Explanation of expanding universe

In summary, the universe is described as a 3-dimensional expanding manifold without a boundary, which can be visualized as a sheet of paper or a balloon surface. This mathematical concept does not require an embedding space into which it expands, and therefore, there is no evidence to support the idea that the universe is expanding into anything. The concept may be difficult to grasp due to our everyday experience, but it is a valid mathematical model of the universe.
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I once asked a physicist to explain what the universe expands into, and he gave me the analogy of raisins in bread dough. That the raisins represents galaxies, galactic clusters, etc...and as the universe (bread dough) expands, the galaxies (raisins) move apart. But this analogy assumes that the bread dough expands into the air around it, so I'm still unclear on what the universe is said to expand into.
Can anyone clarify? Thanks in advance!
 
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We have no evidence to support the idea that there is anything that the universe is expanding into.
 
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Mathematically it's quite simple: the universe is described by a 3-dim. expanding manifold without boundary (a 2-dim. manifold without can be visualized as an infinite sheet of paper, a surface of a balloon, a surface of a donut, ...); this mathematical concept does not require any embedding space, so the 3-dim. manifold can be described mathematically without a higher dimensional space into which it is embedded and into which it expands (a 2-dim. surface of a balloon can be described without the embedding into the 3-dim. space we ar used to).

So the only problem is that your everyday experience confused you b/c you are not able to think about these manifolds and their expansion w/o thinking about an embedding (whereas mathematically this embedding is not required).

So a 2-dim. model of our 3-dim. expanding universe would be a 2-dim. expanding sheet of paper with stars, galaxies, ... on this sheet of paper - but without the 3-dim. space into which the sheet is embedded.
 
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1. What is the expanding universe?

The expanding universe refers to the observation that the galaxies in our universe are moving away from each other at an increasing rate. This suggests that the universe is expanding, and the distance between objects is getting larger over time.

2. How was the expanding universe discovered?

The expanding universe was first discovered by astronomer Edwin Hubble in the 1920s. He observed that the light from distant galaxies appeared to be "redshifted," meaning that the wavelengths were stretched out, indicating that the galaxies were moving away from us.

3. What is causing the universe to expand?

The exact cause of the universe's expansion is still unknown, but it is believed to be driven by a force called dark energy. This force is thought to make up about 68% of the total energy in the universe and is responsible for the accelerating expansion of the universe.

4. Will the universe continue to expand forever?

Based on current observations and theories, it is believed that the universe will continue to expand forever. However, this is not a certainty, and there are still ongoing studies and research to better understand the fate of the universe.

5. How does the expanding universe affect objects within it?

The expanding universe does not have a significant effect on smaller objects, such as planets and stars, as they are held together by their own gravity. However, the expansion does affect larger structures, such as galaxies and galaxy clusters, as they are pushed further apart from each other.

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