E.6.4-6.8

E.6.4 State Hubble’s law:

The relationship between the distance of the galaxy and how fast it appears to be moving away from us is known as HUBBLE's LAW. This supports the theory that universe is expanding.

E.6.5 Discuss the limitations of Hubble's law

(Heinamenn Physics textbook Chris Hamper)

• The data points on the graph are scattered around the best fit line which indicates that there are random errors in the experiment
• since there are gravitational attraction between the galaxies, the speed of the recession should be decreasing as the time

E. 6.6. Explain how the Hubble constant may be determined:

(Heinamenn Physics textbook Chris Hamper)

Hubble's constant can be determine by the gradient of the best fit line as shown in the graph above. The value of this is not certain but is in the region of 72 Kms^-1 Mpc^-1

E6.7. Explain how the Hubble constant be used to estimate the age of the universe

The age of the universe can be calculated by using the equation:

 which is the same as:

We need to calculate this in seconds, thus we need to convert the distance into km

we now need to convert this into years

This calculation assumes that the velocity is constant. However, we know that the gravitational attraction slows down the galaxies thus the recession velocity that we measure today is much smaller than it was. This makes the value that we'd calculated too large. According to these measurements, the universe can;t be bigger than 1.36 x 10^10 years!

E.6.8. Solve problems involving Hubble’s law