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  #31 (permalink)  
Old 27-April-2008, 01:10 AM
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Originally Posted by speedfreek View Post
From Ned Wrights Cosmology FAQ

Is the Universe expanding or is it just that our definitions of length and time are changing?

The definitions of length and time are not changing in the standard model. The second is still 9192631770 cycles of a Cesium atomic clock and the meter is still the distance light travels in 9192631770/299792458 cycles of a Cesium atomic clock.
Did anyone claim otherwise?
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  #32 (permalink)  
Old 27-April-2008, 01:20 AM
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Originally Posted by tommac View Post
Quote:
Originally Posted by speedfreek
Meters don't expand, the universe expands causing spaces to contain more meters.
You have such a great post then end it with this piece of utter nonsense
No. It is not nonsense.
It is the answer to the question you repeatedly keep asking over and over and that Grant Hutchison and others have repeatedly answered over and over and that you keep rejecting without grounds- by having adopted your lack of or mis-understanding as a belief.

This is why you have been driving me up the wall.
  #33 (permalink)  
Old 27-April-2008, 01:22 AM
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Originally Posted by tommac View Post
Did anyone claim otherwise?
Yes.
You have.
Repeatedly claiming that Time must expand if Space expands.

I'm just curious- are you really forgetful or are you having as much trouble keeping up with your many posts, threads and questions as I am considering how scattered they seem to be...?
  #34 (permalink)  
Old 27-April-2008, 01:24 AM
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Originally Posted by Neverfly View Post
Yes.
You have.
Repeatedly claiming that Time must expand if Space expands.

I'm just curious- are you really forgetful or are you having as much trouble keeping up with your many posts, threads and questions as I am considering how scattered they seem to be...?
No sorry it wasnt I ... a second stays a second and a meter stays a meter.
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  #35 (permalink)  
Old 27-April-2008, 01:27 AM
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Originally Posted by tommac View Post
No sorry it wasnt I ... a second stays a second and a meter stays a meter.








OK!
My brain's blown a fuse.
I'm going to get a Dr pepper. See ya later...
  #36 (permalink)  
Old 27-April-2008, 01:35 AM
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Originally Posted by Neverfly View Post








OK!
My brain's blown a fuse.
I'm going to get a Dr pepper. See ya later...

You may be referring to my compression factor post .... but even there a second is a second and a meter a meter ...
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  #37 (permalink)  
Old 27-April-2008, 10:18 AM
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I am simply trying to explain the scientific method, the invariance that is, by definition, required for a frame of reference, and you cannot seem to make sense of it. But it is not nonsense. Did you not read that last post?

"The definitions of length and time are not changing in the standard model."

The universe expands and so distances increase. 1 lightyear does not become a larger lightyear as time goes on. 1 meter does not become a larger meter as time goes on. Lightyears (and therefore meters) are, and always have been, the same length. Lightyears (and therefore meters) do not expand with the universe, distances increase with the expansion.

You start off with 100,000,000 meters and you end up with 200,000,000 meters if the universe doubles in size. Did the universe expand? Yes. Did the distance in between objects increase? Yes. Did a meter expand? No, it stayed as a meter and the number of meters increases with the expansion. More meters are introduced by the expansion. If you want to think of it as space stretching, then what was once 1 meter has now stretched to become 2 meters. You now have more meters. What part of this very simple principle do you not understand?

(This is what happens when people say things like "Meter sticks grow longer relative to the past as space expands while clocks simultaneously run faster", we have to be very careful with terminology - I myself said something similar in another post and regret it ever since!)
  #38 (permalink)  
Old 28-April-2008, 06:31 AM
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Quote:
Originally Posted by Neverfly View Post
Yes.
You have.
Repeatedly claiming that Time must expand if Space expands.

I'm just curious- are you really forgetful or are you having as much trouble keeping up with your many posts, threads and questions as I am considering how scattered they seem to be...?
This thread has been impossible to follow so could someone define what the issue is? Tommac said in the OP that time must expand if space expands and I thought that was the topic of discussion. As I see it, time quickens as space expands and this is why some values defined as distance divided by time are able to remain unchanged. Einstein’s c, light years, and meters are three things that remain the same if, and only if, time "expands" (clocks tick faster) as space expands.
Quote:
Originally Posted by speedfreek View Post
If you want to think of it as space stretching, then what was once 1 meter has now stretched to become 2 meters. You now have more meters. What part of this very simple principle do you not understand?
I don’t understand how stretching space can make two meters from one unless time expands (quickens, runs faster, however…) as space expands. Our clocks tell us that it now takes light twice as long to get from point A to point B when space stretches from one meter to two. Either our clocks are running faster or our light is moving slower. The length of a meter is defined as the distance light can travel in a given length of time so, if c is a constant, then the difference must be in the clocks.
  #39 (permalink)  
Old 28-April-2008, 11:11 AM
grant hutchison grant hutchison is offline
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Originally Posted by Bob Angstrom View Post
Our clocks tell us that it now takes light twice as long to get from point A to point B when space stretches from one meter to two. Either our clocks are running faster or our light is moving slower. The length of a meter is defined as the distance light can travel in a given length of time so, if c is a constant, then the difference must be in the clocks.
No, the difference is in the distance: it takes twice as long to cover twice the distance at the same velocity.
If you drive at the (UK) speed limit to a town 70 miles away and it takes an hour, you'll be unsurprised when it takes two hours at the same speed to reach a town 140 miles away. You won't blame your watch or your car, you'll blame the distance.
Why do you think light will behave any differently?

Grant Hutchison
  #40 (permalink)  
Old 28-April-2008, 01:58 PM
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Originally Posted by grant hutchison View Post
No, the difference is in the distance: it takes twice as long to cover twice the distance at the same velocity.
If you drive at the (UK) speed limit to a town 70 miles away and it takes an hour, you'll be unsurprised when it takes two hours at the same speed to reach a town 140 miles away. You won't blame your watch or your car, you'll blame the distance.
Why do you think light will behave any differently?

Grant Hutchison
In other words the space-time fairy drops two kilos of space in when needed for calculation deficiencies.
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  #41 (permalink)  
Old 28-April-2008, 02:05 PM
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Originally Posted by tommac View Post
In other words the space-time fairy drops two kilos of space in when needed for calculation deficiencies.
Not for calculation deficiencies, no. That's putting the cart before the horse.
But more space appears: you can imagine existing space stretching, you can imagine new space "welling up" from an unknown source, you can even imagine space-time fairies if you really want to.
All the mathematical description of the expanding universe tells us is that the distance increases, so light takes longer to cross it. That's all there is to it. You might as well get used to the idea, to quote Pat Benatar.

Grant Hutchison
  #42 (permalink)  
Old 28-April-2008, 02:22 PM
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Originally Posted by grant hutchison View Post
Not for calculation deficiencies, no. That's putting the cart before the horse.
But more space appears: you can imagine existing space stretching, you can imagine new space "welling up" from an unknown source, you can even imagine space-time fairies if you really want to.
All the mathematical description of the expanding universe tells us is that the distance increases, so light takes longer to cross it. That's all there is to it. You might as well get used to the idea, to quote Pat Benatar.

Grant Hutchison
Again, how can one proove what you are saying ( #1 ) vs what I am saying (#2) in fact what I am saying seems also to be similar to the effects we see near a gravitational well. If you take the compression of space ( kind ofthe opposite to what you are saying ) that would mean that the space fairy comes and takes back the space. The difference between what you are saying and what I am saying is somewhat subtle and I believe it would be hard to prove which one is right ... however with the way I am explaining it I think the opposite can be seen and measured in nature.
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  #43 (permalink)  
Old 28-April-2008, 02:35 PM
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Originally Posted by tommac View Post
Again, how can one proove what you are saying ( #1 ) vs what I am saying (#2)
To be honest, I don't have the foggiest notion what you are saying. Your #2 seems to require someone to stand outside the universe with an extra-universal metre-stick, which isn't a great starting point for reasoned discussion.

Quote:
Originally Posted by tommac View Post
... in fact what I am saying seems also to be similar to the effects we see near a gravitational well. If you take the compression of space ( kind ofthe opposite to what you are saying ) that would mean that the space fairy comes and takes back the space
"Compression" is your word for what happens under gravity, and it's misleading. Others (Richard, I believe) have pointed out that there is a distortion of the spacetime coordinate system under gravity, which is mathematically well described and experimentally well tested.

Grant Hutchison
  #44 (permalink)  
Old 28-April-2008, 05:35 PM
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Originally Posted by grant hutchison View Post
"Compression" is your word for what happens under gravity, and it's misleading. Others (Richard, I believe) have pointed out that there is a distortion of the spacetime coordinate system under gravity, which is mathematically well described and experimentally well tested.

Grant Hutchison
The changes involved as the universe expands include a decline in gravitational density of the sort described in general relativity which uses Einstein’s c as an absolute. Any gravitational distortion of the space-time coordinate system involves changes in both space and time. As space expands, time accelerates. We don’t have an-extra universal meter-stick or a god’s eye view of the universe to tell us if space is expanding. Our observations are internally grounded in the use of light and clocks to measure distance. Tommac may not have the correct terminology but he has the right idea when he says that the expansion of space requires the expansion of time if c is to remain a constant.
  #45 (permalink)  
Old 28-April-2008, 06:01 PM
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Tommac may not have the correct terminology but he has the right idea when he says that the expansion of space requires the expansion of time if c is to remain a constant.
No, he doesn't, for reasons that have been explained repeatedly. The actual FLRW models include a space expansion but not a time expansion. This causes no problems for the speed of light, since the light simply takes longer to travel the increased distances involved. There's simply no "requirement" about it, and it's difficult to see why anyone would think there was.

Grant Hutchison
  #46 (permalink)  
Old 28-April-2008, 07:11 PM
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Originally Posted by grant hutchison View Post
No, he doesn't, for reasons that have been explained repeatedly. The actual FLRW models include a space expansion but not a time expansion. This causes no problems for the speed of light, since the light simply takes longer to travel the increased distances involved. There's simply no "requirement" about it, and it's difficult to see why anyone would think there was.

Grant Hutchison
A quick question as a thought experiment Grant

If a beam of light was traveling through space and reached a part of space that was expanding at C would that light be deemed to be traveling no distance, but taking infinite time or would it be deemed fixed at that spot? looking at it from 3 perspectives- away from the observer, towards the observer, adjacent to the observer? I guess this is really a SR, Question
  #47 (permalink)  
Old 28-April-2008, 07:43 PM
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Originally Posted by cosmocrazy View Post
A quick question as a thought experiment Grant

If a beam of light was traveling through space and reached a part of space that was expanding at C would that light be deemed to be traveling no distance, but taking infinite time or would it be deemed fixed at that spot? looking at it from 3 perspectives- away from the observer, towards the observer, adjacent to the observer?
This stuff's going on all the time in the expanding universe model.
Cosmic microwave background photons, for instance, started off in our direction 13.7 billion years ago, from a proper distance of about 40 million lightyears, in a region of space that was moving away from us at 50 times lightspeed. So those photons were propagating at lightspeed in their own frame, but were moving away from us (in terms of proper distance) at 49 times lightspeed.
But the expansion of space was slowing, and the photons were propagating constantly into regions that were receding from us more slowly than their point of departure. So eventually they arrived in a region that was moving away from us at lightspeed. As viewed from their emission point, they were receding at some multiple of lightspeed, because the emission point was expanding away from their current location. As viewed from their local space, they were moving at lightspeed. As viewed from our location, they were making no progress towards us.
That's a temporary state of affairs, though, because they continued to propagate into regions of space that were moving more slowly relative to us, and so they began to make progress towards us, until they eventually arrived (at lightspeed) in our local space.

Grant Hutchison
  #48 (permalink)  
Old 28-April-2008, 08:13 PM
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Thanks Grant makes good sense!
  #49 (permalink)  
Old 28-April-2008, 08:35 PM
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This stuff's going on all the time in the expanding universe model.
a region of space that was moving away from us at 50 times light speed. So those photons were propagating at light speed in their own frame, but were moving away from us (in terms of proper distance) at 49 times light speed.
How would this be measured in time? relative to us and the photons?
I realize that the original 40 million light years took 13.7 billion but at greater than light speed how would we determine the time dilation and length contraction? how would this be applied to space-time?
  #50 (permalink)  
Old 28-April-2008, 08:46 PM
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