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Author Topic:   How big is our Galaxy.
Iblis
Member (Idle past 3895 days)
Posts: 663
Joined: 11-17-2005


Message 106 of 147 (279956)
01-18-2006 11:45 PM
Reply to: Message 104 by Percy
01-18-2006 9:54 PM


Re: Relativistic vs Doppler
Thanks, I get it now!
It does sound like we agree, but I thought Cavediver said this was wrong, and earlier I thought you agreed with him
We agree in our method for imagining or modeling the universe, but this model is technically false. It's still a good model, at least as good as the stretched rubber-band model which is very widely used to help us visualize the effect. The thing our rubber-band would need next to more closely correspond to the reality would be a telegraph line from one end to the other that slowed down the "apparent" speed of the messages so we observed them as being very slow at great distances. But the model would still be inadequate, one of the reasons it would be inadequate is because it can be say only 6 feet long and we can watch both ends at the same time.
I went ahead and read your galaxy-across-the-room bit over again and tried to take it very seriously this time, and I'm ready to poke at it a little now I think
a galaxy retreating from us at .99c, comparing the case where it is most of the way across the visible universe versus just across the room
But, there aren't any galaxies across the room from us who retreat that fast! I'm not being flippant, I'm saying that local bodies traveling at such great speeds in relation to us are very very rare. The most common thing along these lines would be some quantum physics particles that we can manage to observe for only brief moments. Now if there were such a body, say a great big rock that happened to wander through near-earth orbit at this kind of velocity, our observation of it would be just as you describe. In fact, depending on when we noticed it, by which I mean once it was in fact retreating, we might end up thinking it was much further away than it actually was. But, as we observed it again and again over time our error would become apparent I think.
What we see in terms of expansion behaves differently than this. We can look at objects close enough to estimate a distance for them using parallax and whatnot heading up your Cosmic Distance Ladder. And as we do this we can observe that objects at a great enough estimated distance have more red-shift than we would expect, as if they were moving away from us. Furthermore, other objects at about the same estimated distance have the same degree of red-shift! In any direction! Furthermore, the very farthest distances we can observe (on our radio) have essentially infinite red-shift. That last bit of signal has been perpetuated eternally at us and so on as I ranted about enough already, it's a signal artifact.
Now from a ballistical viewpoint that means the farther stuff is away from us the faster it is moving in the opposite direction. Consistently! It would be a very remarkable coincidence if we were really the center of the universe wouldn't it? Whereas Einstein's General Relativity, which explains a lot of other things like the fact that gravity isn't instantaneous but instead propagates toward us at or below c like any other phenomenon, also allows for space to be expanding in some uniform manner that would describe the consistency we see in red-shift at distances.
Here's how it works. First imagine space as a grid of points. Start by imagining it as a grid of equidistant points, like the vertices of the lines on graph paper. This is the geometry of Special Relativity, it accounts for gravity by basically allowing it to be magic. That is, bodies exert an unexplainable attractive force based on proximity, space itself is flat. Perfectly good for what at that point were greater distances than anyone except science-fiction authors had ever imagined us going anyway, basically a curiousity, a snotty modern-math attempt to improve on Galileo.
But, it produced some theoretically observable paradoxes, it didn't cover all the facts, it relied on Newton to be right while also implying he was wrong, it needed improvement. This led to General Relativity, which has the same principles of motion as Special Relativity but accounts for gravity in another way than simple "black magic". The way it does this is by dropping the "equidistant" rule for the points, allowing space to be "curved".
Mass in this model is not just something that has to be accelerated using force like the ballistic model of Special Relativity, it is also a contracting of space, a progressive movement-closer-together of the points on our grid. Objects moving through the grid near more massive objects find themselves closer to the object than they would otherwise expect not because of some "attractive force" but because the deck is stacked against them moving away and for them moving toward.
The reason that acceleration is the same as gravity is because moving through space at an increasing speed, normal space without much gravity, relatively equidistant points as it were, is the same phenomenon as simply existing or moving at what should be a steady speed where the space itself is contracted. Both phenomena, geometrically, consist of hitting the points faster and faster. From a practical viewpoint, trying to make a distinction between the two is implying that we don't fall at a geometric rate but rather at a steady rate, we know this is false. Or implying that what gravity does to us isn't faster and faster motion in the same way that acceleration is.
With me so far? Now, as it turns out, just as Mass is (among other things) a contraction of space, so in the same way Universe is (among other things) an expansion of space. Just as gravity causes us to hit the earth much faster than we might think we would if we had launched ourselves towards it at 5 feet per second and expected inertia to keep us going at that speed, so also expansion causes us to get to Andromeda (or better yet some distant quasar) much more slowly than we would expect to.
Here now, this is the gold. I'm going to resort back to our old models, we have two guys coming right up on the opposite ends of some rubber-band being stretched. Let's say it's 500 miles long at this point. They are walking along at 5 miles an hour. The stretching is such though that their "apparent" speed in relation to one another is say 100 miles an hour at this point. They have a 500 mile long rope with a noose on either end, around their necks. Their heads shoot off at what speed?
If their relative motion isn't real, it's only ten miles an hour. But their relative motion is real, their heads shoot off at 110 miles per hour. No doubt about it. So, if their relative motion is real, the time-dilation we observe is also real, relative to us. The reason the paradox it produces (each clock moving much more slowly than the other) isn't a problem is because it isn't really observable, only calculable. (We can't observe from both ends at the same time, the observer at either end never actually sees a paradox, only the math sees it.)
* credit to Lorentz, Hubble, Hawking and everyone else whose name should have come up in this already-way-too-long explanation
* and edited to correct blatant brain-farts
This message has been edited by Iblis, 01-19-2006 12:39 AM

This message is a reply to:
 Message 104 by Percy, posted 01-18-2006 9:54 PM Percy has replied

Replies to this message:
 Message 107 by Percy, posted 01-19-2006 4:18 PM Iblis has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 107 of 147 (280053)
01-19-2006 4:18 PM
Reply to: Message 106 by Iblis
01-18-2006 11:45 PM


Re: Relativistic vs Doppler
Iblis writes:
We agree in our method for imagining or modeling the universe, but this model is technically false. It's still a good model, at least as good as the stretched rubber-band model which is very widely used to help us visualize the effect. The thing our rubber-band would need next to more closely correspond to the reality would be a telegraph line from one end to the other that slowed down the "apparent" speed of the messages so we observed them as being very slow at great distances. But the model would still be inadequate, one of the reasons it would be inadequate is because it can be say only 6 feet long and we can watch both ends at the same time.
I've never thought of the rubber band model as a real rubber band, but as an infinitely stretchable rubber band. And it's not really a model, just an analogy to make clear the distinction between motion *through* space versus expansion *of* space. It isn't intended as an analogy to or model of relativity.
But, there aren't any galaxies across the room from us who retreat that fast! I'm not being flippant, I'm saying that local bodies traveling at such great speeds in relation to us are very very rare.
But this is only a thought experiment. If it helps, replace galaxy with the object of your choice. The goal is to understand how relativity works, and considering only real world situations is limiting. Einstein imagined himself traveling on a light beam. Why would you object to considering an object across the room traveling at near light speed so as to remove the expansion of space as a significant consideration?
Remember those math problems in grade school that went like this: "A locomotive leaves the station and travels 30 mph for 20 minutes and 50 mph for 30 minutes. How far has it traveled?" If you were like me you raised your hand and said, "But teacher, the locomotive couldn't instantaneously accelerate to 30 mph, and later instantaneously accelerate to 50 mph." True, but beside the point. It's the grade school equivalent of a thought experiment. Ignore the acceleration, just do the problem, the teacher would say, shaking her head. Jason in Foxtrot comes to mind.
Furthermore, the very farthest distances we can observe (on our radio) have essentially infinite red-shift. That last bit of signal has been perpetuated eternally at us and so on as I ranted about enough already, it's a signal artifact.
The furthest objects cannot have infinite red shift because Doppler effects can increase wavelength by only a factor of 2 in the limit as retreating velocity approaches c. It is the tinyness of Doppler effects as compared to relativistic effects that leads me to usually not make explicit reference to them in these discussions. I'm not trying to ignore them, but they're horribly mundane compared to the complexity of SR, GR and the expansion of space. There are no weird twin paradoxes posed by Doppler effects. No clock is actually affected by Doppler effects, only the time of our observation of those clocks because of the increasing distance light must travel.
Now from a ballistical viewpoint that means the farther stuff is away from us the faster it is moving in the opposite direction. Consistently! It would be a very remarkable coincidence if we were really the center of the universe wouldn't it?...etc...
I appreciate the effort, but you've gone way too basic on me. I apologize for leaving the impression I'm ignorant of all this, but it's an excellent presentation and I'm sure many lurkers will find it useful.
Here now, this is the gold. I'm going to resort back to our old models, we have two guys coming right up on the opposite ends of some rubber-band being stretched. Let's say it's 500 miles long at this point. They are walking along at 5 miles an hour. The stretching is such though that their "apparent" speed in relation to one another is say 100 miles an hour at this point. They have a 500 mile long rope with a noose on either end, around their necks. Their heads shoot off at what speed?
If it were a model it might be fair to pose these kinds of questions, but it's only an analogy.
I'm not sure of your position on my retreating object example. Do you accept the time of 8.08 seconds that I calculated for the time we observe it takes the object's clock to tick one second when the object is retreating at .99c with our observations beginning when the object is across the room?
--Percy
This message has been edited by Percy, 01-19-2006 04:19 PM
This message has been edited by Percy, 01-19-2006 04:21 PM

This message is a reply to:
 Message 106 by Iblis, posted 01-18-2006 11:45 PM Iblis has replied

Replies to this message:
 Message 108 by cavediver, posted 01-19-2006 7:15 PM Percy has replied
 Message 109 by Iblis, posted 01-19-2006 7:25 PM Percy has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 108 of 147 (280085)
01-19-2006 7:15 PM
Reply to: Message 107 by Percy
01-19-2006 4:18 PM


Re: Relativistic vs Doppler
Percy and Iblis, sorry for not being able to partake in this for these last few days... my workload has been cosnsiderable. I will try and pick this up again over the weekend, but just for now I will make a comment based on Percy:
The furthest objects cannot have infinite red shift because Doppler effects can increase wavelength by only a factor of 2 in the limit as retreating velocity approaches c. It is the tinyness of Doppler effects as compared to relativistic effects that leads me to usually not make explicit reference to them in these discussions. I'm not trying to ignore them, but they're horribly mundane compared to the complexity of SR, GR and the expansion of space. There are no weird twin paradoxes posed by Doppler effects. No clock is actually affected by Doppler effects, only the time of our observation of those clocks because of the increasing distance light must travel.
No, no, no. The cosmological doppler IS relativistic. It cannot be otherwise. Please do not use "relativistic" to mean SR effects, especially as there are no SR effects in cosmology, only approximations to SR effects which come from the GR metric... precisely where the cosmological redshift and gravitational redshift originate.
The cosmological redshift is not conventional classical doppler. There is no "retreating velocity". You cannot equate the expanding space to a simple effective velocity of recession. The doppler effect of expanding space is anything but mundane! The redshift parameter is unbounded, not bound by 2... which is a good job for all those thousands of z>2 objects we have discovered! The farthest quasars are z>6. Iblis is quite correct in this.
Oh, and while i remember: acceleration is prefectly fine in SR. You do not need GR. You only need GR where curvature is involved.
This message has been edited by cavediver, 01-19-2006 07:25 PM

This message is a reply to:
 Message 107 by Percy, posted 01-19-2006 4:18 PM Percy has replied

Replies to this message:
 Message 110 by Percy, posted 01-19-2006 8:16 PM cavediver has replied
 Message 117 by Percy, posted 01-20-2006 10:30 AM cavediver has replied

  
Iblis
Member (Idle past 3895 days)
Posts: 663
Joined: 11-17-2005


Message 109 of 147 (280088)
01-19-2006 7:25 PM
Reply to: Message 107 by Percy
01-19-2006 4:18 PM


Relativistic = Doppler (plus Brad McFall)
way too basic on me. I apologize for leaving the impression I'm ignorant of all this
No no please I am the one who may be ignorant of these most basic ideas, in collecting my thoughts I found it necessary to talk through the whole thing completely and show my work so that people smarter than me can correct if needed and so that I can refer back to it later for the real statements I am trying to make. The only part of the post specifically pointed at you (as something you need to understand and don't seem to) is the rubber-band / tandem-gallows bit at the end, indicated as such with the introductory "Here now, this is the gold ... "
I was so brain-burned at the end of my little exposition that I was only able to get to this one part of the idea thereafter, and even so and even with rigorous editing I still screwed it up. For example the "they" in "their relative speeds" should be the ends of the rubber-band, not the guys, or else the head-popping-off speed should be that speed 100 mph.
Also, we will need a magic rope It has to be infinitely strong, massless, dragless, cut through necks like water but remain attached to heads somehow, and any number of other unrealistic properties. You get this though already I know, you recognize that the rubber-band has magic properties, my rope just needs totally different magic properties. The train moving at 30 mph and then suddenly 50 mph, these kind of unreal properties aren't a problem with your thought-experimenting, that's fine.
Here's the problem though, whatever analogy we use to make you see it, the motion is still real, the sudden stop is still real. Let's say an orbiting satellite shoots down a weight on the end of a long cable at 5 mph and lets it fall freely until it gets to the end of the cable. Will the stress of the stop and its effect on the satellite, weight and cable be consistent with 5 mph, or will it be consistent with say 5 mph plus 32 feet per second squared times the length of time needed to get to the end of the cable? If the "apparent" speed / acceleration produced by gravity is real, then the speed / acceleration produced by expansion is equally real. Why wouldn't it be?
There are no weird twin paradoxes posed by Doppler effects. No clock is actually affected by Doppler effects
Here is where we seriously seriously disagree, and where I am the one trying to agree with GR. The time-dilation created by what we are splitting off as merely "doppler effects" is just as real, relative to the observer, as the time-dilation created by what we are accepting as genuine "relativistic effects". The "space as a series of non-equidistant points" routine is supposed to make sure this is clear, obviously it hasn't.
The reason we would like to believe that the time-dilation described as doppler effect is somehow less real than the time-dilation caused by other relative-speed effects is that it cancels out when we turn around and come back. But this is wrong, gravitational effects also cancel out when we turn around and come back (all the energy magically gained by falling must be "put back" when rising.) Yet the motion, speed, and potential impact force involved in gravitation are definitely real aren't they?
Once you recognize that there's no such "real" difference in what you are calling doppler and what you are calling relativistic in terms of the (relative) time-dilation they produce, something interesting becomes apparent about our grid of points. Objects travelling away from us undergo slightly more time-dilation than objects traveling past us and even more than that compared to objects travelling toward us. At very great distances, which in our expanding universe also means very great speeds, this part of the time-dilation is the vast majority of the effect.
An object travelling through space is a contraction of space ahead of the object and an expansion of space behind it. The one doesn't "cause" the other either, as if it were motion that were warping space; they are two different methods of describing the same geometrical function. The space is only warped relative to the object and observer though, the part we are calling "doppler effect" is due to the observed light coming from the moving object and the part we are calling "relativistic effect" is due to the final measurement after the two-way trip has been made and the doppler dilation / compression has canceled itself out, leaving only the Lorentzian transformation math to be accounted for.
A distant object being "expanded" away from us has that same expansion of points behind it, therefore again the relativistic effect is the same as normal motion. The place where it differs is on the other side of the object from us, which is also expanding rather than contracting as it would if the motion were what you are thinking of as "real motion" through space. The local effect there is thus different, but not the relative effect here.
Do you accept the time of 8.08 seconds that I calculated for the time we observe it takes the object's clock to tick one second when the object is retreating at .99c with our observations beginning when the object is across the room?
Here's my real problem, I know I don't really understand Lorentz and Poincare. I would prefer for the time-dilation to make sense to me, i e if I am trveling at 150,000 kps (.5c) and yet light still seems to be traveling at c (300,000 kps) then in order for me to observe it that way my time should be slowed down to only .5 of its original rate. If I am travelling at .75c and yet light still is going c (relative to me) then my experience of time should only be .25 of what it was. Do you see my logic?
But I am wrong, wrong, wrong; and I do not know how to imagine it in such a way that I make the correct deductions. All I can do is look at the table and say Well what you are saying seems to match what I am reading on the table. I will be happy to agree with your math though if I can count on you not to intentionally deceive me, if that helps.
If it helps, replace galaxy with the object of your choice
Yes I did that, I shot a big rock through near-earth orbit and conceded if we did see such a thing the effect would be just as you described. Assuming that we could still see the same rock across the universe where everything is traveling an "extra" .99c away from us, the fact that it was also still traveling .99c relative to all that local stuff would not, so far as I can tell, have a very large effect on our observations. Maybe you can improve my understanding of this?
My math may be afu again, would the total speed relative to us be something like .9999c at this point? How large a difference does that make (from .99c) in the Lorentz transformation? If it's a great difference then I guess it would be observable even at that great distance. From a practical point of view though, the vast majority of local objects are moving at less than .1c relative to each other, and that little margin definitely won't make any difference moved across the universe when added to the .99c relative to us caused by the expansion. And much less using Lorentz's real math than the simple symmetry that I would like for it to be, in the real world .1c has almost no effect in terms of time-dilation instead of the .9 I would like to imagine it as.
Is any of this helping? I noticed that you spoke of relativistic effects as if they were actually doing something to the local clocks, they aren't really though. The local clock continues to tell time second by second in a way that looks fine locally. No one in the spaceship feels any time-distortion, a one-minute egg still takes 60 ticks to cook. It isn't affecting the home observer's clock either, how could it? There's no magic action-at-a-distance. What the relative motion is doing is distorting the spacetime between the two clocks. And that's the same thing that expansion is doing, the same thing that gravity is doing, the same thing that acceleration is doing. In every case some points are (relatively) closer together and some points correspondingly farther apart.
Brad McFall writes:
that expansion and acceleration(or gravity) were two different things. This thought caused some confusion for me when thinking about entropy
Thanks Mr. McFall, I hadn't thought of it but entropy (propagation of energy) opens up another source of examples of why General Relativity is the best approximation of what mass/energy and space/time are really doing. I will ponder for a bit and see if I can mine some of these for helpful thoughts.
To start with we must go ahead and distinguish between normal acceleration, caused by the necessarily uneven application of force and resulting in relative compression / dilation of spacetime, and gravitation caused by compression / dilation and resulting in the relatively even attainment of force or acceleration.
What this has to do with entropy, which is probably so simple it isn't one of the things you were thinking of at all, is that if gravity were a force it would act unevenly, resulting in a "feeling" of acceleration like that we get when firing a rocket or riding in Einstein's elevator (rather than fee-fall that is). This force would eventually have to run out, entropize into nothing, whereas we can expect gravitation to continue as long as the mass continues to exist and distort the space in the same way.
Someone has just pointed out to me though that the continued expansion of space will necessarily decrease the space-distorting effect of mass over time, just not at anything like the rate that normal entropy would disperse a real force. So I guess I'm back to the drawing board until I have clearer ideas. In the meantime I'm reading your Goethe vs Newton link, this stuff is fascinating. Thanks again!
(Oh, if you get the chance, I would be honored to hear your thoughts on my previous post "When Worlds Collapse" Message 98 )

This message is a reply to:
 Message 107 by Percy, posted 01-19-2006 4:18 PM Percy has not replied

Replies to this message:
 Message 114 by Brad McFall, posted 01-20-2006 7:38 AM Iblis has not replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 110 of 147 (280093)
01-19-2006 8:16 PM
Reply to: Message 108 by cavediver
01-19-2006 7:15 PM


Re: Relativistic vs Doppler
cavediver writes:
No, no, no. The cosmological doppler IS relativistic. It cannot be otherwise. Please do not use "relativistic" to mean SR effects, especially as there are no SR effects in cosmology, only approximations to SR effects which come from the GR metric... precisely where the cosmological redshift and gravitational redshift originate.
Don't use relativistic to mean SR effects? So even though SR is short for Special Relativity, you're saying its effects shouldn't be described as relativistic. I know you qualified that to the cosmological context, but still.
I appreciate that it's difficult to find sufficient time to explain complex and easily misunderstood topics, and I appreciate that you're making the effort, but you haven't given me much to go on. I suppose I could memorize what you're saying so I could parrot it back, but my goal is understanding, not mimicry. Perhaps you could point me to a readily available layperson's book that has a chapter describing what you're trying to explain to me.
--Percy

This message is a reply to:
 Message 108 by cavediver, posted 01-19-2006 7:15 PM cavediver has replied

Replies to this message:
 Message 111 by cavediver, posted 01-20-2006 3:57 AM Percy has not replied
 Message 146 by cavediver, posted 06-30-2007 10:14 AM Percy has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 111 of 147 (280182)
01-20-2006 3:57 AM
Reply to: Message 110 by Percy
01-19-2006 8:16 PM


Re: Relativistic vs Doppler
Don't use relativistic to mean SR effects?
Sorry, I should have said "don't use relativistic to mean solely SR effects, to the exclusion of GR". You were splitting the red-shift effect into doppler and relativistic, which undermines the very important fact that the doppler is a very relativistic effect.
To produce the red-shift calculations you have to go to the metric. In fact, just about every calculation in GR revolves around the metric. Do you want me to go through some of the maths with you? It's not that hard, though typesetting is a pain... any suggestions for inserting equations on this forum?
I don't know of any layman book which will increase your knowledge. I'm afraid it's text book time. Essential Relativity by Rindler is probably my choice for your particular line of questioning. He is less mathematical and heavily into cosmological models.
This message has been edited by cavediver, 01-20-2006 04:00 AM

This message is a reply to:
 Message 110 by Percy, posted 01-19-2006 8:16 PM Percy has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 112 of 147 (280187)
01-20-2006 4:17 AM
Reply to: Message 101 by Iblis
01-17-2006 11:03 PM


Re: Relativistic vs Doppler
It's still nonsense though. I can accept it, I can do math with it, but I can't ever "understand" it. The only thing that makes it even remotely tolerable is that we can't ever meet. If we could somehow "suddenly" meet under these circumstances, we could compare clocks, and one would either be slower than the other or else they would agree.
The one who had journied would always measure less time from the big bang than the one who had not. It cannot be otherwise. Geodesics are (perversely) the LONGEST path between two points in space-time. Any deviation (acceleration) from a geodesic will shorten the path and hence less time will have elapsed. It is purely the acceleration that is responsible for the twin's paradox in SR.

This message is a reply to:
 Message 101 by Iblis, posted 01-17-2006 11:03 PM Iblis has replied

Replies to this message:
 Message 113 by Iblis, posted 01-20-2006 7:18 AM cavediver has replied

  
Iblis
Member (Idle past 3895 days)
Posts: 663
Joined: 11-17-2005


Message 113 of 147 (280199)
01-20-2006 7:18 AM
Reply to: Message 112 by cavediver
01-20-2006 4:17 AM


Re: Relativistic vs Doppler
I'm, not sure how to read this. I get the twins paradox, it isn't really a paradox it's just a weird effect. The twin who travels ages much more slowly than the one who stays at home, eventually returns to earth and marries his own great-great-great-granddaughter. No problem. Near-light travel slows relative aging, all good. Not what I'm complaining about, no no. Here's what I'm complaining about
Zigfax lives say 5 billion light years north of us, Bemfu lives say 5 billon light years south of us. They don't travel at all, relative to their own planets, they stay right where they are. They are of near-immortal races, aware of one another somehow, and beam clock-images back and forth as well as analyses of their respective clock-images and conclusions about them. We are in the middle and eavesdrop on their conversation.
From Zigfax's point of view, Bemfu ages much more slowly because he is the one travelling away at near-light speeds (thanks to expansion). From Bemfu's point of view Zigfax is the one travelling at near-light speeds and therefore aging much more slowly. We in the middle observe them both as aging a bit more slowly than us, at least as of 5 billion years ago when the latest message was sent from either. We also observe their conclusions about each other, which provide the paradox.
Our "doppler vs relativistic" distinction allows us to rest comfortably knowing their math isn't real. It's just "doppler effect" and really they age at the same speed. GR says no, there's no difference, they really do age each slower than the other. Another couple billion light years in each direction, they age not at all relative to one another, or even (as calculated but never observed) in reverse from one another. Yet each one continues aging normally on his own planet where he is.
That's a real paradox, just not an observable one.

This message is a reply to:
 Message 112 by cavediver, posted 01-20-2006 4:17 AM cavediver has replied

Replies to this message:
 Message 115 by cavediver, posted 01-20-2006 7:43 AM Iblis has replied

  
Brad McFall
Member (Idle past 5032 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 114 of 147 (280203)
01-20-2006 7:38 AM
Reply to: Message 109 by Iblis
01-19-2006 7:25 PM


Re: Relativistic = Doppler (plus Brad McFall)
I will come back and comment more coherently, relating to your post, to read it and the thread as a whole etc., but I can comment right now on:
quote:
What this has to do with entropy, which is probably so simple it isn't one of the things you were thinking of at all, is that if gravity were a force it would act unevenly, resulting in a "feeling" of acceleration like that we get when firing a rocket or riding in Einstein's elevator (rather than fee-fall that is). This force would eventually have to run out, entropize into nothing, whereas we can expect gravitation to continue as long as the mass continues to exist and distort the space in the same way.
because before reading about the problems with Prigogine's ideas that Georgi Gladyshev (http://EvC Forum: GP Gladyshev's paper (s)or mine? -->EvC Forum: GP Gladyshev's paper (s)or mine?) solidified in my thinking
quote:
At that time, the most fashionable theory was probably the one formulated by Ilya R. Prigogine and his colleagues. It maintained that open natural biological systems are far from equilibrium. This seemed to imply that they (such systems) can be formed and exist only as a result of the formation of ?live? dissipative structures. I would like to note that under dramatic changes of the environment?s parameters (I call such changes revolutionary, as opposed to evolutionary), individual biological systems function in conditions that are far from equilibriums. In such conditions one can, indeed, observe the emergence of dissipative (dynamic) structures. However, the role of these structures in the evolutionary development of living objects is not determinative. In my view, Prigogine?s theory was a dead end in terms of thermodynamics or, at best, in Roger Penrose?s terms, a trial one. Still, many researchers remain faithful to these views, although, as applied to evolutionary biological processes, there is not a single even semi-quantitative argument in favor of Prigogine?s theory. Also, delusions in the area of thermodynamics of biological evolution are promoted, as before, by the serious errors arising from a mistaken idea of entropy and interpretation of the second law. Because of these errors, inflated by visionaries-cum-dilettantes, many biophysicists neglect the works of Gibbs and the other classics. The fathers of ?postnonclassical? science (which, in my view, is hardly related to science at all) have most probably made no serious study of physical chemistry and other fundamental works. Following in the steps of Kenneth Denbigh, I have recently devoted several publications to these matters.

, I HAD considered the possibility, I think, you referenced.
Imagine, gravity clinematic differences ( g-force can interact
http://EvC Forum: Information -->EvC Forum: Information
http://EvC Forum: Evolution vs.PE -->EvC Forum: Evolution vs.PE
http://EvC Forum: Evolution vs.PE -->EvC Forum: Evolution vs.PE
Collections Search | Smithsonian Institution Archives
Just a moment...
Nace had found that there were energy indications to suspect gravity played a part in space flight changes in physiology.
with torque on cell contents differentially if the size is larger than bacteria) in a dissipative system. If gravity is dissipatively active over(beyond) themal effects then the "elevator effect" could interact physiologically with actual physical chemical movements that DO contribute to entropy!! This is the kind of thing I mention if I must compare my own ideas of what is going on inside a cell with Behe's Jonny-come-later approach seems to garner preferntially to my comments. My thinking has a become less ugly than this however.
Thanks for responding. I dont have more time this morning, more later.
This message has been edited by Brad McFall, 01-20-2006 12:43 PM

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 115 of 147 (280204)
01-20-2006 7:43 AM
Reply to: Message 113 by Iblis
01-20-2006 7:18 AM


Re: Relativistic vs Doppler
It's just "doppler effect" and really they age at the same speed. GR says no, there's no difference, they really do age each slower than the other.
No, they perceive each other as aging more slowly. They are actually aging at exactly the same rate, as they are at rest in comoving frames. If you were in one galaxy and travelled to the other, which you had perceived as aging more slowly, by the time you go there it would be YOU that was young, not them! (as a result of your acceleration).
This is almost identical to SR. Two observers at some relative velocity will perceive each other as aging more slowly. Both are just perceptions. There can be no true stationary observer in SR (unlike GR, where a stationary observer is one who is stationary wrt the comoving frame) Only when you accelerate sufficiently to make yourself stationary wrt the other observer do you realise that it is YOU that are the one that has aged slowly (as a result of your acceleration).
This message has been edited by cavediver, 01-20-2006 07:47 AM

This message is a reply to:
 Message 113 by Iblis, posted 01-20-2006 7:18 AM Iblis has replied

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tsig
Member (Idle past 2908 days)
Posts: 738
From: USA
Joined: 04-09-2004


Message 116 of 147 (280209)
01-20-2006 8:04 AM
Reply to: Message 102 by Percy
01-18-2006 2:42 PM


mystey
post deleted
tried twice
failed thrice
This message has been edited by ts, 01-20-2006 08:17 AM

This message is a reply to:
 Message 102 by Percy, posted 01-18-2006 2:42 PM Percy has not replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 117 of 147 (280242)
01-20-2006 10:30 AM
Reply to: Message 108 by cavediver
01-19-2006 7:15 PM


Re: Relativistic vs Doppler
Hi Cavediver,
I went back to this message after reading your clarification about use of the word "relativistic" and I think I understand this part now:
The cosmological redshift is not conventional classical doppler. There is no "retreating velocity". You cannot equate the expanding space to a simple effective velocity of recession. The doppler effect of expanding space is anything but mundane! The redshift parameter is unbounded, not bound by 2... which is a good job for all those thousands of z>2 objects we have discovered! The farthest quasars are z>6. Iblis is quite correct in this.
I already knew about z, but I had never tried to look at it as evidence for the expansion of space. If you take the Hubble constant as 71 km/s/Mpc and you multiply it by the distance to the edge of the observable universe, about 4200 Mpc, you get the speed of light. This says that the furthest reaches of the observable universe, those that are very close to the big bang, are receding from us at nearly the speed of light.
But how do we know it is this distant space (and the objects it contains) that is receding, and that it's not just a case of the objects themselves receding through a space which is not expanding? There apparently is this Ives/Stilwell experiment that verifies this is the proper way of viewing things, but I found the math too challenging to figure out why.
But while looking into this I did discover that there is a different version of the Doppler effect equation that is used for electromagnetic radiation, and it includes the Lorentz transformation. In other words, it was invalid for me to apply sound-style Doppler to light. And the relativistic Doppler equation appears to take into account both relativity effects and longitudinal motion effects. I can see that for transverse motion the equation reduces to the Lorentz factor. So both longitudinal and transverse components of motion are accounted for in a single equation. See Relativistic Doppler effect - Wikipedia for the equation I'm looking at. It's the first one.
I recall complaining at one point in my earlier discussion with Sylas that what science writers for the layperson level consider sufficiently detailed seems to have increased in the 20 years since I last looked at relativity. Ways of saying things that no one would have batted an eyelash at 20 years ago are now considered either wrong or inaccurate or misleading, and I've been making bad interpolations while trying to fill in the blanks.
A fundamental question that I should have been asking 20 years ago: Why did Einstein (and before him Lorentz) "know" the Lorentz transformation was required for electromagnetic radiation?
Iblis, thanks for your posts, I'll catch up with them when I can. Ultimately I'd like to understand how we know space is expanding and how to properly interpret observations made within an expanding space, but I think I'm further from the goal than I originally thought.
--Percy

This message is a reply to:
 Message 108 by cavediver, posted 01-19-2006 7:15 PM cavediver has replied

Replies to this message:
 Message 118 by cavediver, posted 01-20-2006 11:10 AM Percy has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 118 of 147 (280268)
01-20-2006 11:10 AM
Reply to: Message 117 by Percy
01-20-2006 10:30 AM


Re: Relativistic vs Doppler
Percy, got to be quick. Check out this link and the following pages. After a quick glance I think they are very good. Especially check out the diagrams on pages 3 and 4.
Why did Einstein (and before him Lorentz) "know" the Lorentz transformation was required for electromagnetic radiation?
Lorentz postulated the transformations as a way of explaining the null MM experimental results. Einstein noticed that Maxwell's wave equations were Lorentz invariant... which leads to the constancy of c.

This message is a reply to:
 Message 117 by Percy, posted 01-20-2006 10:30 AM Percy has replied

Replies to this message:
 Message 120 by Percy, posted 01-20-2006 12:20 PM cavediver has replied

  
Brad McFall
Member (Idle past 5032 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 119 of 147 (280283)
01-20-2006 12:08 PM
Reply to: Message 98 by Iblis
01-16-2006 7:36 PM


Re: When Worlds Collapse
I am much more a biologist than a physicist although both of my brothers proclaim to know something of the latter more than me, but sometimes I wonder...
Thus I am more in tune with the Erhlich/Simon disagreement about the amount of copper than how Hawking flip-opped on what information can or can not come out of a black hole.
If the size of our galaxy depends on how far in the infinite time-future human beings explore beyond a determinate point, a point say named by Newton, then my ideas about how gravity *might* be causally equilibrated in organisms may bear in the hearing on this thread's subject, however one would clearly need to distinguish chemistry of non-linear physics from the analytic at equilibrium population genetics and I am not prepared for that discussion which shows that recent criticism of Wright is not justified as to the future of agriculture and the dominion mandate because of lack of understanding/appreciation of the intricacy involved.
It was an evc-thing to witness Percy and Sylas discuss the expansion of space. I am sure Percy can bring the conversation back through that diagram that Syals presented if you and Cavediver do not abate in conversation. I suspect that I missed some of the conversation about the aether through creationism but I will try to read the rest of this thread to see if I can address some creationistic interpretations of Einstein OR Lorenz. I for one find imagining my self next to a lightwave non-intuitive but I have little problem with suspecting the law of straight line motion of Newton within the space that expands during biological evolution does not occur. I often think it does. If however this is related to my former conflation of entropy with universal expansion (as to the energy of ?what mass??)I can do no good but distract from the well posted messages say between Percy and CaveDiver as well as you here interalia.
On a personal note, friends often remarked about the youngest boy in our family who picked up on the black hole that my other brother and I were discussing, as he would often bring the subject up repeatedly, yet he was only about 8 then.
This message has been edited by Brad McFall, 01-20-2006 12:12 PM
This message has been edited by Brad McFall, 01-20-2006 12:13 PM

This message is a reply to:
 Message 98 by Iblis, posted 01-16-2006 7:36 PM Iblis has replied

Replies to this message:
 Message 124 by Iblis, posted 01-21-2006 10:28 AM Brad McFall has replied

  
Percy
Member
Posts: 22391
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 120 of 147 (280289)
01-20-2006 12:20 PM
Reply to: Message 118 by cavediver
01-20-2006 11:10 AM


Re: Relativistic vs Doppler
cavediver writes:
Percy, got to be quick. Check out this link and the following pages. After a quick glance I think they are very good. Especially check out the diagrams on pages 3 and 4.
These pages were also referenced in the previous discussion with Sylas. Working my way through, I have a question on page 1, http://www.astro.ucla.edu/~wright/cosmo_01.htm:
1 + z = sqrt((1+v/c)/(1-v/c))      so     v = cz + ...
but the higher order corrections (the "...") in cosmology depend on general relativity and the specific model of the Universe.
v=cz means that for values of z greater than 1, v is greater than c. So two things. I don't see how he concludes v=cz from the simplified relativistic Doppler effect equation. Does his "..." somehow account for that? If so, how? And anyway, such a conclusion seems to contradict the equation, since you can rework the equation to solve for v/c, and if, for example, you plug in z=6, you get v/c=49/51. For increasing values of z, v/c only gets closer and closer to 1. It never exceeds 1. v never exceeds c.
--Percy

This message is a reply to:
 Message 118 by cavediver, posted 01-20-2006 11:10 AM cavediver has replied

Replies to this message:
 Message 121 by cavediver, posted 01-20-2006 12:55 PM Percy has replied

  
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