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37 votes
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At the Big Bang, when everything was close together, why did it not "collide", violating Planck length or Pauli Exclusion Principle?

The Pauli Exclusion Principle forbids two indistinguishable fermions occupying the same quantum state. It does not prevent them getting arbitrarily close together so long as they have very different ...
ProfRob's user avatar
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28 votes

What's the percentage of strange matter inside a star at any time?

Zero. Normal stars are not dense enough to produce strange matter. They have regular matter only (neutrons and protons). Strange matter has been hypothesized to form inside neutron stars, but this is ...
Prallax's user avatar
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16 votes
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Is normal matter always accompanied by dark matter and vice versa?

We lack the precision to say that there aren't regions where there is matter without dark matter or vice-versa. But what is clear is that the ratio of dark matter to normal matter, which is (or needs ...
ProfRob's user avatar
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10 votes
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What's the percentage of strange matter inside a star at any time?

Let me first underline two specific definitions of @Alexandre: We are looking for "matter", that means a finite region in space in thermal equilibrium. And we are looking for "...
Klaus H's user avatar
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9 votes

Is there any proof of space being created?

This is an intriguing proposition, but I would ask how your hypothesis explains that the universe appears to be flat? That is with $\Omega_M + \Omega_\Lambda = 1$. The evidence for this comes from ...
ProfRob's user avatar
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9 votes

Does matter accumulate just outside the event horizon of a black hole?

Several wonderful yet technical answers have been given, and I cannot add anything to those very nice answers that explain why it is not useful to think black holes get "frozen" at their event ...
Ken G's user avatar
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9 votes
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Do we know how old the matter that makes us is?

The material (heavier than helium) that makes up the solar system was made in millions, if not hundreds of millions of stars that lived and died in the ~7 billion years between the formation of the ...
ProfRob's user avatar
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9 votes
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How is observable matter distributed in the universe?

I think the following is a fair summary. It's based on a fairly old study by Fukugita & Peebles (2004) but the numbers are quite reasonable. Your guess about stars dominating is way off. Most of ...
ProfRob's user avatar
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9 votes

Are liquids the rarest state of matter in the universe?

No, by far the rarest state of matter in the universe is Bose-Einstein Condensate. As far as we know BECs do not naturally occur anywhere in the Universe, and have only been realized under lab ...
TimRias's user avatar
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8 votes
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What explains the existence of energy/matter if it cannot be created or destroyed?

That's a very complicated question! First, let's remember that Moses didn't bring the Law of Conservation of Energy down from Sinai on stone tablets -- it's something that we've observed to be true ...
Mark Olson's user avatar
  • 7,640
7 votes

Does matter accumulate just outside the event horizon of a black hole?

Thought provoking cosmologists! I'm uber-late to this discussion as I see it has been ongoing for literally years and don't know if there is still anyone monitoring this thread, but here goes. I ...
Doug Klotz's user avatar
7 votes
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Scenarios: Abusing a black hole

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 ...
Anders Sandberg's user avatar
7 votes

Absorption of light by matter

It is the other way around. An isolated, point-like charged particle like an electron cannot absorb a photon. It is forbidden, because energy and momentum cannot be simultaneously conserved. Only ...
ProfRob's user avatar
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6 votes
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Why isn't the black hole white?

What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly. The disk is referred to as ...
ProfRob's user avatar
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6 votes
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What percentage of the hydrogen today has never been in a star

About 70% of the baryonic matter in the universe is hydrogen, with a mean density of about $4\times 10^{-29}$ kg/m$^3$. Most of the stars that have ever been born are still alive, since an average ...
ProfRob's user avatar
  • 155k
4 votes
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Why Helium could be produced in first minutes of big bang but not heavier elements

The triple alpha process requires very high densities, very high (but not too high) temperatures, and a good amount of time. Large stars have all three. In particular, they have millions of years ...
David Hammen's user avatar
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4 votes

Is there any proof of space being created?

As is always the case in physics, there is no proof. But if your scenario were true, it would have to be rather fine-tuned in order to create the observed expansion of the Universe. First of all, ...
pela's user avatar
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4 votes
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Are we made of stars we're seeing?

Stars really are immensely far, however it's a common misconception that the stars that you can see are millions of light years away. Most of the visible stars are a few tens to a few hundreds of ...
James K's user avatar
  • 125k
4 votes

Does matter accumulate just outside the event horizon of a black hole?

As I understand it, the presence of an event horizon (EH) from gravitational collapse is a case in which GR violates local causality in the outer (w.r.t. EH) universe. By Birkhoff theorem the EH can ...
Stefano Pinchetti's user avatar
4 votes

Is the dark matter just regular matter out of the observable universe?

Scientists do not know what dark matter is. It is a placeholder name. It is called "dark" for two reason: If it exists, it interacts at most very weakly with electromagnetic radiation. It ...
David Hammen's user avatar
  • 34.1k
4 votes

Is the dark matter just regular matter out of the observable universe?

If dark matter exists (rather than some strange rewrite of physical laws), then it is required to be all around us. It could not be simulated by the effects of normal matter at great distances. There ...
ProfRob's user avatar
  • 155k
3 votes

The Matter Anti Matter Asymmetry

Energy can indeed transform into matter - for example pair production; but this creates equal amounts of matter and anti-matter.
ProfRob's user avatar
  • 155k
3 votes

Why isn't the black hole white?

The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower ...
Steve Linton's user avatar
  • 10.3k
3 votes

When the universe expands does it create new space, matter, or something else?

The expansion of spacetime does not involve the creation of anything. What is happening in the process of expansion is the enlargement of the metric itself of the spacetime. Imagine this as any ...
ShroomZed's user avatar
  • 265
3 votes

Does matter accumulate just outside the event horizon of a black hole?

An observer falling into a black hole does not see himself fall into the singularity unimpeded. The black hole will always evaporate before infinity, therefore the infalling observer will fall to the ...
Smart guy's user avatar
3 votes

How does Hawking Radiation work exactly?

... but how does the other know how to take energy from the black hole? In order to understand this, you need to be familiar with the essence of this picture$^1$ including negative energy states ...
Ad Astra's user avatar
  • 258
3 votes
Accepted

What do "overdense" and "underdense" mean in cosmology?

Over- and underdensities are simply defined with respect to the mean density $\bar{\rho}$. That is, if $\rho(x) > \bar{\rho}$, then $\delta(x)$ is positive and you call it an overdensity, whereas ...
pela's user avatar
  • 38.7k
3 votes

Question re distribution of the baryonic matter in the Universe

The total baryonic mass density can be estimated by combining analysis of the cosmic microwave background, estimates of the primordial abundances of helium and deuterium and measurements of the Hubble ...
ProfRob's user avatar
  • 155k
2 votes
Accepted

What was the process of calculating how much darkmatter/matter/dark energy the observable universe consists of and how did it come at this conclusion

We are not actually measuring the $\Omega_r$,$\Omega_m$,$\Omega_{\Lambda}$. At first, we measure the distance modulus to certain celestial objects by using the standart candles in the astronomy. This ...
seVenVo1d's user avatar
  • 576

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