JamesR mentioned today in another thread that according to relativity matter/energy can be created and destroyed. One of the first things we covered in physics (only done a little) was that this can't happen. Can some of you expand on this please?

i thought energy\matter could only change shape and be redistrabuted not created and destroyed

Originally posted by Adam
JamesR mentioned today in another thread that according to relativity matter/energy can be created and destroyed. One of the first things we covered in physics (only done a little) was that this can't happen. Can some of you expand on this please?

yes, if you read about the CERN (http://livefromcern.web.cern.ch/livefromcern/antimatter/) and its anti-matter projects. When matter and anti-matter collide they literally destroy each other.

What happens? Matter is destroyed?

Well...destroyed into pure energy.

Keeping in mind E=mc^2 (so energy=matter)

Without a complete theory of quantum gravity, it's hard to tell where matter exactly came from (probably pure energy from the Big Bang cooled and formed into "matter"). Maybe Thed or James R can help me here. But Hawking, Turok, and some other scientists, believe the Universe at the Planck Era (?) with all the energy in it could have possibly been generated by an instanton (a solution of Metric Path Integrals). The instanton itself came to exist from literllay nothing (no I still don't believe "nothing ---> something"). After the Planck Era, the energy of the young universe was dominated by a scalar field called an inflation field. This inflation generated a potential energy V inflaton, I think. Then time passes leaving the inflation field at a local minimum and as the inflation rolls down to a new minimum, the excess energy is transformed into particles (matter!) that would later form into baryons, leptons, quarks, and so on. But at the same time the universe expanded exponentially and this is basically the inflationary picture for the "creation" of matter. Then, mass and energy are conserved after this occurs by Einstein's general relativity.

Correct me if I'm wrong. ;)

Um, I suppose so. Theoretically, you can convert mass into energy right? Then the mass has disappeared. You just have more energy.

Also, mass can spontaneously fade away from the universe. Things such as car keys, credit cards, wallets, coins etc come to mind...lol behold the theory that must kneel in the face of empirical evidence!!! Mass can spontaneously disappear!!

There is no god, afterlife or divine love. There is only Entropy, the mother from which we were all born. She tugs our souls with the beautiful, maternal love of chaos. Why do you keep Her waiting?Zero, the same entropy you praise will one day end our universe;) tht's why I'm not a follower of it and sacriface no virgins also.

Let me be clear about this. I said that <b>matter</b> can be created and destroyed, but not energy.

According to E=mc² and related equations, matter and energy can be converted from one to another. We see matter converted to energy (in the form of light) in matter-antimatter anihilation. We see energy converted into matter in high-energy particle accelerator collisions (to take one example).

One of the fundamental laws of physics is that the net amount of mass and energy in the universe is constant.

Nachos grassy-arse. :)

Originally posted by Adam
Nachos grassy-arse. :)

Does that post give you an idea of how much I know about the Big Bang or what?

I don't wish to prove myself to anyone Adam. But if you saying thanks to me and everyone else, no problem.

I'm just stressing the non existence of any god whatsoever.

Anyhow, the thing about the net energy/mass being constant is being challenged (though feebly) by the thing that Hawking discovered. He found that, for no reason at all, an electron and a positron (anti matter electron, has positive charge) will pop into existence in space, and that the positron gets sucked into a black hole and be converted into radiation called 'Hawking radiation'. I strongly doubt if Hawking got his stuff right, but if he did this would be interesting.

Any thoughts?

Hi Zero,

The energy for the creation of the electron/positron pair is taken from the black hole's gravitational energy. Hence this is an example of how energy can "condense" to form matter. The total amount of energy = matter remains preserved in the universe.

Bye!

Crisp

But where did the initial electron and positron come from, if it appeared out of no reason at all, and no energy was consumed in their creation? That is the point here.

Zero,

The spontaneous creation and annihilation of particles is a feature of quantum field theories. Hawking did not invent this; he just applied it to black holes. Due to the uncertainty principle, energy can be temporarily "borrowed" from the vacuum to create particles out of nothing. However, the principle requires that the borrowed energy must be "paid back" in a short time, so usually the particles immediately annihilate each other. In the case of Hawking radiation, the energy debt is repaid by the black hole, so a real particle can be created. Energy conservation is violated for a short time (allowed by the uncertainty principle), but in the end everything balances up again.

If you don't mind my asking James, where do you work for a living? You seem to know an aweful lot about physics, I'm interested in becoming a physicist myself and I'm looking at the different job routes I could choose from. I would like to do research into either nanotechnology, theoretical physics, quantum physics or M-Theory. So far the only jobs I have found related to the latter 3 are in universities, but I don't particularly want to teach classes. Any help would be appreciated.

Originally posted by Xelios
If you don't mind my asking James, where do you work for a living? You seem to know an aweful lot about physics.

Yes, I'm curious also James R, Thed, and (Q).

All of them are intelligent and have an abundance of knowledge concerning science. :)

Originally posted by James R
Zero,

The spontaneous creation and annihilation of particles is a feature of quantum field theories. Hawking did not invent this; he just applied it to black holes. Due to the uncertainty principle, energy can be temporarily "borrowed" from the vacuum to create particles out of nothing. However, the principle requires that the borrowed energy must be "paid back" in a short time, so usually the particles immediately annihilate each other. In the case of Hawking radiation, the energy debt is repaid by the black hole, so a real particle can be created. Energy conservation is violated for a short time (allowed by the uncertainty principle), but in the end everything balances up again.

Thanks very much James, this is precisely what I was after.

"The spontaneous creation and annihilation of particles is a feature of quantum field theories. Hawking did not invent this; he just applied it to black holes. Due to the uncertainty principle, energy can be temporarily "borrowed" from the vacuum to create particles out of nothing. However, the principle requires that the borrowed energy must be "paid back" in a short time, so usually the particles immediately annihilate each other. In the case of Hawking radiation, the energy debt is repaid by the black hole, so a real particle can be created. Energy conservation is violated for a short time (allowed by the uncertainty principle), but in the end everything balances up again. "

Isn't this what causes black holes to shrink with time?

What I never understood was why this radiation is emitted more the smaller a black hole gets. I've read that smaller black holes have a higher "temperature" than larger ones (by measure of the Hawking radiation given off), why is this?

Xelios:

<i>Isn't this what causes black holes to shrink with time?</i>

Yes.

<i>What I never understood was why this radiation is emitted more the smaller a black hole gets. I've read that smaller black holes have a higher "temperature" than larger ones (by measure of the Hawking radiation given off), why is this?</i>

This is correct. I'm not sure exactly why that happens.

My quess is that they are more concentrated. What a blackhole is emiting isn't from his own mass. The emition comes because it "heated" the particles that are in it's affection zone but do not belong to it. When it is hotter the particles move faster. When it becomes smaller maybe it's concentration is increasing, thus the "heat" grows and particles are moving ever faster, resulting in greater emision. Larger black holes maybe have the same mass, but it is over a greater surface.

Hawking radiation must depend on gravity because nothing gets beyond the Schwarzschild radius except gravitation. Virtual photons, which originate at the Schwarzschild radius and move at the speed of light, are changing their frequencies or energies as they gain kinetic energy from being accelerated by the gravity of the black hole, which is proportional to the mass and the distance on which it is accelerated.

As the distance of the Schwarzxchild radius decreases, the kinetic energy increases as the virtual photons experience an increase in gravitation. Their energies or frequencies increase and thus they draw more energy from a smaller black hole then a larger one.