Expansion of the universe

In summary, this conversation discusses several topics related to the universe, including its final states, the velocity of recession of galaxies, the distribution of stars, and the value of the Hubble constant. The key points mentioned are the differences in the final states of the universe depending on its average density, the possibility of our galaxy occupying a central spot if the velocity of recession was proportional to the distance squared, the non-uniform distribution of stars in the night sky due to our view of the Milky Way galaxy, and the discrepancy in the age of the universe as determined by Hubble's calculations. The main problem faced by Hubble was the disagreement between his calculated age of the universe and other values.
  • #1
burak_ilhan
14
0
some HW question.Thanks for your help...


1)decribe the DIFFERENCE between the FINAL states of the universe a)if the average density of the universe is greater than the critical value b)if it is equal to the critical value

2)if the velocity of recession of the galaxies were not proportional to the distance (v=Hr) but rather proportional to the distance squared v=Hr^2 or proportional to some other power of the distance, then our galaxy would occupy a preffered, central spot in the universe?

3)if you look at the night sky, you see that the distribution of stars is not uniform.What main deviation from uniformity do you see, an to what is this deviation due?

4)the value of the Hubble constant that Hubble had deduced from the available data in 1936 was 1.6*10^5 (m/s)/(million light years) the corresponding expansion time is 1.9*10^9 years. how does compare with the age of the Earth and with the age of the globular clusters? with what problem was Hubble faced?
 
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  • #2
I probably should shoot this over to the Homework Help forum, but I think the regulars in this forum will provide more thorough answers.

(3) Assuming you have mostly light-pollution free skies and the proper time of night to view, most of the starlight you will see will be within a broad band that stretches all the way across the sky. This is the Milky Way galaxy viewed, of course, from our perspective on the inside. The Milky Way is a spiral galaxy in which most of the stars are configured into a flattened disk (as opposed to some other galaxies which are more like elliptical clouds of stars). Our view of this disk is edge-on, thereby resulting in the majority of starlight being focused within the band. Of course, we are not at the extreme edge of the disk...more like 2/3 the way out, and our region is still several thousand light years thick. So, we also see nearby stars (within a few hundred light years) that are "up/down" from us with respect to the overall disk. More distant stars are too faint. More distant stars within the disk are also too faint, but there are so many that they add up to the faint Milky Way band across the sky. Check it out with binoculars and you'll see many more stars in that region of the sky than in other regions. If the Milky Way is not visible to you (light pollution or whatever), then you're seeing an essentially random distribution of the brightest nearby stars...with a few star clusters here and there (a result of star formations from within the same original nebula).
 
  • #3
You should really show us what you've done so far, but here are few very brief answers/pointers:

1) a)Big crunch b)finite size

2) Think about a co-moving sphere, can the points on the surface of the sphere all be moving apart at a velocity proportional to r2?.

3) Phobos has pretty much answered that one for you

4) It's about the same age as the Earth and much less than the age of the global cluster, the problem is obvious.
 
  • #4
yes it is clear i made a fatal error. in case of problem 1 a)if the density of the universe is lower than the critical value...

Now the universe will keep expanding...I think that the end of the universe won't be different in both cases.When I asked for a hint about the question to the assistant he told me to think as escape velocity.So what happens? If you send a rocket with a speed equal to the escape velocity of greater than that, the rocket will leave the planet?


And in the last question what I really want to learn is "what was the problem Hubble faced"?
 
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  • #5
1) a) becomes the universe will contiune to expand forever (look-up heat death)

4) the problem as I said is obvious, his value for the age of the universe was in disagreement with other values.
 

What is the expansion of the universe?

The expansion of the universe is the theory that the universe is constantly expanding and that the distance between galaxies and other celestial bodies is increasing over time. This expansion is supported by observations of redshift in the light from distant galaxies.

What is causing the expansion of the universe?

The exact cause of the expansion of the universe is still a topic of debate among scientists. One theory is that it is due to the presence of dark energy, a mysterious force that counteracts the force of gravity and causes the universe to expand at an accelerating rate.

How fast is the universe expanding?

The rate of expansion of the universe is measured by the Hubble constant, which is currently estimated to be around 70 km/s per megaparsec. This means that for every 1 million parsecs (3.26 million light years) of distance, the universe is expanding at a rate of 70 kilometers per second.

Will the expansion of the universe ever stop?

Based on current observations and theories, it is believed that the expansion of the universe will continue indefinitely. However, the rate of expansion may change over time depending on the amount of dark energy present in the universe.

What is the significance of the expansion of the universe?

The expansion of the universe has significant implications for our understanding of the origins and fate of the universe. It also plays a crucial role in the formation and evolution of galaxies and other celestial bodies. Studying the expansion of the universe can also provide insights into the nature of dark energy and other fundamental forces in the universe.

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