Starship Asterisk*

I read its possible to have an Antimatter Galaxy, This troubles me.

http://www.space.com/scienceastronomy/a ... 30929.html

Troubles me because I thought all the antimatter annihilated at the Big Bang. And the universe is whats left over.

Would it be possible to see a Antimatter Galaxy? If it has mass, then like dark matter should be observable?
Is antimatter still annihilating matter and the reason behind the increase in expansion?

If I had a hand full of neutrons, and a hand full of positrons and put them together, where does all that energy come from?

Neutral Universe collides with positive Universe?

mark swain wrote:Would it be possible to see a Antimatter Galaxy? If it has mass, then like dark matter should be observable?

From the article to which you linked...

"Generally it [an antimatter star or galaxy] would look the same as a matter star or galaxy to most of our instruments."

Rob

So an anti sub particle of space that we have never seen or no knowledge about could be annihilating with positive space and causing expansion?

mark swain wrote:Would it be possible to see a Antimatter Galaxy?

An Antimatter Galaxy would emit antiphotons.
However, antiphotons are indistinguishable from photons.

mark swain wrote:If I had a hand full of neutrons, and a hand full of positrons and put them together, where does all that energy come from?

Well neutrons decay by emission of an electron, an antineutrino and a proton
so if you put one neutron and one positron (an anti-electron) together
it would generate a proton, a neutrino and two gamma rays
(from the destruction of the positron & electron).

I don't know what "a hand full of positrons" is exactly but
electrostatically & quantum mechanically it would be hard to hold in one's hand.

neufer wrote:An Antimatter Galaxy would emit antiphotons.
However, antiphotons are indistinguishable from photons.

That statement suggests they are different, but we can't determine the difference. In fact, photons and antiphotons are exactly the same particles, since photons are their own antiparticles.

mark swain wrote:So an anti sub particle of space that we have never seen or no knowledge about could be annihilating with positive space and causing expansion?

No. First of all, it is unclear what you mean by a "particle of space". Space isn't made of particles. Space isn't "positive" or "negative". Second, particles and their antiparticles annihilate and produce photons. We are quite good at detecting photons, and there's no reason (theoretical or observational) to believe that photons are driving universal expansion.

Chris Peterson wrote:

neufer wrote:An Antimatter Galaxy would emit antiphotons.
However, antiphotons are indistinguishable from photons.

That statement suggests they are different, but we can't determine the difference. In fact, photons and antiphotons are exactly the same particles, since photons are their own antiparticles.

same = indistinguishable by definition.

makc wrote:

Chris Peterson wrote:

neufer wrote:An Antimatter Galaxy would emit antiphotons.
However, antiphotons are indistinguishable from photons.

That statement suggests they are different, but we can't determine the difference. In fact, photons and antiphotons are exactly the same particles, since photons are their own antiparticles.

same = indistinguishable by definition.

Yes, but the converse is not true: indistinguishable does not necessarily mean the same. Neufer's observation did not make it clear that photons and antiphotons are identical.

define "same" then?

makc wrote:define "same" then?

In this context, it means having identical physical properties. "Indistinguishable" simply means that we lack the ability to perceive a difference, not that there is no difference. There could be entirely different particles, for instance, that we can't distinguish from one another by observation.

Fantastic, A complete mirror image. Including space time. And stuff we haven't discovered yet.

Who knows what happens when a unknown sub atomic anti particle interacts with its composite. Inflation of expansion?

Chris Peterson wrote:

makc wrote:define "same" then?

In this context, it means having identical physical properties. "Indistinguishable" simply means that we lack the ability to perceive a difference, not that there is no difference. There could be entirely different particles, for instance, that we can't distinguish from one another by observation.

http://en.wikipedia.org/wiki/Identical_particles wrote:
<<Identical particles, or indistinguishable particles, are particles that cannot be distinguished from one another, even in principle. Species of identical particles include elementary particles such as electrons, as well as composite particles such as atoms and molecules which are in precisely the same quantum state. The fact that particles can be identical has important consequences in statistical mechanics. Calculations in statistical mechanics rely on probabilistic arguments, which are sensitive to whether or not the objects being studied are identical. As a result, identical particles exhibit markedly different statistical behavior from distinguishable particles. For example, the indistinguishability of particles has been proposed as a solution to Gibbs' mixing paradox.>>

Chris Peterson wrote:

makc wrote:define "same" then?

In this context, it means having identical physical properties.

apart from what neufer already said, we "distinguish" things by finding one (or more) properties that are different. having zero different properties is exactly "indistinguishable", or "same" per your definition.

Chris Peterson wrote:"Indistinguishable" simply means that we lack the ability to perceive a difference, not that there is no difference. There could be entirely different particles, for instance, that we can't distinguish from one another by observation.

Perhaps you suggest there is some fundamental difference between things that "might have different properties that we do not know of" and "things that we know they do not have any other properties that may be different", but what does this mean in this context? As long as you speak about photon as some concept defined in particular physics theory, it's case #2, but when you speak about photon as something real flying right out there, it's case #1.

Does not everything in the universe have its anti counter part?

mark swain wrote:Fantastic, A complete mirror image. Including space time. And stuff we haven't discovered yet.

Who knows what happens when a unknown sub atomic anti particle interacts with its composite. Inflation of expansion?

There is no evidence to support an anti-universe (or anti-galaxy), nor what type of symmetry it might exhibit. Current models suggest that matter and antimatter formed in nearly equal amounts in the early universe and annihilated each other. A slight imbalance of matter over antimatter resulted in the universe we see today. However, annihilation is well understood in physics, and has nothing to do with inflation of expansion. In models of the early universe, inflation happened before the universe was cool enough for particles (or anti-particles) to form.

So why is it possible to make anti matter?

Mark, you know that because of E = mc^2, energy and matter are interchangeable. When you convert energy to matter, the particles you produce are going to be half matter and half antimatter. Always in pairs.

Why the early universe ended up with an unbalanced "matter check registry" as Chris pointed out, no one yet knows.

neufer wrote:

http://en.wikipedia.org/wiki/Identical_particles wrote:
<<Identical particles, or indistinguishable particles, are particles that cannot be distinguished from one another, even in principle. Species of identical particles include elementary particles such as electrons, as well as composite particles such as atoms and molecules which are in precisely the same quantum state.

That's a whole different definition than I'm talking about, and a whole different subject.

makc wrote:apart from what neufer already said, we "distinguish" things by finding one (or more) properties that are different. having zero different properties is exactly "indistinguishable", or "same" per your definition.

If two things have zero different properties, they are indistinguishable. But calling two things indistinguishable does not automatically mean they have zero different properties, which is why I quibbled with Neufer's use of the term. That's all.

Perhaps you suggest there is some fundamental difference between things that "might have different properties that we do not know of" and "things that we know they do not have any other properties that may be different", but what does this mean in this context? As long as you speak about photon as some concept defined in particular physics theory, it's case #2, but when you speak about photon as something real flying right out there, it's case #1.

All I meant is that photons and antiphotons are the same thing. Maybe a better way of expressing that is there's no such thing as an antiphoton, except as a synonym for photon. Theory and observation tell us that photons are their own antiparticles. If you simply say that photons and antiphotons are indistinguishable, you create the potential for confusion, since that doesn't necessarily mean the two are the same.

mark swain wrote:Does not everything in the universe have its anti counter part?

No.

Chris Peterson wrote:

mark swain wrote:Does not everything in the universe have its anti counter part?

No.

If they are looking for anti matter galaxies, then surly, those antimatter galaxies must have the complexities of our milky way?

http://www.space.com/businesstechnology ... unter.html

Chris Peterson wrote:If two things have zero different properties, they are indistinguishable. But calling two things indistinguishable does not automatically mean they have zero different properties, which is why I quibbled with Neufer's use of the term. That's all.

I am not trying to attack your attack on Neufer's use of the term, actually, it's just that in my everyday use of terms (or actually their russian equivalents) I make no such distinction. E.g., your statement is

zero different properties => indistinguishable

and mine is

zero different properties <=> indistinguishable

because I don't see what else 'indistinguishable' could mean.

If you simply say that photons and antiphotons are indistinguishable, you create the potential for confusion, since that doesn't necessarily mean the two are the same.

I see, true teacher has to think about things like these

mark swain wrote:If they are looking for anti matter galaxies, then surly, those antimatter galaxies must have the complexities of our milky way?

They aren't so much looking for antimatter galaxies as they are looking to rule out their existence. Theory says that they are unlikely to exist, because there isn't enough condensed antimatter in the Universe to form stars or galaxies. You won't find many astronomers who expect to find antimatter galaxies, but that doesn't mean it isn't worth looking for their signatures. In this case, finding nothing is as useful as finding something.

If antimatter galaxies exist, they are extremely rare- certainly there are vastly fewer of them than ordinary matter galaxies. The Universe (at least, the observable Universe) is made up almost exclusively of ordinary matter.

makc wrote:

Chris Peterson wrote:If you simply say that photons and antiphotons are indistinguishable, you create the potential for confusion, since that doesn't necessarily mean the two are the same.

I see, true teacher has to think about things like these

Which is fine except that that was NOT what Chris had originally stated:

Chris Peterson wrote: "Indistinguishable" simply means that we lack the ability to perceive a difference, not that there is no difference.
There could be entirely different particles, for instance, that we can't distinguish from one another by observation.

Quantum statistics define the term "indistinguishable" not humans.

The ability of two electrons to share the same orbital or of three up quarks to form a hadron was clear proof that these fermions were NOT "indistinguishable." The two electrons were later found to have different spins while the three quarks were defined to have different "colors."

Feynman once suggested that there was just one electron in the whole universe that zigzagged back & forth in time to create all the (~10⁸⁰) observed electrons & positrons. If you simply state that all electrons are identical, you might also create the potential for confusion that, in fact, there is just one electron in the universe.

neufer wrote:Quantum statistics define the term "indistinguishable" not humans.

Nonsense! There are many different meanings for "indistinguishable", and all are defined by humans.

The particular definition you are using here is just one, and isn't the one I'm using (again, this shows why the term is likely to create confusion). Electrons are indistinguishable in the sense that there are no differences at all in any physical properties between them. Photons are not indistinguishable in this sense: every photon in the Universe may have slightly different physical properties, and with good enough measuring equipment each could be distinguished from the others. Yet another meaning, which is the one most of this discussion has concerned, involves distinguishing between types of entities. An individual photon and antiphoton are potentially distinguishable, because they have different physical properties (such as energy). As a class, photons and antiphotons are not distinguishable, because there is no property class of one that isn't shared by the other- because they are the same type of particle. It is all these different meanings of "indistinguishable" that make it a poor choice of wording in the original statement.