# Tag Info

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Dark matter galaxies are possible but very speculative. On a theoretical level, they are hard to form because dark matter interacts only gravitationally (see Anders Sandberg's answer), which makes it hard to lose energy and become bound structures. On an observational level, they would be hard to detect. Gravitational lensing can do something, but since one ...

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Probably not. Dark matter should really be called "transparent matter" since it does not interact with light. This has an important consequence: it is hard for dark matter - whatever it is - to lose energy by radiating. This is why normal matter can form clouds that accrete into dense regions that in turn become galaxies and stars: energy is ...

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Matter is the stuff you are made of. Antimatter is the same as matter in every way, looks the same, behaves the same, except its particles have electrical charges opposite to matter. E.g., our electrons are negatively charged, whereas a positron (an antimatter "electron") is positively charged. The positron is the "anti-particle" of the electron. When a ...

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Tl;DR Detection via polarized light - Antimatter interaction with polarized light could be detected by vector rotation; We're mostly sure, because absence of gamma rays and characteristic Faraday polarization indicates absence of observable antimatter in meaningful amounts. Long answer I do believe @userLTK to be correct on his comment. To my limited ...

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The proton-proton chain ultimately converts four protons into one helium nucleus. The charge of the 4 protons was balanced by 4 electrons, but helium contains 2 protons (and 2 neutrons), so it only needs 2 electrons to be balanced. As you point out, the process of converting a proton to a neutron releases a positron (and an electron neutrino), and that ...

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Yes, it is a thing. Weakly Interacting Massive Particles (aka WIMPS) are thought to come in matter and anti-matter forms and have a self-annihilation cross-section in order to produce the "correct" amount of dark matter (in relation to photons) that we measure today. As the opening paragraph of the wikipedia article on WIMPS states - there are a number of ...

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Could dark energy (the mysterious accelerating expansion of the universe) be explained by "negative gravity"? But it already is "negative gravity". In general relativity, the stress-energy tensor $T_{\mu\nu}$ describes the energy, momentum, and stress of matter in spacetime. Through the Einstein field equation, it is connected with Ricci curvature $R_{\mu\... 7 Black holes are not "made of matter". They are better described as structures of gravity/warped spacetime. However, they do grow when absorbing things with positive mass-energy. Antimatter still has positive mass-energy, so the black hole cheerfully gobbles it up. Now, exotic matter with negative energy density might indeed decrease the size of the black ... 5 They are not replaced. Fusion in ordinary stars means actually many processes, neutrinos are involved most commonly in these:$p + p \rightarrow D + \nu_e + e^+T \rightarrow He_3 + \nu_e + e^+$The created positrons (very) quickly find an electron to annihillate into two (sometimes 3) gamma photons:$e^- + e^+ \rightarrow 2 \gamma\$. As you can see, ...

5

First it will be important to consider the term 'relativistic speed'. If by that you mean something like 0.1c, it will only change the colour of the stars as you mentioned in the bounty description. However, if it means something with higher Lorentz Gammas (like 0.9c or 0.99c), all other relativistic effects come into play. There's relativistic beaming and ...

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It would look very similar, but tiny differences are suspected, see e.g. this LHC experiment. Here a list of more antimatter experiments at CERN. See also CP violation on Wikipedia hinting towards tiny differences between matter and antimatter. Immediate consequence: The CP violation parameter of the CKM matrix in this Wikipedia article would be different,...

4

To answer your second question first: Yes, antimatter does exist in the same space as matter. In fact, the universe creates antimatter (and an equal amount of matter) every day as a matter of course in events like lightning strikes and supernovae, and even in certain nuclear decays. Humans create it in particle accelerators for research and for commercial/...

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It would be more accurate to say that a black hole eventually turns whatever falls in it into equal quantities of matter and antimatter. The difference between matter and antimatter is defined by some conserved (or approximately conserved) quantum numbers. For example, matter baryons and quarks have positive baryon number, while antibaryons and antiquarks ...

4

Gravitational lensing observations suggest that there is a large mass of dark matter on either side of the bullet cluster, which is actually one of the major pieces of evidence that dark matter does indeed exist. This dark matter essentially "left behind" the majority of the normal matter in the galaxies it was with as two galaxy clusters collided ...

3

Yes it is. See this 2012 blog post by Paul Gilster: https://www.centauri-dreams.org/2012/05/17/powering-up-the-antimatter-engine/ It says things like this: Antimatter in space is an idea that James Bickford (Draper Laboratory) analyzed in a Phase II study for NASA’s Institute for Advanced Concepts, for he had realized that high-energy galactic cosmic ...

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Energy can indeed transform into matter - for example pair production; but this creates equal amounts of matter and anti-matter.

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Antimatter is present on Earth and is being naturally created all the time (by Beta decay) as well as being created as product of cosmic ray collisions and in particle accelerators. However the universe appears to be principally made of matter and so the antimatter thus created is annihilated: and although the production of antimatter through nuclear decay ...

3

I'm assuming that by "inside the black hole" you mean inside the event horizon. In that case, the answer is no. The local space of a particle inside the event horizon is the same as outside - The difference is just that the spacetime points inside and out are causally disconnected. Right at the singularity, no one knows for sure what happens, but I think ...

3

A pretty good site for quick explanations is the Particle Adventure Anti Matter Dark Matter Anti Matter is really quite simple and very similar to regular matter. It just happens to explode violently when it touches regular matter - like a positron (Positive Electron) and an electron (negative) will touch and evaporate into a pair of gamma rays. The ...

2

Matter and antimatter aren't perfectly symmetric, when following the "forward" direction of time. This is commonly called charge-parity violation. It's assumed, that this asymmetry caused an excess of matter in the early stages of the Universe after the Big Bang, annihilating almost all antimatter, and leaving behind matter.

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You would/should be able to detect the annihilation of electron-positron pairs at the boundary between normal-matter and anti-matter space. This has a distinctive energy and so could be identified unambiguously. For an example of the detection of electron-positron annihilation see this NASA news item.

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There are two major points about this, I think. First, and ultimately most importantly, is that if we have matter here, and they have antimatter over there, then somewhere in between we must have a region that transitions from matter to antimatter. Even if this region is located in the intergalactic medium, where densities are typically very low, ...

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This assumes that when a pair particle-antiparticle is created, a bias towards antiparticles being captured and particles escaping must exist. No such assumption or bias exists. As far as we know the universe treats anti-particles just like particles with different properties (e.g. charge is opposite compared to the corresponding particle). Otherwise, ...

1

Matter and antimatter particles are always produced as a pair. This particle physics' process is called pair production. If antimatter is detectable, it means that the antiparticle of a matter-antimatter-particle-pair was able to survive long enough to be detected, for instance due to relativistic effects, as explained e.g. by the Hyperphysics page on muons: ...

1

Many products are created by Matter and Anti Matter collision but is dependent on what matter antimatter that is annihilating. Example electron and a positron annihilate create 2 photons. Proton-anti-proton annihilation produces as many as nine mesons have been observed. If there were equal amounts of matter and antimatter in the beginning we would now see ...

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I'm stealing a bit from other answers, just to clarify the point here. What follows is not exactly how it all happens, but should clarify how electrons and positrons are balanced. The key to the answer is in this part of the reaction: two hydrogen atoms become one hydrogen atom. A hydrogen atom is made of one electron and one proton and zero or more ...

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It's kind of a strange question but I'll give it a shot. It depend, kind of obviously, on how much of the "space dust" hits the earth. Estimates vary pretty widely on how much dust from space hits the Earth anyway, by this site, between 5 and 300 metric tons per day. Lets start with the low end estimate, 5 metric tons (5,000 KG) per day. Antimatter ...

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The consensus opinion of physicists is that antimatter has mass, and it is attracted to other massive objects by gravity in exactly the same way as matter: Antimatter isn't anti-gravity. Proving this is difficult. It is hard to obtain enough antimatter in one place to observe any gravitational interactions. The best observations aren't even able to ...

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Yes, common believes are because gravitation has effect on particles with mass. Antimatter are equivalent to there counterpart, sharing the same mass but opposite charges. Therefore, antimatter is attracted by gravitation. But, this is still not experimentally proven, therefore a more theoretical explanation of the gravitational interaction. Some researches ...

1

This is from my general relativity course from many years ago. I don't think there have been any discoveries since that would invalidate it. There is this thing called the no hair theorem for black holes. It states that only a few quantities apply -- mass, angular momentum, and charge I think. Most notably, baryon number is NOT one of the few ...

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