What do you mean, an incorrect picture?Peter Watkins said:Thank you for your patience gentlemen, but consider Jock Homo's example, if the photons left their source at the same time then they are all together. Put these on the rubber sheet, stretch it, and they will remain together but their wave forms will be stretched, by factors according to their original length. The unequal starting points produce an incorrect picture.
What? How so?Peter Watkins said:Light beams are made up of photons. It is these photons that describe the wave length.
Light exhibits wave-particle duality. This means that, in come contexts, it acts like a stream of particles and, in other contexts, it acts like a wave. When you're talking about light red-shifting, you're treating it like a wave so that's how you should probably be visualizing it...It is these photons that are moved apart by the supposed expansion of space. If we have two photons, side by side, one from visible light and one from gamma rays, why would one be pulled along at a faster rate than the other? Also, if the light rays really are stretched, by say, 30%, wouldn't this mean that the light is traveling at faster than light speed? Additionally, if the light-waves are stretched, doesn't it make more sense to ascribe this to our rate of recession? Our high rate of separation from the most distant galaxies would produce the effect of stretched light.
|----------| space that's 10 units long
|-----| light wave whose wavelength is 5 units long
|-| light wave whose wavelength is 1 unit long|--------------------| now 20 units long
|----------| now 10 units long
|--| now 2 unit longAhhh, perhaps that's where your confusion lies.Peter Watkins said:I don't want to run the risk of another infraction, but interpretation is in the mind of the reader. The example you show above sees the leading edge of the upper light unit traveling at 5 times the rate of the lower unit.
What? How so? Please let me quote myself:Peter Watkins said:I don't want to run the risk of another infraction, but interpretation is in the mind of the reader. The example you show above sees the leading edge of the upper light unit traveling at 5 times the rate of the lower unit. Carried to it's logical conclusion, if the longer unit took 200 years to arrive here, then the shorter would take a thousand years!
It's good advice. Please heed it...Jocko Homo said:In the future, instead of just saying things hoping that we'll just agree with you, you should try to explain your conclusions (like how is it that photons describe wavelength?). Doing so will allow you to either see for yourself why your arguments don't make sense and avoid posting them in the first place or allow us to follow your correct chain of thought. This greatly helps communication...
Is English your first language? If it isn't, I will make my posts more redundant in the future. Either way, you should make an effort to read my posts (indeed, all posts) more carefully. I'll quote myself again:You say that the red and blue shift are due strictly to movement through space. Haven't we been told, endlessly, that we are not moving through space, but rather, that expanding space is carrying the galaxies apart, and due to this they are exempt from the light speed limit. If this is not the case then there will have to be some serious recalculation of various recession rate tables.
The bold word was previously emphasized using italics. However, because all quoted text is italicized, I've chosen to bold it in the quote...Jocko Homo said:There is a red (and blue) shift due strictly to movement through space, called the Doppler effect. However, there's also a strictly red shifting on everything we look at and this is due to universal expansion...
By your description, it doesn't sound like Marcus disagrees with me...Some while back I posed a very specific question which was; "is the red shift referred to by cosmologist the shift of the absorbtion lines, seen on the spectra of stars and galaxies, toward the red end of the spectrum?" The reply by Marcus was an unequivocal and unqualified "Yes". It is obviously convenient to refer to this as the Doppler effect as it saves explanation. For much of the time that the universe has been viewed through telescopes there has been no colour change and this shift was not a Doppler effect. I realize that the advent of ever better telescopes has probably now seen the true Doppler effect. At what recession rate can this first be seen?
Peter Watkins said:Some while back I posed a very specific question which was; "is the red shift referred to by cosmologist the shift of the absorbtion lines, seen on the spectra of stars and galaxies, toward the red end of the spectrum?" The reply by Marcus was an unequivocal and unqualified "Yes". It is obviously convenient to refer to this as the Doppler effect as it saves explanation. For much of the time that the universe has been viewed through telescopes there has been no colour change and this shift was not a Doppler effect. I realize that the advent of ever better telescopes has probably now seen the true Doppler effect. At what recession rate can this first be seen?
Chalnoth, When a full spectrograph of a distant galaxy is taken, did all the light rays that produced this spectrum leave their source at the same time?
This assertion is wrong according to these peer-reviewed references and authors (among many others):Chalnoth said:It's just that the space is expanding, so that even traveling at the same speed, they end up further apart in the end.
Uh, what? Why do you think any of these articles contradict what I wrote?TrickyDicky said:This assertion is wrong according to these peer-reviewed references and authors (among many others):
Davis, Lineweaver and Webb (2003)
Whiting (2004)
Barnes et al. (2006)
Peacock (2007)
Chodorowski (2007)
Hogg and Bunn (2009)
See for instance:
http://arxiv.org/abs/0808.1081
Personally I'm actually agnostic wrt this concept of "expansion of space". I'll just mention that in order to contend it one logically must consider "space" as something material, an expandible object, a knd of medium or substance, and this is rejected by mainstream science along with all ether theories.
Let me just stop you right there. Expansion isn't a speed. It's a rate. The units are different. Saying that the universe is expanding at faster than the speed of light is like saying that your car's engine revolving at 3000rpm's is faster than 60mph. The statement doesn't even make sense.ptalar said:Basic Problem Statement: If the Universe is expanding at roughly 3 times the speed of light,
Because the rate of expansion is not uniform but has changed over time. Back when the photons we see today were first emitted, our universe was expanding at a much, much higher rate, carrying away the photons moving in our direction at a high speed. Since then, the expansion has slowed, such that eventually those photons started being able to make headway against the expansion. It shouldn't be much of a surprise that the amount of time it took those photons to reach us (13.7 billion years) is between the distance from which those photons were originally emitted (42 million light years) and the distance that matter is away from us today (46 billion light years).ptalar said:Why can we see 46 billion light years away? Remember the actual Universe is about 14 billion years old in absolute time. So in theory we should only be able see 14 billion light years in any direction, not 46 billion light years.
Chalnoth said:Let me just stop you right there. Expansion isn't a speed. It's a rate. The units are different. Saying that the universe is expanding at faster than the speed of light is like saying that your car's engine revolving at 3000rpm's is faster than 60mph. The statement doesn't even make sense.
Because expansion is a rate, there is no sense in which it is either faster or slower than the speed of light. And at any non-zero rate of expansion, there will be objects some distance away that have recession velocities faster than the speed of light. At faster rates of expansion, those objects will be closer.
Because the rate of expansion is not uniform but has changed over time. Back when the photons we see today were first emitted, our universe was expanding at a much, much higher rate, carrying away the photons moving in our direction at a high speed. Since then, the expansion has slowed, such that eventually those photons started being able to make headway against the expansion. It shouldn't be much of a surprise that the amount of time it took those photons to reach us (13.7 billion years) is between the distance from which those photons were originally emitted (42 million light years) and the distance that matter is away from us today (46 billion light years).
Yes, I noticed that. I was trying to say that that reasoning doesn't work. Hopefully the car analogy I used was a sufficiently good engineering example for you to see it. If not, here's another, different analogy that is no less relevant: saying the expansion is faster than the speed of light is like saying that the height of a building is faster than 30m/s. The statement doesn't even make sense.ptalar said:In regard to your first assertion I just made a rough engineering approximation to get a physical feel of what was going on. If the size of the visible Universe is 46 billion light years in all directions and the absolute age of the Universe is 14 billion years then I assumed that the rate of expansion at the leading edge of the Universe(if there is one), as it expands into the bulk, is roughly 3 times the speed of light: 46/14 which is approximately 3. What I think you are really saying is that the expansion of the Universe and the speed of light are not mathematically related. The expansion of the Universe is its own unique algorithim based on dark energy or vacuum energy and the fact that nothing need not conform to any law of physics. I agree. I was just trying to find a physical rationale for the rate of expansion and get a determination of how fast it was expanding in engineering terms.
Sort of. The issue here is that it is not only the redshift that matters, but also how our universe has expanded over time. The redshift only tells us the total amount of expansion since the light was emitted. How fast that expansion occurred over time determines both how far away the object was and how long ago it emitted that light.ptalar said:As far as your second assertion I think I see where you are going. As the Universe expands there is still a trail of light at any given point in the visible Universe. That light is not being stretched. Rather it is just the light at any given distance during the expansion time period of 13.7 billion years. The expansion rate and the speed of light are not related except the distance of a luminous object can be determined by its red shift. The red shifts of the most distant visible objects indicate a 46 billion light year distance in any direction. Am I on the correct thought trail?
Sorry, I had a copy-paste error with the references, actually I'm basically referring to the Chodorowski and Hogg and Bunn ones.Chalnoth said:Uh, what? Why do you think any of these articles contradict what I wrote?
You didn't answer my question.TrickyDicky said:Sorry, I had a copy-paste error with the references, actually I'm basically referring to the Chodorowski and Hogg and Bunn ones.
Chalnoth said:Yes, I noticed that. I was trying to say that that reasoning doesn't work. Hopefully the car analogy I used was a sufficiently good engineering example for you to see it. If not, here's another, different analogy that is no less relevant: saying the expansion is faster than the speed of light is like saying that the height of a building is faster than 30m/s. The statement doesn't even make sense.
Sort of. The issue here is that it is not only the redshift that matters, but also how our universe has expanded over time. The redshift only tells us the total amount of expansion since the light was emitted. How fast that expansion occurred over time determines both how far away the object was and how long ago it emitted that light.
One rough analogy I might use is that of a person driving between two locations. Imagine, if you will, that knowing the redshift is sort of kinda like knowing the origin and destination, e.g. knowing that the person drove from Denver to Chicago. But knowing the origin and destination is not sufficient to know how far the driver went or how long it took to do it: we also need to know how fast the driver was moving, and what specific route the driver took. With a light ray, the speed is, of course, given by the speed of light. But the path the light ray takes is given by how space expands in the intervening time.
To go back to the example of the furthest light we see, that from the Cosmic Microwave Background, that light was emitted a mere 42 million light years away, but because of the expansion of the universe it was forced to take a path towards us that made it take 13.7 billion years. That that stuff that originally emitted that light is now some 46 billion light years away is interesting but incidental.
ptalar said:Basic Problem Statement: If the Universe is expanding at roughly 3 times the speed of light, and the visible Universe is approximately 46 billion light years in any direction. Why can we see 46 billion light years away? Remember the actual Universe is about 14 billion years old in absolute time. So in theory we should only be able see 14 billion light years in any direction, not 46 billion light years.
Explanation: I have no explanation because it would all be empirical and would be considered philosophy. Maybe somebody else has a better explanation.
This part is just wrong, no matter how you slice it. The furthest we can see is the cosmic microwave background, the light from which was emitted about 43 million light years away, but due to the expansion took 13 billion years to get here. The matter that once emitted that light is currently about 46 billion light years away.Naty1 said:but because the universe is expanding as light travels towards us and light therefore takes longer to get here, we can see out about 46B light years. In other words, the oldest light is 46B years old.
...the light from which was emitted about 43 million light years away, but due to the expansion took 13 billion years to get here
If space were not expanding, the most distant object we could see would now be about 14 billion light-years away from us, the distance light could have traveled in the 14 billion years since the big bang. But because the universe is expanding, the space traversed by a photon expands behind it during the voyage. Consequently, the current distance to the most distant object we can see is about three times farther, or 46 billion light-years.
Well, if I'm reading your use of quotes in your post correctly, you quoted the first part of that statement, and paraphrased the second part.Naty1 said:I reread the article by Lineweaver and Davis and sure enough they got it right here:
Somehow I got an excerpted quote wrong, but it was copied not rewritten (not retyped) , so I'm stumped...anyway, I updated my notes with the correct excerpt.