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Does the Universe expand by stretching or creating space?

๐ŸŒˆ Abstract

The article discusses the expansion of the universe and whether it occurs through the stretching of space or the creation of new space.

๐Ÿ™‹ Q&A

[01] Does the Universe expand by stretching or creating space?

  • The expansion of the universe can be interpreted in two ways:
    • Space is stretching, causing light, gravitational waves, and other signals to be lengthened and redshifted as they travel through the expanding space.
    • New space is being created, filling in the "gaps" opened up by the cosmic expansion.
  • Both interpretations have their usefulness, but they are fundamentally limited analogies that can fail if used incorrectly.
  • The expansion of the universe is real, but no single analogy perfectly captures the underlying physics.

[02] What is the relationship between the content of the universe and the expansion of space?

  • General relativity relates the amount, distribution, and types of energy in the universe to the geometry and evolution of spacetime.
  • In a completely empty universe, space would be flat and static.
  • With a single point mass, space would be curved according to the Schwarzschild metric, but still static.
  • However, when the universe is uniformly filled with matter, radiation, and other forms of energy, general relativity mandates that the universe must expand or contract over time.
  • The Friedmann equations describe this evolution of the expanding or contracting universe.

[03] How do we observe the expansion of the universe?

  • We cannot directly measure or experiment on space itself. Instead, we observe the effects of an expanding universe on measurable quantities like the redshift of light from distant galaxies.
  • As the universe expands, the density of matter decreases, while the wavelength of radiation increases (redshift).
  • Measurements of redshift, gravitational time dilation, and other effects have all been found to precisely match the predictions of general relativity.

[04] What are the different components of the current universe?

  • Today, the universe is composed of:
    • 0.008% radiation (photons)
    • 0.1% neutrinos
    • 4.9% normal matter
    • 27% dark matter
    • 68% dark energy
  • The expansion rate and evolution of the universe is determined by the relative amounts of these different energy components.

[05] How do the different energy components affect the expansion of space?

  • For radiation, the "space stretches" analogy works well, as the wavelength of light increases with the expansion.
  • For dark energy, which has a constant energy density, the "creation of new space" analogy is more appropriate, as the total dark energy increases as the volume expands.
  • Neither analogy works universally - they each capture aspects of how different energy forms interact with the expanding spacetime.
Shared by Daniel Chen ยท
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