What is the Difference Between Motion and Expansion in the Hubble Law?

In summary, the two students are discussing their understanding of Hubble's Law. Student 1 believes that the space is expanding, making our galaxy bigger. Student 2 argues that our galaxy is a gravitationally bound system, so it is not getting bigger but rather moving at greater speeds. Both students have valid points, but it is important to understand the distinction between expansion and motion. Further research on the topic may help in understanding the differences between the two.
  • #1
itsirk2008
6
0
Can anyone help me with this question? Or at least lead me in the right direction?

Two students are having a discussion after studying the Hubble Law.

Student 1: According to the Hubble Law space is expanding. Therefore our galaxy is bigger today than it was in the past and will keep getting bigger.

Student 2: No. Our galaxy is a gravitationally bound system. So it is not getting bigger but it is moving at greater speeds as it ages.

Which student do you agree with? Discuss why you agree or disagree with either or both of them.
 
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  • #2
Another Astronomy Question

I need help with this one also...

Student 1: According to the Hubble Law space is expanding. This means that other galaxies are moving away from us. So our galaxy will never collide with the Andromeda Galaxy.

Student 2: All galaxies have their own intrinsic motions. Since the Hubble flow is constant, all those galaxies that are moving towards us will collide with our galaxy sooner or later.

Which student do you agree with? Discuss which parts of their statements you agree or disagree with and explain your reasoning.
 
  • #3
We don't spoonfeed here, but we're happy to help. What are your thoughts?
 
  • #4
Was not looking for spoonfeeding...that won't get me anywhere in the long run?

As far as student # 1, I agree with the statement that according to Hubble Law, the space is expanding. But expanding does not necessarily mean bigger.
 
  • #5
I also know from my reading that the space between our galaxies is expanding; the farther a galaxy is, the faster it is going.
 
  • #6
Need homework help - Hubble Law

Can anyone help me with this question? Or at least lead me in the right direction?

Two students are having a discussion after studying the Hubble Law.

Student 1: According to the Hubble Law space is expanding. Therefore our galaxy is bigger today than it was in the past and will keep getting bigger.

Student 2: No. Our galaxy is a gravitationally bound system. So it is not getting bigger but it is moving at greater speeds as it ages.

Which student do you agree with? Discuss why you agree or disagree with either or both of them.
 
  • #7
...and I agree with student # 2 when he/she says that our galaxy is a gravitationally bound system.
 
  • #8
1] Galaxies are indeed gravitationally bound.

As for #2. The velocity of Andromeda wrt to Milky Way is actually well-known and pretty much nails the answer.
 
  • #9


itsirk2008 said:
Can anyone help me with this question? Or at least lead me in the right direction?

Two students are having a discussion after studying the Hubble Law.

Student 1: According to the Hubble Law space is expanding. Therefore our galaxy is bigger today than it was in the past and will keep getting bigger.

Student 2: No. Our galaxy is a gravitationally bound system. So it is not getting bigger but it is moving at greater speeds as it ages.

Which student do you agree with? Discuss why you agree or disagree with either or both of them.

I would like to help you understand Hubble law better. But our rule is we don't give anybody answers to homework. Also there is a homework help section of the forum where people are skilled in getting you to think and come up with the answer yourself. They could handle this. Personally I can't figure out how I can help you without giving away the answer.

BTW I notice from the way the problem is worded that you don't have to choose one and say that one is right and the other is wrong. You can, if you want, disagree with both. The key thing will be your discussion. It looks like a multiple choice question where you pick the right answer, but it is really a discussion question. That is my take on it. You better go to Homework Help section with this.

Try this:
https://www.physicsforums.com/forumdisplay.php?f=153
 
  • #10
Threads merged and moved to homework.
 
  • #11
What might help you is if you did some research on the differences between motion and expansion. Expansion, as in Hubble's law, refers to space time whereas the motion within that expansion (galaxies etc...) is bound by c.


hope this helps
 

Related to What is the Difference Between Motion and Expansion in the Hubble Law?

1. What is Hubble's Law in astronomy?

Hubble's Law is a fundamental concept in astronomy that states that the farther a galaxy is from Earth, the faster it is moving away from us. This law is based on the observation that galaxies further away from us have a greater redshift, indicating that they are moving away at a faster rate.

2. Who discovered Hubble's Law?

Hubble's Law is named after American astronomer Edwin Hubble, who first proposed the concept in 1929. However, Hubble's Law was actually first discovered by Belgian astronomer Georges Lemaître in 1927, although his work was not widely known at the time.

3. What is the significance of Hubble's Law?

Hubble's Law provides evidence for the expansion of the universe. It also led to the development of the Big Bang Theory, which states that the universe began as a single point and has been expanding ever since. Hubble's Law also allows us to estimate the age of the universe.

4. How is Hubble's Law used in astronomy?

Hubble's Law is used to measure the distances between galaxies and calculate their velocities. This information can then be used to create a Hubble diagram, which shows the relationship between the distance of a galaxy and its velocity. This can help us better understand the structure and evolution of the universe.

5. Is Hubble's Law still valid today?

While Hubble's Law has been refined and expanded upon over the years, it is still considered a valid and important concept in astronomy. In fact, recent studies have provided even more evidence for the expansion of the universe and the accuracy of Hubble's Law.

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