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How do scientists know that distant galaxies are made of matter and not antimatter?

Antimatter has identical properties as matter so it could form stars and planets too. Light emitted by antimatter stars is exactly the same as light from matter stars. The only thing that we receive from other galaxies is their light. So how can we know if distant galaxies are made up of matter or antimatter?

2007-10-16 19:10:04 · 8 answers · asked by jeffdanielk 4 in Science & Mathematics Astronomy & Space

The point of this question is not definitions. It is this: How do we know that distant clusters of galaxies are made up of the same kind of matter than we are (protons that are positively charged)? Why couldn't some of them be entirely anti-matter?

Superclusters of galaxies don't collide or exchange substances at all. They are completely isolated from each other.
And a photon is its own antiparticle.

2007-10-16 19:54:57 · update #1

8 answers

It's really more an issue of convention. We define "matter" to be the "stuff" that we readily observe (protons, electrons, etc.). Therefore the "other stuff" that is like our readily observed "stuff", but opposite in charge is dubbed "antimatter". It's really just us giving names to the "stuff" we see around us so we all know that we're referring to the same "stuff" and not different "stuffs" (physicists are a little strange about naming things). It could have just as easily been named the other way around or something else entirely.

However, since antimatter and matter destroy each other, the likelihood of galaxies of antimatter under this convention is low (otherwise these antimatter galaxies would destroy any matter galaxies they approached). Here's a good site for a better understanding of our general knowledge concerning antimatter: http://cyclo.mit.edu/~bmonreal/antimatter.html

2007-10-16 19:36:13 · answer #1 · answered by acamar_sirus 3 · 0 0

If you come to think about it, we might be living in an anti-matter world. Now, since we like the easier way to do things, no scientist likes to go around calling everything anti-matter when it would be easier to call it matter instead. So everybody goes around calling it matter. We don't know any different. But wouldn't it be surprising if we get a radio transmission from beings in another galaxy and the first thing they ask is; "So, what's it like living in an anti-matter world?"

2016-05-23 03:02:41 · answer #2 · answered by ? 3 · 0 0

Assuming large zones of antimatter exist, there would have to be some boundary where antimatter atoms from the antimatter galaxies or stars will come into contact with normal atoms. Even in the near vacuum of intergalactic space there are still large numbers of 'normal' molecules of gas and dust. In those boundary regions a powerful flux of gamma rays would be produced. This has never been observed despite deployment of very sensitive instruments in space to detect them.

2007-10-16 20:59:56 · answer #3 · answered by Anonymous · 0 0

We receive a lot of different types of radiation from other galaxies. Among others we can see x-ray sand gamma rays. If part of the universe were anti-matter, it would collide with ordinary matter and annihilate. Electron/positron annihilation would produce a characteristic 511keV gamma line. Since we don't see much of that energy, we know that there is not much matter-anti-matter annihilation going on. So unless something separates all of the anti-matter from the matter, there is no anti-matter.

2007-10-16 19:18:53 · answer #4 · answered by Anonymous · 1 0

Well, because of how we've defined it. We defined 'anti-matter' as being the same particles but with opposite charge (like the positron, the anti-matter of an electron).

Bascially, we decided to call the stuff we are made of as 'matter' and the stuff that is the exact opposite charge as 'anti-matter'. An alien civilization in another galaxy could be made up of what we call anti-matter, but to them it is just regular matter, and we are the anti-matter species.

It's all definitions!

I hope this helps!

2007-10-16 19:37:18 · answer #5 · answered by Anonymous · 0 0

In principle, it is possible. But matter exists throughout the universe, and would annihilate with antimatter if the two ever met. For that reason, we can be confident that everything we see is normal matter.

2007-10-16 19:36:26 · answer #6 · answered by Anonymous · 0 0

They wouldn't be photons, they'd be anti-photons and they'd be annihilated long before they got to our telescopes.

Doug

2007-10-16 19:30:35 · answer #7 · answered by doug_donaghue 7 · 0 2

Well you see we don't really know much of anything. This is all things about relative theory and what not. Basically we don't know.

2007-10-16 19:14:19 · answer #8 · answered by I have 0 characters to work with 3 · 0 2

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