In spacetimes like these, no cosmic expansion is present. There’s no change in the distance or the light travel time between any points within this spacetime. With just one (or fewer) sources of matter inside and no other forms of energy, these “model universes” really can be static.
Spacetime is continuously expanding, meaning the space between galaxies is constantly growing larger over time, as described by the theory of general relativity; essentially, the fabric of spacetime stretches, causing distant objects to appear further away from each other. g. As an infinite space grows, it remains boundless.
Indeed, the literature (both professional and popular) sometimes characterizes these as limits where the gravitational attraction overwhelms the degeneracy pressure due to the Pauli exclusion principle.
It’s important to note that the degeneracy pressure is not the same as the Pauli exclusion principle. The former is a macroscopic manifestation of the latter. A transformation occurs when the gravitational force becomes strong enough to overcome the degeneracy pressure. However, it’s crucial to understand that this transformation does not violate the Pauli exclusion principle at the particle level.
As to what that “something” is, in the case of white dwarfs, we have a pretty good idea. Crudely put, we can smash electrons and protons together, borrow some neutrinos, and presto: we have neutrons. This process transforms the degenerate matter inside a white dwarf into a new state of matter called ‘neutronium,’ which is the material from which the neutron star is made.
The TOV limit is far more mysterious. What happens must be better understood. There is speculation that the neutrons may break down into constituent quarks, forming some quark matter—quark-gluon plasma.
Guess—but this may not work, as we now have even more fermionic degrees of freedom than before, and we create even more quarks at high energies. We do not have a robust theory, and it may require a working quantum theory of gravity to allow us to reach firm conclusions about how such things unfold. The necessity and potential impact of such a theory are significant. We know that there is an upper limit to the mass of neutron stars and that they do collapse into likely black holes, but how it unfolds, I think, remains largely unknown and poorly understood.
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The Big Bang equations contain a scale factor, which doubles the separation between galaxies if it doubles in size. For every gravitational pull in one direction, there will always be enough mass in the other direction to balance it out.
Let’s clear up the most widespread misunderstanding of physical cosmology. No, spacetime is not expanding. It is also not contracting. It is not even standing still. None of these words are meaningful when considering what appears in the equations. This is a critical point that, once understood, will shed light on many aspects of cosmology.
These equations (the Friedmann equations, which are just a specific form of Einstein’s field equations for gravitation) depict something much more pedestrian. Never mind the fleeting notion of spacetime; the equations are about the gravitational field (the metric of spacetime) and matter. Moreover, it is a matter that is flying apart. More specifically, the density of matter decreases on average over time.
Emphasis on “average.”. That is because it only applies to matter on a large scale, distant lumps of matter not bound to one another by a gravitational force.
Lumps of matter nearer to each other—galaxies in a cluster, stars in a galaxy, planets in a solar system, atoms in your body—are all bound together by gravitational, electromagnetic, or short-range nuclear forces. That is to say, these lumps or particles.
S of matter stopped flying apart a long, long time ago.
So, no, you are not expanding (unless you overeat, but that has nothing to do with cosmology). The Earth is not growing. The solar system is not expanding; neither is the Milky Way nor the Local Group of Galaxies. The matter from which these things are made lost its momentum eons ago in a process that is well understood and is part of the standard theory that describes how large-scale structures form in our universe and how specific amounts of kinetic energy can be shed through a variety of mechanisms, ultimately turning into waste heat, allowing matter to “clump,” form structures, collapsing into stars and planets, including this Earth on which we live.
One of the reasons why this gets more confusing than necessary is that in cosmology, it is often convenient to express things using “comoving.
Science has confirmed that particles can appear out of nothing through quantum fluctuations. These are temporary changes in energy at a point in space. Most of the time, the particles pop in and out of existence, leaving nothing behind. Those so-called “virtual particles” are inherently random, by the way.
Inspired by virtual particles, the “ero energy universe hypothesis” suggests that you can create a universe from nothing. This hypothesis proposes that the universe could be a matter of bookkeeping: if you regard gravity as negative energy potential, sum up all matter and energy in one column and all gravitational potential in the other; they cancel out one another. That way, you can not only get a universe from nothing, but the universe would still be nothing, only very unevenly distributed.
Moreover, such an event would be completely random, like the virtual particles. However, infinite universes would exist if time did not exist before the universe. This concept ”refers to the arrow of time as we experience it, which may not have existed in the same way before the universe. Most of these hypothetical universes would pop out of existence immediately, sometimes so fast that they could hardly be said to have existed. However, a few have the suitable properties to expand to a universe; some would even allow stars, planets, and Quorans to form.
This is not the only hypothesis about how you get a universe, but it is exquisite in that it is self-contained and must start from nothing. Other hypotheses, like previous big crunches or black holes in predecessor universes, do not have this same level of elegance and self-containment.
None of these hypotheses, including the zero-energy universe hypothesis, violates physics as we know it. We cannot test any of them because the conditions in the early universe were so extreme that we do not have the physics to predict what happened then, and thus, we cannot peek at the moment of beginning.
In spacetimes like these, no cosmic expansion is present. There’s no change in the distance or the light travel time between any points within this spacetime. With just one (or fewer) sources of matter inside and no other forms of energy, these “model universes” really can be static.
As to what that “something” is, in the case of white dwarfs, we have a pretty good idea. Crudely put, we can smash electrons and protons together, borrow some neutrinos, and presto: we have neutrons. This process transforms the degenerate matter inside a white dwarf into a new state of matter called ‘neutronium,’ which is the material from which the neutron star is made.
The TOV limit is far more mysterious. What happens must be better understood. There is speculation that the neutrons may break down into constituent quarks, forming some quark matter—quark-gluon plasma.
These equations (the Friedmann equations, which are just a specific form of Einstein’s field equations for gravitation) depict something much more pedestrian. Never mind the fleeting notion of spacetime; the equations are about the gravitational field (the metric of spacetime) and matter. Moreover, it is a matter that is flying apart. More specifically, the density of matter decreases on average over time.
Emphasis on “average.”. That is because it only applies to matter on a large scale, distant lumps of matter not bound to one another by a gravitational force.
Lumps of matter nearer to each other—galaxies in a cluster, stars in a galaxy, planets in a solar system, atoms in your body—are all bound together by gravitational, electromagnetic, or short-range nuclear forces. That is to say, these lumps or particles.