I’m really curious about how the universe’s expansion works and what keeps it going. A thought crossed my mind: could it be mainly because of the law of conservation of energy?
In: Planetary Science
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Distances between groups of galaxies get larger. There is no deeper “how”, that’s just what happens. There is a bit more space between them than there was yesterday.
> And What keeps it expanding?
If there is no force on an object, it keeps moving in the same direction at the same speed. The expansion of the universe works pretty similarly. Without any force it would keep expanding in a constant way.
* Gravity slows the expansion. That was more important in the early universe when everything was closer together.
* Something we call dark energy speeds up the expansion. Today that is more important, which means the expansion speeds up a bit. It’s still slow on human timescales. Distances increase by ~1% every 140 million years.
Congratulations on asking one of the biggest unanswered questions in physics…..
No one knows. But the issue isn’t that it keeps expanding (that could happen through the initial impulse from the big bang). The issue is that its rate of expansion is increasing, which under every current theory of physics, would require more energy. Since that energy source can’t be located, it’s known as “dark energy”.
So far we just call whatever is making it expand “dark energy”, which is something of a placeholder for “we don’t know”.
If anyone can actually prove anything that answers your question, there’s a Nobel Prize waiting for them.
No. Exactly the opposite. The universe expanding means that at large (ie universe) scale, energy is NOT conserved. Based on our current theories, for this expansion to occur “new energy” must be added to the universe – we call it dark energy. Dark energy is just a placeholder name – we don’t know what it is but if our current theories are correct, then there must be some kind of energy that causes the expansion. Since this adds to the total energy in the universe – conservation of energy is violated (again this is in VERY large scales, bigger than galaxies kind of scale.) In any kind of human level physics, it is still convenient to use the principle of conservation of energy to predict outcomes.
But to your first question – we have very little idea what keeps it going. It is one of those things where we believe we can measure it but have no explanation for it. If you want to dig a little deeper – different measures of the expansion rate appear to give different results (kinda hard to measure on galactic scales so these are indirect measures). We call this the Hubble Tension. (ie we are tense about the fact that different methods give different measures of the rate of expansion.. /jk) Resolving this discrepancy is on the cutting edges on the physics of cosmology today.
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