30 votes
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How can the universe be hot or dense in the first moments after the big bang when it has no matter?

In Physics, hot is an adjective meaning at high temperature. Heat is a different concept. In the case of ordinary matter, the temperature can be associated with atomic speeds. However, it is possible ...
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29 votes
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How does it make sense for the universe to have started from a big bang?

The singularity at the start of the universe in the Big Bang model is not supposed to be understood as part of the smooth manifold of spacetime, precisely for this reason. The time function on ...
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22 votes

How does it make sense for the universe to have started from a big bang?

A “singularity” is shorthand for “a place where our current understanding of the laws of physics breaks down”. If we use our current model of the laws of physics (specifically general relativity) to ...
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18 votes
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Why did the quark epoch occur earlier than the lepton epoch?

The terms quark epoch and lepton epoch do not mean that is when those particles were created. As far as we know the Standard model particles were created at the end of the inflationary epoch and both ...
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12 votes

How does it make sense for the universe to have started from a big bang?

You're asking a mathematical question. Mathematics is a human invention. Sometimes it maps well onto the phenomena we see. Spacetime geometry is a case where, in the portion of the universe accessible ...
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9 votes

How does it make sense for the universe to have started from a big bang?

There are several problems with this argument. First, cosmological models having a singularity just means that they blow up as $t\to 0^+$ and aren't defined at $t=0$. That's interpreted as a ...
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7 votes

How can the universe be hot or dense in the first moments after the big bang when it has no matter?

Fundamentally, "matter" is manifestation of energy excitations of a universal, all-encompasing substrate (the vacuum or "aether" or spacetime - properly understood, these all refer ...
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5 votes

How does it make sense for the universe to have started from a big bang?

Physicists feel a great aversion to infinity-valued physical quantities. They call them singularities and usually say that the physics fails there. A mathematician would never say the mathematics ...
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4 votes

How can the universe be hot or dense in the first moments after the big bang when it has no matter?

Remember that when we talk about the big bang, all we can actually do is take the current universe and extrapolate the clock backwards in time. We do this using General Relativity ($\Lambda \mathrm{...
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3 votes

What implications to cosmology would it have if Webb Telescope probing the far end of our observable Universe finds out a large number of galaxies?

The current "bottom-up" idea of structure formation suggests that galaxies are built up over cosmic time from the mergers of lots of smaller galaxies. There is now plenty of chemical and ...
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1 vote

What is there at a point the universe hasn't expanded past yet?

If the universe is constantly expanding that means that there is a point the univese [sic] hasn't expanded past... Your premise is not necessarily correct. with that what would be past that point? ...
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1 vote

${}$Hawking radiation and Einstein-Cartan theory

I don't have any particular expertise in Einstein-Cartan theory, but I would caution against taking it seriously as describing real astronomical black holes. Even the simplest black hole solution, due ...
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