via the uncertainty principle or quantum tunnelling.

...so all black holes eventually lose all their mass by 'evaporation'!

[Catanonia]

...so all black holes eventually lose all their mass by 'evaporation'!

Yes : according to Mr Hawkings. (I think I got this correct)

[Byz1453]

Quite so, it's called Hawking Radiation and is proportional to the inverse square of the black hole's mass, eventually it accelerates and ends with an explosion of elementary particles. apparently...

All the Hydrogen goes when the universe is about 10^16 years old and the large black holes will take 10^100 years to evaporate and that'll be that!

Allegedly...

So I'm told...

Maybe...

What do I know, I sell beer for a living...

[mikeknowle]

Ah thought so!

So after that, it's time to conduct a brownian motion experiment - i.e. put the kettle on...

[atharh]

On the show he made it seem like Proton Decay was a done deal.

Great show though, really enjoying learning new things.

But I wish he would stop posing. That sequence of him gangling along trying to look butch while the building behind him exploded had me in stitches.

[Catanonia]

Quite so, it's called Hawking Radiation and is proportional to the inverse square of the black hole's mass, eventually it accelerates and ends with an explosion of elementary particles. apparently...

ahhh, ok got it, so explains how it would happen. Exponential growth. Not such big numbers anymore (ish)

[brianb]

an atom can pass through a physical barrier such as the event horizon of a black hole.

That's not quite right ... we're talking fundamental particles rather than atoms.

Now, the "quantum foam" which exists at very small scales means that pairs of particles and antiparticles are continually coming into existence and almost immediately annihilating each other - the energy from the annihilation exactly balances that needed to produce the particle-antiparticle pair in the first place, so that on a large scale everything balances itself out. (There was an excellent explanation of this in the programme "Nothing" broadcast on BBC4 last night.)

Unless there is an event horizon nearby.

Then what happens is that there is a small chance that one of the particle/anti-particle pair will find itself on the other side of the event horizon to its counterpart, so annihilation cannot occur. Though it is still at the bottom of a very deep gravitational well, the sides are no longer vertical, so there is a chance that it can escape from the system. Obviously the more massive the black hole is, the greater the energy needed to escape. But a massive black hole also has a bigger event horizon ... Do the sums and it turns out that the evaporation rate is inversely proportional to the fourth power of the mass of the black hole (i.e. a hole twice as massive takes 16 times as long to evaporate).

This is all a bit strange, as the particle that escapes carries energy from the black hole the black hole's mass must decrease, even though it's apparently gained the mass of the particle that didn't escape ... however intuition doesn't count for much in quantum mechanics!