Energy into matter becomes...?

[Baby Astronaut]

If you convert energy into matter, what does it become exactly? Complete atoms, or a whole bunch of randomly loose subatomic particles?

Edited June 22, 2009 by swansont
deleted section at user request; moved from GD

[Severian]

The entire phrase "convert energy into matter" is at worst wrong and at best misleading. In actuality you are just converting energy from one form into another.

 

For example, consider the creation of an electron together with its antiparticle, a positron. Firstly, there has to be something there beforehand, carrying the energy. In this case, it is a photon, which disappears when the electron-positron pair are created. The kinetic energy of the photon (basically all its energy) is then converted into a combination of mass energy (since both the electron and positron have mass) and kinetic energy of the particle antiparticle pair (whatever is left over).

[swansont]

If you convert energy into matter, what does it become exactly? Complete atoms, or a whole bunch of randomly loose subatomic particles?

 

In general, particle/antiparticle pairs. Not a random assortment or Whitman sampler.

[proton]

If you convert energy into matter, what does it become exactly? Complete atoms, or a whole bunch of randomly loose subatomic particles?

To be precise, one doesn't convert energy into matter. One converts radiation into matter. What happens is that the form of energy changes.

 

An example would be pair production. In nuclear physics this occurs when a photon is in the vicinity of a nucleus, otherwise momentum wouldn't be conserved. The photon goes into the reaction and an electron/positron pair come out of the reaction. The energy remains the same. Only the form of the energy changes.

 

oops! I see Severian beat me to it. Sorry!

[swansont]

To be precise, one doesn't convert energy into matter. One converts radiation into matter. What happens is that the form of energy changes.

 

But the energy need not be radiation. You can convert kinetic energy, too, as occurs in any particle collider.

[proton]

But the energy need not be radiation. You can convert kinetic energy, too, as occurs in any particle collider.

Yes. That is quite correct. My point was that the conversion pertains to a conversion of the form of radiation from one form to another. I used radiation as an example and neglected to elaborate. Thanks for correcting me.

 

Laymen have the tendancy to think of light as being "pure energy" and that was something I was trying to steer readers away from.

[Baby Astronaut]

Yes. That is quite correct. My point was that the conversion pertains to a conversion of the form of radiation from one form to another. I used radiation as an example and neglected to elaborate. Thanks for correcting me.

 

Laymen have the tendancy to think of light as being "pure energy" and that was something I was trying to steer readers away from.

Thanks proton, your answers were indeed helpful. I totally didn't notice my using "energy" to describe a type of energy

 

That said, now I'm wondering a couple more things.

 

1. When something is converted into matter, does it always form in pairs only? If not, what are the other possibilities?

 

2. Is there such a thing as "pure energy" (or something close to it)?

[proton]

1. When something is converted into matter, does it always form in pairs only? If not, what are the other possibilities?

It depebds on what you call matter. In an article written by Einstein where he published a review article on his general theory of relativity he referred to matter as anything for which the stress-energy-momentum tensor is not zero. In layman's terms one can say that Einstein defined matter as anything which has energy. Thus Einstein would have considered an electric field to be a form of matter. Typically one is describing changes in the form of matter from one from to another. Thus if you have a particle annihilating its antiparticle then energy in the form of proper energy + kinetic energy is changed to electromagnetic energy.

 

Always remember that no matter what, the energy before a reaction equals the energy after a reaction.

 

When you asked does it always form in pairs only you must have swansont's comment in mind. I don't know why he said that. Perhaps he was thinking only of pair production in which case that's true. But the idea of conversion has to do with a change in the form of energy taking place and can happen in other circumstances such as nuclear fission in which case the comment about pairs being produced does not apply.

2. Is there such a thing as "pure energy" (or something close to it)?

Only on TV and in the movies.

 

When people use the term "pure energy" they tend to be referring to matter for which there is no proper mass (aka rest mass).

Edited June 26, 2009 by proton

[swansont]

When you asked does it always form in pairs only you must have swansont's comment in mind. I don't know why he said that. Perhaps he was thinking only of pair production in which case that's true. But the idea of conversion has to do with a change in the form of energy taking place and can happen in other circumstances such as nuclear fission in which case the comment about pairs being produced does not apply.

 

Is matter created in fission? Same number of neutrons, protons and electrons before and after.

[Severian]

It depebds on what you call matter.

 

The more modern definition of matter is quarks and leptons. In this case, the answer to his question would be: yes - they are always created in pairs in order to conserve quark or lepton number (which are symmetries of the SM).

[proton]

Is matter created in fission? Same number of neutrons, protons and electrons before and after.

As I said, it depends on how you define the term "matter". When you asked that question you already had a definition in mind as far as what it means for something to be matter. When fission occurs there is a change from rest mass energy to kinetic energy (where radiation having all kinetic energy).

 

As far as a "modern" definition goes, there really is none. Different physicists mean different things by it. It's really a vauge term which is either ill-defined or highly avoided. Sure, you can find a text here and there which attempts define the term but its always a bit vauge. Not really solid enough to determine qauntitatively and even then different texts define it diffferently or avoid the term altogether.

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The more modern definition of matter ..

I seriosuly doubt that in that most, if not all, physicists prefer to avoid that term when at all possible. but if you believe differently then p\Please post a reference to a modern textbook which provides such a definition. Preferably a few so that we can see if they all agree.

 

Wikipedia attempts to define it here - http://en.wikipedia.org/wiki/Matter

 

Typically the definition alludes to mass, which of course differs from one person to another. The definition says that matter is what has mass and occupies space. Does a point particle occupy space?

 

Notice the comment in the link

In the realm of cosmology, extensions of the term matter are invoked to include dark matter and dark energy,..

Dark energy is characterized as having negative pressure which results in a negative active gravitational mass. Thus pressure is in a sense a form of matter.

 

Have you looked at Taylor and Wheeler's SR text? They address the term "amount of matter" commenting that history has struck down every attempt to define such a term. They mentioned this when they addressed the question as far as whether mass is a measure of "amount of matter".

 

It's for these reasons that I choose not to accept any definition as being universally accepted. But once you choose a definition and explain how to quantify it we can talk about it if you'd like.

Edited June 27, 2009 by proton
Consecutive posts merged.

[Baby Astronaut]

As I said, it depends on how you define the term "matter".

As far as a "modern" definition goes, there really is none. Different physicists mean different things by it. It's really a vauge term which is either ill-defined or highly avoided.

Perhaps we can solve this by defining what non-matter energy is.

 

As I see it, non-matter energy is continually a wave. Matter also possibly vibrates continually, unless I'm wrong (on both counts).

[proton]

Perhaps we can solve this by defining what non-matter energy is.

 

As I see it, non-matter energy is continually a wave. Matter also possibly vibrates continually, unless I'm wrong (on both counts).

I'm not sure what you're seeking? If you're looking for a definition of the term matter then I don't think I can be of any help for the reasons I mentioned above. Is it really that important? I'd say that it's more important to understand what people mean by it when they use it. Thus if you see someone use the term then you'd be better off asking them what they mean by it. For example; when you heard the term "convert matter to energy" it referred to changing proper mass to kinetic energy.

 

In quantum mechanics there is a wavelength associated with every particle so I don't see how you can't resolve it in that way.

[Baby Astronaut]

I meant solving the inability to define matter, as I happen to think everything is definable. Just not always easily (or currently) but, ultimately definable.

 

For example; when you heard the term "convert matter to energy" it referred to changing proper mass to kinetic energy.

Oddly, I had assumed non-matter energy to just automatically have a flow with no kinetic energy involved. So to understand you, photons or massless things are simply kinetic energy. If so...how very counter-intuitive, seeing as objects can gain or lose kinetic energy just by switching reference frames.

 

I guess a photon moving alongside something traveling at c has no kinetic energy and therefore would be virtually nonexistent....except for a tiny bit (I just now learned about invariant mass). But in other reference frames, the photon is whole again.

 

Boggles the mind. Is someone able to explain this? Or did I get it all wrong?

[proton]

I meant solving the inability to define matter, as I happen to think everything is definable. Just not always easily (or currently) but, ultimately definable.

I'm not suggesting that the term matter cannot be defined. It's easy to define terms. What is not so easy is to define a term for which the definition is not problematic. For example; suppose we define the term "matter" as "that which has non-zero proper mass". What then of a two photon system for which the proper mass of the system is non-zero? That would mean that one photon is not matter, a system of two photons moving in the same direction is not matter but a system of two photons moving in opposite directions is matter. What of systems for which all we have is the stress-energy-momentum tensor. In that case all we know is what the energy density, stress and momentum density is. We don't know what the system is comprised of. Should we be able to quantize the quantity of matter in that case? What is we say that anything composed of particles which has zero proper mass is not matter. Would you object to the consequence of non-matter being able to generate a gravitational field? Recall that the physicist John Wheeler said "Matter tells space how to curve, and space tells matter how to move." This would no longer be true if that was the case.

Oddly, I had assumed non-matter energy to just automatically have a flow with no kinetic energy involved. So to understand you, photons or massless things are simply kinetic energy.

No. They have kinetic energy. One does not say that they "are" kinetic energy. Kinetic energy, like mass and charge, is a property.

If so...how very counter-intuitive, seeing as objects can gain or lose kinetic energy just by switching reference frames.

Yep. The energy of anything is frame dependant.

I guess a photon moving alongside something traveling at c has no kinetic energy ...

Special relativity dictates that such a thing is impossible. I.e. it is impossible for a photon to be a rest.

 

Do you have access to a library? If so then you might like to read the following article

 

Does nature convert mass to energy?, Ralph Baierlein, Am. J. Phys. 75(4), April 2007

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I just found and interesting quite in Physics for Engineers and Scientists - Third Ed. Vol. II by Ohanian and Markert, page 722

Fields are a form of matter - they are endowed with energy and momentum ..., and therefore they exist in a material sense.

Similarly in Classical Electrodynamics - Second Edition, Hans C. Ohanian, page 50

As we shall see later, fields have energy. They therefore are a form of matter, and they can be regarded as the fifth state of matter (solid, liquid, gas and plasma are the other four states of matter).

Note: Others refer to the Bose-Einstein condensate as the fifth state of matter.

Edited June 28, 2009 by proton
Consecutive posts merged.

[swansont]

I just found and interesting quite in Physics for Engineers and Scientists - Third Ed. Vol. II by Ohanian and Markert, page 722

 

Similarly in Classical Electrodynamics - Second Edition, Hans C. Ohanian, page 50

 

It's the same author, so these are not two independent instances, and besides that, it doesn't matter (as it were). A handful of people using a particular terminology does not make it the standard.

[proton]

It's the same author, ..

Yes. It appeared in two different texts. One of basic physics and one on EM. That's why I posted them both. And since the author is the same it was obvioius that they were not independent instances so I didn't see the point in mentioning that point.

A handful of people using a particular terminology does not make it the standard.

Nobody suggested it was standard, certainly not I.

[swansont]

Yes. It appeared in two different texts. One of basic physics and one on EM. That's why I posted them both. And since the author is the same it was obvioius that they were not independent instances so I didn't see the point in mentioning that point.

 

But you found it worth mentioning both texts.

 

Nobody suggested it was standard, certainly not I.

 

Then what's the point?

[proton]

But you found it worth mentioning both texts.

So what? Why do you make such a big deal of it. I found the first reference by searching online and then copied it from my copy. After that I looked in the author's EM book which I have so I then added it. I didn't realize that adding it would confuse you so much, especially since the author's are the same. Actually the first instance makes it clear that both authors agree with the usage and that the second usage is found in a more advanced text on the subject.

Then what's the point?

It's obvious what my point was. To demonstrate that such an interpretation, e.g. that of Einstein's, is found in modern physics texts. Edited June 28, 2009 by proton

[Severian]

I seriosuly doubt that in that most, if not all, physicists prefer to avoid that term when at all possible. but if you believe differently then p\Please post a reference to a modern textbook which provides such a definition. Preferably a few so that we can see if they all agree.

 

Is the Particle Adventure good enough for you?

 

"All the known matter particles are composites of quarks and leptons"

"Quarks are one type of matter particle... The other type of matter particles are the leptons."

 

Admittedly, the particle adventure is aimed at a rather low level. Maybe you would prefer Fermilab's public understanding site?

 

"Physicists have identified 12 building blocks that are the fundamental constituents of matter. Our everyday world is made of just three of these building blocks: the up quark, the down quark and the electron."

 

I am at home at the moment, away from my text books, but I wil give you a list of text books tomorrow (if I can be bothered).

[proton]

Is the Particle Adventure good enough for you?

No. First off its not a modern textbook. In the second place I don't know who wrote it and in the third place it doesn't even provide a definition. The person who wrote that web page is clearly using the term in a vauge sense, as most people do. Notice that he only said

All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles.

I even agree with that statement. That doesn't mean I know what the author has in mind for a definition. Notice that he didn't refer to electrons? What are we to conclude as to whether an electron is made of matter?

 

My point is that different people use this term in different ways. It's not a term which requires a technical definition. Nobody ever really needs to use such a term in fact.

 

Consider the context in which it is used too. How would you determine whether something was matter by examining the stress-energy-momentum tensor? For example; if there is a static magnetic field in frame S (where in S there is no electric field) then the momentum density in this frame is zero while the energy density is non-zero. Typically physicists like to think of things which have energy and for which there is a rest frame as something for which a mass can be defined. The proper mass density is found by transforming to the zero momentum frame, calculating the energy density and then dividing by c². For the magnetic field in S this will give something which is non-zero. Would you call this magnetic field "matter"? Would you say that the field has a non-zero mass density?

Edited June 29, 2009 by swansont
Poster retracted the question. Removed by mod.

[swansont]

I even agree with that statement. That doesn't mean I know what the author has in mind for a definition. Notice that he didn't refer to electrons? What are we to conclude as to whether an electron is made of matter?

 

Electrons are leptons, and from that description, matter.

[Severian]

Please ignore this post.

Edited June 29, 2009 by Severian

[proton]

Electrons are leptons, and from that description, matter.

Thanks for the correction. Notice that it doesn't speak of protons, presumably because protons are systems composed of quarks and as such as a non-zero invariant mass. A system composed of two photons moving in opposite directions also has a non-zero invariant mass.

[Severian]

I suppose a reasonable test of one's definitions would be to consider whether one would call a glueball matter or not.