Can Matter be Created or Destroyed?

[Cyberman]

Isn't there an energy loss from any system once the available energy has been converted to heat? Or am I barking up the wrong trousers?

[Alex K]

Isn't there an energy loss from any system once the available energy has been converted to heat? Or am I barking up the wrong trousers?

I'm not sure why you say there is energy loss. The heat you produce e.g. via friction is simply the kinetic energy of the atoms. But because their movement is random, it represents a high entropy and cannot by itself be reused to do work.

[Rhondazvous]

I've read that the device used to produce particle pairs is called a particle collider. this is a type of particle accelerator. You need at least 2 photons that do something in the vicinity of a heavy atomic nucleus, such as lead or gold.

What I'm trying to find is exactly what the photons do in the process of conversion to an electron-positron pair, and what is their relationship to the nucleus. Do they collide with the nucleus or with each other?

[Cyberman]

Isn't there an energy loss from any system once the available energy has been converted to heat? Or am I barking up the wrong trousers?

I'm not sure why you say there is energy loss. The heat you produce e.g. via friction is simply the kinetic energy of the atoms. But because their movement is random, it represents a high entropy and cannot by itself be reused to do work.

I was referring to the heat energy lost after the useful work in a system. The reason why perpetual motion is impossible. I'm sure I've mangled it horribly.

[Alex K]

I've read that the device used to produce particle pairs is called a particle collider. this is a type of particle accelerator. You need at least 2 photons that do something in the vicinity of a heavy atomic nucleus, such as  lead or gold.

What I'm trying to find is exactly what the photons do in the process of conversion to an electron-positron pair, and what is their relationship to the nucleus. Do they collide with the nucleus or with each other?

Yes, pair creation happens all the time at colliders such as the Large Hadron Collider (you do know my LHC thread, right?

http://atheistforums.org/thread-33518.html
)
If you want to know what photons do in pair creation, it is useful to look at the corresponding feynman graphs.



Basically, according to current understanding, the photons exchange a virtual electron and this results in an electron and a positron to be created. Quantum electrodynamics simply postulates the interactions between the electron/positron and photon fields, no deeper underlying mechanism of interaction between them is known. In superstring theory, which is speculative, various models give a more detailed account how the conversion happens - such as end points of strings changing from one higher dimensional "brane" to another and thus changing the particle type.

Anyways, the nucleus in such experiments usually merely provides a counter mass which can absorb/emit a photon for the process. The precise details of the nucleus are usually unimportant, what you need is some massive thing with an electric charge.

[Rhondazvous]

Yes, pair creation happens all the time at colliders such as the Large Hadron Collider (you do know my LHC thread, right?

http://atheistforums.org/thread-33518.html
)
If you want to know what photons do in pair creation, it is useful to look at the corresponding feynman graphs.



Basically, according to current understanding,  the photons exchange a virtual electron and this results in an electron and a positron to be created. Quantum electrodynamics simply postulates the interactions between the electron/positron and photon fields, no deeper underlying mechanism of interaction between them is known. In superstring theory, which is speculative, various models give a more detailed account how the conversion happens - such as end points of strings changing from one higher dimensional "brane" to another and thus changing the particle type.

Anyways, the nucleus in such experiments usually merely provides a counter mass which can absorb/emit a photon for the process. The precise details of the nucleus are usually unimportant, what you need is some massive thing with an electric charge.

Wow! That does explain a lot. I'm looking at the graph. The photons go in and come out as e+ and e-. Is the nucleus right there in the center where the photons meet (please correct me if they don't actually meet but just come close when they exchange the virtual electron)? Is the virtual electron taken from the nucleus?

No, I did not know about your LHC thread. I knew you were very knowledgeable about things quantum, but had no idea you were dealing specifically with pair production. My plot calls for the production of positrons specifically. So that would be more like the VEPP 2000 than the LHC. Still, this calls for a big acknowledgement in the final publication.

[Edwardo Piet]

My guess is:

Matter can be created, and it was created during the "Big Bang." I also believe that a reversal of the process, in theory, would be an example of matter being destroyed. Whether that is possible in practice perhaps depends on whether the Big Crunch will ever happen. According to Lawrence Krauss it will not, the Universe will keep expanding forever and ever.
ou
So I would say I reckon matter can be created, but not destroyed - assuming Lawrence Krauss is right.

Energy however, I believe is eternal. Something must have always existed because it doesn't make sense for "nothing" to exist. It is possible for "empty space" to exist, but that is actually something, just barely. It exists as something at least on the subatomic level. And that is where the title of the book "A Universe From Nothing" by Lawrence Kraus is a misnomer (It should really be called "A Universe From "Empty space" Which Is Almost Nothing But Actually Just Barely Something At least On The Subatomic Level." - but that wouldn't be a very catchy title now would it? ). Although the science itself I am sure is very accurate.

Energy cannot be created or destroyed. Matter can be created, and may or may not be able to be destroyed.

Just my 2 cents/pence.

[Alex K]

My guess is:

Matter can be created, and it was created during the "Big Bang." I also believe that a reversal of the process, in theory, would be an example of matter being destroyed.

You are talking about the dreaded Gnab Gib here, right...

Whether that is possible in practice perhaps depends on whether the Big Crunch will ever happen. According to Lawrence Krauss it will not, the Universe will keep expanding forever and ever.

According to almost everyone else as well. It's not so much about Lawrence Krauss' opinion, he simply recounts the current scientific consensus here. The crucial issue is about the nature of Dark Energy. If the observed Dark Energy simply takes the form of Einstein's cosmological constant, it always remains the same, as the term "constant" implies. If it remains the same in magnitude, forever it will dominate our destiny - as everything else gets diluted down by the expansion, the cosmo constant prevails unchanged, driving our universe towards eternal exponential expansion. Noone can currently know (for lack of empirical evidence) whether Dark Energy truly is this simplest of all versions or something more complicated, but Occam's razor would suggest that if there is such a trivially simple explanation for the data, we should consider it likely.

ou
So I would say I reckon matter can be created, but not destroyed - assuming Lawrence Krauss is right.

If you like you should read an article on inflation and reheating, to get an idea how matter might have been created from a different form of energy.

Energy however, I believe is eternal. Something must have always existed because it doesn't make sense for "nothing" to exist.

How do you define energy?

It is possible for "empty space" to exist, but that is actually something, just barely. It exists as something at least on the subatomic level. And that is where the title of the book "A Universe From Nothing" by Lawrence Kraus is a misnomer (It should really be called "A Universe From "Empty space"  Which Is Almost Nothing But Actually Just Barely Something At least On The Subatomic Level." - but that wouldn't be a very catchy title now would it? ). Although the science itself I am sure is very accurate.

Yes, I think the name is unfortunate, but if you want to sell, you need something catchy, and this stuff is something publishers love.

Energy cannot be created or destroyed. Matter can be created, and may or may not be able to be destroyed.

Why the distinction between matter and energy here? When you say matter cannot be destroyed, do you mean baryonic matter remains because of baryon number conservation?

[Rhondazvous]

Yes, pair creation happens all the time at colliders such as the Large Hadron Collider (you do know my LHC thread, right?

http://atheistforums.org/thread-33518.html
)
If you want to know what photons do in pair creation, it is useful to look at the corresponding feynman graphs.



Basically, according to current understanding,  the photons exchange a virtual electron and this results in an electron and a positron to be created. Quantum electrodynamics simply postulates the interactions between the electron/positron and photon fields, no deeper underlying mechanism of interaction between them is known. In superstring theory, which is speculative, various models give a more detailed account how the conversion happens - such as end points of strings changing from one higher dimensional "brane" to another and thus changing the particle type.

Anyways, the nucleus in such experiments usually merely provides a counter mass which can absorb/emit a photon for the process. The precise details of the nucleus are usually unimportant, what you need is some massive thing with an electric charge.

Wow! That does explain a lot. I'm looking at the graph. The photons go in and come out as e+ and e-. Is the nucleus right there in the center where the photons meet (please correct me if they don't actually meet but just come close when they exchange the virtual electron)? Is the virtual electron taken from the nucleus?

No, I did not know about your LHC thread. I knew you were very knowledgeable about things quantum, but had no idea you were dealing specifically with pair production. My plot calls for the production of positrons specifically. So that would be more like the VEPP 2000 than the LHC. Still, this calls for a big acknowledgement in the final publication.

Quantum, I think these last questions may have slipped by.

[Alex K]

Oh yes it did!

No, the nucleus is the source of one of the photons. You would draw it as an X at its end or as a thick line running parallel all the way from left to right