Something I don't understand about astronomy and distance to objects.
Post Reply
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
07-04-2013, 07:24 PM
RE: Something I don't understand about astronomy and distance to objects.
I'll have to give those vids a go tomorrow. It's just about bed time for me since I have to wake up at like 4 am.

“Whenever you find yourself on the side of the majority, it's time to pause and reflect.”

-Mark Twain
Find all posts by this user
Like Post Quote this message in a reply
07-04-2013, 07:33 PM
RE: Something I don't understand about astronomy and distance to objects.
Yuk - 4am. What are you up to these days GT?

A new type of thinking is essential if mankind is to survive and move to higher levels. ~ Albert Einstein
Find all posts by this user
Like Post Quote this message in a reply
09-04-2013, 10:24 PM
RE: Something I don't understand about astronomy and distance to objects.
Now, I didn't watch all the videos, but hmmm. That's an awesome question. My first answer is that 'distance' as such doesn't really mean anything in that cosmological context.

My second answer is a bit longer.

How we measure 'distance' (insofar as there is such a thing and insofar as there would be a single one even if there were) is actually pretty simple. We assume certain types of objects (such as the 1A supernovae mentioned) are of a uniform brightness. Therefore, the farther away they are, the dimmer they are. We can check the distances by other means for closer objects (by parallax or something, there's a few different methods) and that is then extrapolated for farther away objects.

So, what that actually measures is how far the light has travelled from emission to detection here on earth in the present (insofar as there is a here and a present - isn't relativity fun?). So, that neatly explains why we also say things are x years old interchangeably with x distance away: what we observe is a photon that we calculate has travelled y light years, and at the speed of light, that means it took y years to do it! Well, insofar as one can say it 'took' any amount of time - okay, I'll stop that.

Redshift is a different thing; that measures, in the simplest sense, how an object is moving (well, was moving, at the time it emitted whatever we're now seeing). That's the doppler effect, which you'll recognize if you've ever heard a car go past! A source moving towards you has its frequency raised (so light gets bluer), and a source moving away seems to have a lower frequency (light gets redder). Nearly everything, cosmologically, is moving away - hence, redshifted.

To tie it all together - what Hubble did, back in the 1920s, was compare the two sets of data. He found that objects that were farther away were also more redshifted - they were moving away faster than closer objects were. The data were very well correlated, and via a very simple relation at that. To account for such mathematics, the universe would have to be expanding!

Fair warning: I'm not an astrophysicist either. Well, not an astrophysicist, anyway...
Find all posts by this user
Like Post Quote this message in a reply
[+] 3 users Like cjlr's post
11-04-2013, 03:06 AM
RE: Something I don't understand about astronomy and distance to objects.
I really missed some brain food. Thanx for this, I 'm gonna ponder it in my head for days.

[Image: a6505fe8.jpg]
I have a theory that the truth is never told during the nine-to-five hours.
-Hunter S. Thompson
Find all posts by this user
Like Post Quote this message in a reply
13-04-2013, 07:11 AM
RE: Something I don't understand about astronomy and distance to objects.
Hey, Germany.

I am NOT a physicist. So take this with a grain of salt.

Redshift measures how the light has been stretched BY the expansion of the universe. The star isn't moving away from us in the sense that a baseball moves away from your hand when you throw it. It's moving away from us because the universe itself is expanding. It occupies the same position in space (more or less, galaxies do attract to one another gravitationally) but it is the space itself that is moving. That is to say, when the baseball leaves your hand, your position in space and its position space remain the same, but the space between your hand and the ball expands. Said differently, blow up a balloon. Put two dots on the surface with a marker. Then blow it up some more. The dots occupy the same position on the balloon, but the balloon expanded.

Here's the fucked part.

We just time traveled.

The idea of linear time is annihilated by the fact that NOW does not exist in any absolute sense. What we see of that star/supernova, is what happened 10 billion years ago as far as we're concerned. In seeing it, we have time traveled 10 billion years. That is to say, we are seeing the star's then in our now. Their then is occurring in our now. Here's Brian Greene on that subject:





Hope this helps.

Peace and Love and Empathy,

Matt
Find all posts by this user
Like Post Quote this message in a reply
13-04-2013, 12:48 PM
RE: Something I don't understand about astronomy and distance to objects.
(13-04-2013 07:11 AM)Ghost Wrote:  Hey, Germany.

I am NOT a physicist. So take this with a grain of salt.

Redshift measures how the light has been stretched BY the expansion of the universe. The star isn't moving away from us in the sense that a baseball moves away from your hand when you throw it. It's moving away from us because the universe itself is expanding. It occupies the same position in space (more or less, galaxies do attract to one another gravitationally) but it is the space itself that is moving. That is to say, when the baseball leaves your hand, your position in space and its position space remain the same, but the space between your hand and the ball expands. Said differently, blow up a balloon. Put two dots on the surface with a marker. Then blow it up some more. The dots occupy the same position on the balloon, but the balloon expanded.

Here's the fucked part.

We just time traveled.

The idea of linear time is annihilated by the fact that NOW does not exist in any absolute sense. What we see of that star/supernova, is what happened 10 billion years ago as far as we're concerned. In seeing it, we have time traveled 10 billion years. That is to say, we are seeing the star's then in our now. Their then is occurring in our now. Here's Brian Greene on that subject:





Hope this helps.

Peace and Love and Empathy,

Matt

I don't think you are entirely correct about time.

Suppose there is empty space. Place into that space two unmoving synchronized clocks. Now expand the space between those clocks. They would forever keep the same time no matter how much space expands. However if you set one of the clocks in motion then they would lose synchronization. The further away the clocks are from each other the more unsynchronized they would become for a given amount of motion.
Find all posts by this user
Like Post Quote this message in a reply
13-04-2013, 01:18 PM
RE: Something I don't understand about astronomy and distance to objects.
(13-04-2013 12:48 PM)Heywood Jahblome Wrote:  
(13-04-2013 07:11 AM)Ghost Wrote:  Hey, Germany.

I am NOT a physicist. So take this with a grain of salt.

Redshift measures how the light has been stretched BY the expansion of the universe. The star isn't moving away from us in the sense that a baseball moves away from your hand when you throw it. It's moving away from us because the universe itself is expanding. It occupies the same position in space (more or less, galaxies do attract to one another gravitationally) but it is the space itself that is moving. That is to say, when the baseball leaves your hand, your position in space and its position space remain the same, but the space between your hand and the ball expands. Said differently, blow up a balloon. Put two dots on the surface with a marker. Then blow it up some more. The dots occupy the same position on the balloon, but the balloon expanded.

Here's the fucked part.

We just time traveled.

The idea of linear time is annihilated by the fact that NOW does not exist in any absolute sense. What we see of that star/supernova, is what happened 10 billion years ago as far as we're concerned. In seeing it, we have time traveled 10 billion years. That is to say, we are seeing the star's then in our now. Their then is occurring in our now. Here's Brian Greene on that subject:





Hope this helps.

Peace and Love and Empathy,

Matt

I don't think you are entirely correct about time.

Suppose there is empty space. Place into that space two unmoving synchronized clocks. Now expand the space between those clocks. They would forever keep the same time no matter how much space expands. However if you set one of the clocks in motion then they would lose synchronization. The further away the clocks are from each other the more unsynchronized they would become for a given amount of motion.

That is not correct. As space expands, the two clocks have motion relative to one another. Observers at each clock will see the other clock with a different time. And the difference will be symmetric.

Skepticism is not a position; it is an approach to claims.
Science is not a subject, but a method.
[Image: flagstiny%206.gif]
Visit this user's website Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes Chas's post
13-04-2013, 09:23 PM
RE: Something I don't understand about astronomy and distance to objects.
(13-04-2013 01:18 PM)Chas Wrote:  That is not correct. As space expands, the two clocks have motion relative to one another. Observers at each clock will see the other clock with a different time. And the difference will be symmetric.

Yep. They'd each perceive the other as moving, but neither would claim to have themselves accelerated. Imagine they were sending pulses of light to each other. As the distance increased the frequency would decrease (redshift!). Either observer would see the other getting farther away, and therefore see them as moving away. If you were exactly in between them, and their motion was symmetrical, then you'd get back two identical responses whenever you asked what times they both had (which, though they agreed, would then disagree with whatever clock you've got on your own person).

Motion is simple, after all - it's just a change in displacement over time. Any other object in an expanding universe is farther away each time you check. So, from our point of view, as observers, it totally doesn't matter whether it's self-propelled or being 'carried' by expansion of space-time. Same difference.
Find all posts by this user
Like Post Quote this message in a reply
14-04-2013, 12:36 AM (This post was last modified: 14-04-2013 12:43 AM by Heywood Jahblome.)
RE: Something I don't understand about astronomy and distance to objects.
If space expanded so that the clocks were one light minute apart, an observer at one clock would see the other clock as being 1 minute behind because it would take one minute for the information transmitted from one clock to reach the other. However both clocks would still share the same "now". Suppose you are exactly between the two clocks. If observers at each clock were instructed to send a light pulse to you when they observe a specific time on their clocks, you would receive both light pulses at the same time. The reason for this is because the speed of light is constant and the clocks remain synchronized.

Now let's change the scenario just a little bit. The clocks start out exactly synchronized as before. Suppose space isn't expanding at all but instead one clock is set in motion thru space and travels a distance of one light minute. You happen to be stationed exactly between the two. If the observers at each clock send their light pulses at the designated time, you will observe them arriving at your location not at the same time as in the first scenario, but a different times. The reason for this is because the clocks are no longer synchronized.

When both clocks were stationary in spacetime, all their momentum is expending moving thru just the time dimension. This is true even if the clocks are being carried away from each other by expanding spacetime. However if one clock is set in motion thru spacetime, then some of its motion thru spacetime is taken away from traveling thru the time dimension and instead is used to travel thru spatial dimension. That's why clocks in motion slow down.

Maybe I am wrong but I read Ghost's comments as a claim that the expansion of spacetime was responsible for destroying an absolute now. I don't think that is correct. There is no absolute universal now, but not because spacetime expands. I would re-read my copy of The Fabric of the Cosmos to see exactly what Greene says about it, but I gave it away.
Find all posts by this user
Like Post Quote this message in a reply
14-04-2013, 08:23 AM
RE: Something I don't understand about astronomy and distance to objects.
(14-04-2013 12:36 AM)Heywood Jahblome Wrote:  If space expanded so that the clocks were one light minute apart, an observer at one clock would see the other clock as being 1 minute behind because it would take one minute for the information transmitted from one clock to reach the other. However both clocks would still share the same "now". Suppose you are exactly between the two clocks. If observers at each clock were instructed to send a light pulse to you when they observe a specific time on their clocks, you would receive both light pulses at the same time. The reason for this is because the speed of light is constant and the clocks remain synchronized.

Now let's change the scenario just a little bit. The clocks start out exactly synchronized as before. Suppose space isn't expanding at all but instead one clock is set in motion thru space and travels a distance of one light minute. You happen to be stationed exactly between the two. If the observers at each clock send their light pulses at the designated time, you will observe them arriving at your location not at the same time as in the first scenario, but a different times. The reason for this is because the clocks are no longer synchronized.

When both clocks were stationary in spacetime, all their momentum is expending moving thru just the time dimension. This is true even if the clocks are being carried away from each other by expanding spacetime. However if one clock is set in motion thru spacetime, then some of its motion thru spacetime is taken away from traveling thru the time dimension and instead is used to travel thru spatial dimension. That's why clocks in motion slow down.

Maybe I am wrong but I read Ghost's comments as a claim that the expansion of spacetime was responsible for destroying an absolute now. I don't think that is correct. There is no absolute universal now, but not because spacetime expands. I would re-read my copy of The Fabric of the Cosmos to see exactly what Greene says about it, but I gave it away.

There is no absolute now because there is no privileged frame of reference. All frames of reference are relative to others, negating the possibility of an absolute now.

Skepticism is not a position; it is an approach to claims.
Science is not a subject, but a method.
[Image: flagstiny%206.gif]
Visit this user's website Find all posts by this user
Like Post Quote this message in a reply
[+] 1 user Likes Chas's post
Post Reply
Forum Jump: