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Expansion of the universe
Intermediate
Space itself stretches.
Space itself expands, stretching light wavelengths and carrying galaxies apart; there's no centre. The expansion accelerates today due to dark energy.
Like dots on an inflating balloon.
Galaxies aren't flying through space.
In more detail
The expansion of the universe means that space itself is stretching, carrying galaxies apart. The expansion is accelerating in the present era, driven by dark energy.
Real-world uses
- Expansion explains the redshifts of distant galaxies.
- Cosmological models describe the history and future of the universe.
- Cosmologists explain that light from distant galaxies is stretched because the space it travels through expands.
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Frequently asked questions
Is the universe expanding into anything?
No. Space itself is expanding, and there is no outside edge in which it expands.
Why is it accelerating?
Dark energy is the leading explanation, though its nature is not known.
Does expansion push galaxies apart in a room?
Not in a room or the solar system, since gravity and other forces hold these together against the expansion.
Related topics in Particle Physics & Cosmology
Galaxies · Milky Way · Hubble's law · Big Bang theory · Cosmic microwave background · Big Bang nucleosynthesis