Question

Cosmic acceleration and dark energy

Q: How do we measure the changes in the expansion rate?

Q: What is a standard candle? Why are supernovae useful as standard candles?

Q: What is so bizarre about the universe accelerating? What are the possible explanations for this? Which solution is the least radical?

Q: Why is dark energy invoked to explain the accelerated expansion?

Answer 1

1.We measure the changes in expansion rate by by comparing the apparent brightness of distant standard candles to the redshift of their host galaxies.

2. A standard candle is a class of objects whose distances can be computed by comparing their observed brightness with their known luminosity. By which we find the distances of galaxies

since objects that are further away appear dimmer, we can use the observed brightness of these supernovae to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred.

3.The universe is said to be expanding continuously, and it is said by some scientist that the universe is expanding beacuse of a mysterious force which is said to be dark energy.

4.the universe is going through a phase of accelerated expansion. Dark Energy was invoked to drive this acceleration.

Dark Energy is a hypothetical form of energy that exerts a negative, repulsive pressure, behaving like the opposite of gravity. It has been hypothesised to account for the observational properties of distant type Ia supernovae, which show the universe going through an accelerated period of expansion. Like Dark Matter, Dark Energy is not directly observed, but rather inferred from observations of gravitational interactions between astronomical object