# Tag Info

## New answers tagged expansion

4

The universe started with "big bang" is a slogan for "There was a time when the universe was hot and dense, and this time may be considered to be the start of the universe, and the start of time." The universe has (as far as we know) always been infinitely large. That's not certain, but we have no evidence contradicting it. The universe ...

4

This answer to the question “Is the Hubble constant dependent on redshift?” gives the formula (a form of the Friedmann equation) for the Hubble parameter $H(z)$ as a function of redshift $z$: $$H(z)^2 = H_0^2 \left[ (1+z)^4 \Omega_r + (1+z)^3 \Omega_M + (1+z)^2 \Omega_k + \Omega_\Lambda \right]$$ where the $\Omega$ terms are the fractional densities in ...

1

Your intuition is correct - a moving source emitting wavefronts periodically will be closer to the previously emitted wave in the direction of motion, and farther from the previously emitted wave in the opposite direction - see the simulation here. You are also correct that the size of the effect depends on the speed of the observer relative to the speed of ...

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