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#1 Paul's Here

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Posted 18 November 2012 - 11:16 AM

Most distant galaxy found.


Does anyone understand this? How can light from 13.7 billion years ago reach earth "here" if we weren't "here" 13.7 billion years ago? Since "we" and this distant galaxy started out in the same "place," the big bang, around 14 billion years ago, how did we get "here" and the oldest galaxy get "there"?
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#2 PhilO

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Posted 18 November 2012 - 02:25 PM

Well, taking the "big bang" stuff at face value (I don't), you could imagine the classic 2d analog to the 3d situation: starting with a deflated balloon (imagine a very small but very flexible sphere) where everything-that-is, is in very close proximity. Start to blow up the balloon and eventually points on the surface will be various distances apart; at most, the diameter of the balloon apart at any given time. This would be analogous to the 3d case of "expanding space".

A good question though: how would light be travelling between distant points, then? If space is expanding, that effectively adds to the distance that light has to travel, all the time. If it were expanding faster than light, then we would never have knowledge of that part of space; light couldn't outrun it, and no ship we could build, short of FTL capability, would be able to catch up either.

If a photon from that galaxy has actually been travelling for 13.7 billion years (which is gauged by the Hubble redshift of the photon, making further assumptions), and the galaxy is purportedly "very young", it's hard to imagine any implication other than the idea that the "big bang" actually "expanded space" far faster than light speed, but then slowed or stopped. Then the early matter of the universe would be evolving steadily throughout the universe at the "same time". Photons emitted from the galaxy 13.7 billion light years away would take that long to reach us.

However, the very existence of the redshift would seem to imply that the expansion is ongoing; unless they were redshifted during the period of expansion and thus had a "memory" of something that's now over.

If the expansion were ongoing, then light would have to be traversing longer and longer distances to reach us, the further away it originated. The implication from that would seem to be that the things we see at a certain "distance" away would actually be younger than we thought.

I don't buy the big-bang idea, but it's clear that something is going on across cosmological distances that needs a coherent explanation.
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#3 Joss Delage

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Posted 18 November 2012 - 02:31 PM

I'm no physicist, so I'm way out of my depth here. However, isn't it possible that .5b years ago the universe was expanding at a significant % of c? Therefore, as a photon was traveling towards us at speed c, the distance it would have too travel would increase. Also, the universe was much denser then. It's possible that the average speed of light was less then simply because there was less true vaccuum.
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#4 ruveyn ben yosef

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Posted 18 November 2012 - 02:35 PM

I'm no physicist, so I'm way out of my depth here. However, isn't it possible that .5b years ago the universe was expanding at a significant % of c? Therefore, as a photon was traveling towards us at speed c, the distance it would have too travel would increase. Also, the universe was much denser then. It's possible that the average speed of light was less then simply because there was less true vaccuum.


According to Guth's (expansionist) modification of the big bang the cosmos was opaque to light for the first 300,000,000 years until things cooled down enough for energy to condense in to matter which became sparse enough to permit photons to travel more freely.

Prior to that a photon did not have a free path. It is somewhat like that which happens in the Sun. It takes about 100,000 years for a photon to make it to the out layers of the sun. After which it takes 8 min. for the photon to get to Earth. Actually when photons collide with other particles they are absorbed when the collided with particle is bumped up a quantum energy state and then falls down again a photon is re-emitted. So it is really the great grand children of the core emitted photon that makes it to the sun's surface.

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#5 PhilO

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Posted 18 November 2012 - 03:22 PM

To elaborate a little via the 2d spherical analogy: imagine that you had a number of discrete sources on the surface which emitted ink lines at a rate of say one millimeter/hour, radically outwards. This is analogous to light travelling on the surface of the sphere, where the "speed of light" is one millimeter/hour in this analogy.

If the balloon is steadily expanding, the time it takes for a given line to reach another source will be longer and longer as a function of the original distance away and the expansion rate. If the balloon is exactly spherical, each line would eventually traverse a great circle and come back to the starting point (if not otherwise affected along the way) - a distance of 2*pi*r, r=balloon radius.

If the lines grow at a rate of v, then it would take 2*pi*r/v time to traverse the entire circle. It would thus take (2*pi*r/v) * (theta/(2*pi)) time (simplifying to theta*r/v) for the line to connect any two sources, where theta is the minimum angular separation in radians (a maximum of pi radians).

The situation is different if the balloon is expanding. If for example the radius is expanding at a constant rate, then r=r0+u*t, where r0 is the initial radius and u is the expansion rate.

This changes the situation. The effective distance between any two sources becomes theta*r(t)/v = theta*(r0+u*t), or a function dependent both on time and the radius of the balloon at the time you start tracking the line growth from a source.

A simple equation can then be set up to determine the time it would then take for lines to grow between two sources:

v*t = theta*(r0+u*t)

where, to summarize, v=constant speed of lines (light), r0=balloon radius at start of emission, u=constant growth rate of the ballon radius, theta=constant angular separation of two points. Solving for t (the time it will take for a line to grow to reach the two points) we get:

t = r0*theta/(v-u*theta)

Note that t grows to infinity as u*theta approaches v, and becomes infinite when v=u*theta. This is directly analogous to space expanding "at light speed", or beyond.

One of the points I wanted to make here is that the measurement of elapsed "light travel time", t, will vary as r0 and u varies, even for two points that might have been created at a common point in time, so if the "expansion of the universe" were steadily occurring, gauging how "old" something is relative to yourself "in the present time" will be off, and it will be off by different amounts for varying distances (analogous to varying thetas). If u=0 (non-expanding balloon/universe) then that is no longer true, because the u*theta term vanishes in the denominator.

I'm doing this rather quickly, so hopefully I haven't made a glaring error in reasoning somewhere. Interesting stuff, thanks for the question, Paul.
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#6 PhilO

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Posted 18 November 2012 - 03:30 PM

Typo. The above

"The effective distance between any two sources becomes theta*r(t)/v = theta*(r0+u*t)"
should be

"The effective distance between any two sources becomes theta*r(t) = theta*(r0+u*t)"
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#7 Paul's Here

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Posted 18 November 2012 - 04:43 PM

Thanks for your repsonses. The only thing that makes any sense to me is that at some point the two galaxies must have moved apart at a speed faster than the speed of light (how much greater and for how long is not important here). Otherwise, there would be no way for 13 billion year old light to be coming from a location 13 billion light years away. I think that Ruveyn's comment is interesting, however, 300 million years is a pimple on the time scale of 13 billion years. At some point after 300 million years, the two galaxies were far enough apart for photos to flow between them at the normal speed of light. At that point, the light from the first galaxy would be well past us and the light we would be "seeing" throught the next 13 billion - 300 million years would be just as old as our galaxy. There should be no way to get 13 billion year old light to us from the original galaxy. The light reaching us should be from a galaxy that is 13 billion years old, not light from the orginial galaxy as it was 13 billion years ago.
ANTHEM
"It is my eyes which see,
and the sight of my eyes grants beauty to the earth.


It is my ears which hear,
and the hearing of my ears gives its song to the world.


It is my mind which thinks,
and the judgment of my mind is the only searchlight that can find the truth."


---------

"Life, if well spent, is long." - Leonardo

--------------------
(Avatar shows the Milky Way and our place in it.)

#8 Carlos

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Posted 18 November 2012 - 11:43 PM

Most distant galaxy found.


Does anyone understand this? How can light from 13.7 billion years ago reach earth "here" if we weren't "here" 13.7 billion years ago? Since "we" and this distant galaxy started out in the same "place," the big bang, around 14 billion years ago, how did we get "here" and the oldest galaxy get "there"?


It's only confounding and in need of explanation if you buy into the popular creation myth that is The Big Bang.

#9 Arnold

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Posted 18 November 2012 - 11:43 PM

Has the effect of gravity changes had an effect on the speed of light? My understanding is that time measurement is related to the speed of light, and that the speed of light is affected by gravity. Besides this the very concept of 'size' when it relates to the universe seems meaningless; what does one measure it with?

#10 Betsy Speicher

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Posted 19 November 2012 - 04:51 AM

Has the effect of gravity changes had an effect on the speed of light? My understanding is that time measurement is related to the speed of light, and that the speed of light is affected by gravity. Besides this the very concept of 'size' when it relates to the universe seems meaningless; what does one measure it with?


Stephen was involved with the famous Kopeikin-Fomalont experiment to measure the speed of gravity (link) (link). As I understand it, that experiment showed the speed of gravity to be the same as the speed of light as predicted by Einstein.

Perhaps you are thinking of how gravity can deflect and "bend" the movement of light particles?
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#11 ewv

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Posted 19 November 2012 - 06:16 AM

Thanks for your repsonses. The only thing that makes any sense to me is that at some point the two galaxies must have moved apart at a speed faster than the speed of light (how much greater and for how long is not important here). Otherwise, there would be no way for 13 billion year old light to be coming from a location 13 billion light years away. I think that Ruveyn's comment is interesting, however, 300 million years is a pimple on the time scale of 13 billion years. At some point after 300 million years, the two galaxies were far enough apart for photos to flow between them at the normal speed of light. At that point, the light from the first galaxy would be well past us and the light we would be "seeing" throught the next 13 billion - 300 million years would be just as old as our galaxy. There should be no way to get 13 billion year old light to us from the original galaxy. The light reaching us should be from a galaxy that is 13 billion years old, not light from the orginial galaxy as it was 13 billion years ago.


With the most simple assumptions this is a simple algebra problem. They said it is light that originated at the other galaxy t1=420 million years old and it reached us t2 =13.3 billion years later, for a total life of the universe of t1 + t2 = .4 + 13.3 = 13.7 billion years.

The light arriving now would show what the other Galaxy looked like when it was t1 years old, t2 years ago. The galaxies have been moving for the age of the universe t1+t2, the light left at time t1, and traveled for time t2.

If both galaxies have been moving at the same constant speed of v in opposite directions, then we were a distance 2vt1 apart when the light left. We moved vt2 farther while the light was traveling until it caught up with us, so if all the measurements are with respect to the same reference frame, then the distance the light traveled is 2vt1 + vt2 = ct2, so v/c = t2/(2t1 + t2) < 1, not faster then the speed of light.

...................................................-------------------------ct2--------------------------->
.............................................................................................light


<-----------vt2-------------<----vt1------|----vt1---->-----------vt2------------->
..Galaxyother..........................................................................................................Galaxyus

#12 ruveyn ben yosef

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Posted 06 December 2012 - 12:00 AM

You might find this paper on the speed of gravitation interesting:

http://www.msnbc.msn...n/#.UL_fBNuF_9I

The experiment apparently shows Einstein's position that gravitation travels at light speed is correct.

ruveyn

#13 Betsy Speicher

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Posted 06 December 2012 - 06:49 AM

You might find this paper on the speed of gravitation interesting:

http://www.msnbc.msn...n/#.UL_fBNuF_9I

The experiment apparently shows Einstein's position that gravitation travels at light speed is correct.


That was the experiment Stephen was involved with. When the experimenters, Kopeikin and Fomalont, came to California, they came to our house and we spent the day together.

Attached File  sergeivisit2.JPG   460.64KB   0 downloads

In this picture, left to right, Ed Fomalont, Stephen, Sergei Kopeikin. (I took the picture.)
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#14 ruveyn ben yosef

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Posted 06 December 2012 - 12:55 PM

I only dream of having guests like these.

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