Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: bizerl on 05/10/2012 05:32:44
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in a previous post (http://www.thenakedscientists.com/forum/index.php?topic=45631.0), it was mentioned that:
Anything in space hitting you when you are doing .97c will punch a hole straight through your space ship - and the background radiation of the universe will be blue-shifted upto very uncomfortable temperatures.
This made me think, If we could accelerate fast enough, could we reach a point where the red-shifting of the CMBR was reversed and we would be able to extrapolate a visible picture of the early universe?
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To an extent we don't need to. The cosmological principle can be used to assume that all the CMBR we measure (ie in every direction) has been affected by exactly the same amount of red-shifting - so we can say that any anisotropies (blotches/irregularities) that we see now are the fossil evidence of primordial disturbances. So to an extent we are blue-shifting in a computer.
Additionally - the era of last scattering (when the CMBR was produced and released) was incredibly boring - the universe was an ALMOST homogeneous soup of plasma; the tiny differences have been kept and diluted so we have to look a vast scales now to predict the smallest anomaly then. You can search on Wilkinson Microwave Anisotropy Probe - which is looking for those very differences in the CMBR http://en.wikipedia.org/wiki/WMAP
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Before I tackle the real puzzle, let's clear up some minor errors. If "anything" refers to a grain of sand, for instance, it probably won't go straight thru your space ship; instead, it will explode at the surface like a small atomic bomb and vaporize a large part of the ship.
I disagree with the statement that, "...the background radiation of the universe will be blue-shifted up to very uncomfortable temperatures." Temperature is inversely proportional to wavelength. To heat the CMBR in front to 0°C, you would need a relativistic Doppler shift of 273 K / 2.7 K = 101.1, which corresponds to a relative speed of 299734 km/s = .9998 c. (To derive that, I went to Wolframalpha, input "relativistic Doppler shift", select "calculate speed of source away from observer" and "frequency reduction factor = 101.1". Since the reduction factor is greater than 1, the result is negative 299734 km/s. Click on that answer to convert to .9998 c.)
Now for the real brain buster! I'll have to solve the more general question of what the CMBR would look like to an observer moving at .97 c relative to practically all of the matter in the observable universe. I've been working on this, off and on, for a week.
Trying to solve this question has raised a number of other questions that puzzle me. Perhaps someone here can help. If you don't understand comoving coordinates (http://en.wikipedia.org/wiki/Comoving_distance), you won't understand my argument, so do some boning up, first. The increasing distance between distant galaxies is not considered to be a real velocity in comoving coordinates, so it does not contribute to the length contraction or time dilation of special relativity.
The key to solving this problem is in setting up two comoving coordinate systems, with relative motion between them at .9682 c in the +x direction, which corresponds to gamma = 4. They are comoving within themselves, but not comoving with each other.
One system, F0, is comoving relative to Earth. Since known galaxies have only minor proper motion (compared to .9682 c), we may consider that all galaxies in the visible universe are comoving with Earth. In other words, the only significant motion between us and the galaxies, in F0, is the expansion of space, and all galaxies are approximately motionless relative to their coordinates in this expanding coordinate system.
The other coordinate system is comoving relative to imaginary points in space, which are all moving at .9682 c relative to the corresponding points in F0. All galaxies are moving thru F1 at .9682 c, so an observer moving with F1 sees them length contracted to one fourth of their normal length in the x direction, and he sees their clocks running at one fourth normal speed.
Now, we must figure out how that time dilation affects the expansion of space in F1. We know that, in F0, space expands at the rate of H0 ≈ 2.5 x 10^-18/s in all directions. In F1, my first thought is that the galaxies are aging four times more slowly, so the space between galaxies must be expanding at .625 x 10^-18/s in all directions, according to F1 clocks.
This is where I run into doubts. Does this mean that F1 space expands at H0 /4? Is it the same in all directions? I need some help, here, guys.
Looking ahead, I plan to set my F0 clocks to zero at the instant when the primordial plasma first became transparent. I place my F0 origin at Earth. Then I plan to synchronize my F1 clocks so that clocks at x = x' = 0 show the same time as Earth clocks; i.e. 13.7 billion years. I want to know what the CMBR would look like to an observer at the origin of F1 as he passes Earth.
On second thought, maybe I should set my F1 clocks to zero at the instant when the plasma became transparent at the origin of F1; i.e. the point in F1 which is passing Earth, now. Note that the plasma did not become transparent everywhere at once in F1. That's because events at different x coordinates which are simultaneous in F0 cannot also be simultaneous in F1. That's just basic special relativity.
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I'm not sure how you defined this one Phractality. Are you assuming both systems F0 and F1 to be 'still' relative the expansion, in terms of co-moving, relative what? In F0 relative a planet inside the system, but in F1 relative some imaginary points in space, but made how? And how would they differ from using Earth as a coordinate? Either you assume that those points can be defined as unchanging even if considering a expansion, which I don't think is possible globally, as you from any other point must find fond those points positions to 'move' in a expansion?
If a expansion is related to the space around galaxies then you have only the points inside the galaxy to use, if on the other hand a expansion is allowed to exist inside the galaxies, gravity and mass (suns/planets) acting a buoys in the water, anchored relative each other keeping a same distance then no position can hold true? Except relative gravity/mass possibly. And then all positions become 'relative', relative a expanding vacuum.
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If I assume all galaxies as being 'unmoving' relative each other, as in uniformly moving galaxies keeping their distance relative each other (Ignoring a 'expansion' that should mean, not their motion relative each other:). Then arbitrarily defining any of them as my 'point of origin' will present me with different time dilations/length contractions, depending on how I define my relation relative that other galaxies 'relative motion'. And as each galaxy can be used as that point of origin, and as we can assume us to measure different 'speeds' relative those other galaxies it all becomes a relative question what length contraction, or time dilation, you might expect measuring. Or maybe I'm missing the point here?
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I'm not sure how you defined this one Phractality. Are you assuming both systems F0 and F1 to be 'still' relative the expansion, in terms of co-moving, relative what? In F0 relative a planet inside the system, but in F1 relative some imaginary points in space, but made how? And how would they differ from using Earth as a coordinate? Either you assume that those points can be defined as unchanging even if considering a expansion, which I don't think is possible globally, as you from any other point must find fond those points positions to 'move' in a expansion?
Good question. Best I can figure, you have to define the coordinate grid of F1 by its SR relation to the grid of F0. The grid of F0 is stationary relative to the comoving galaxies, and for the sake of argument, I'm assuming that all galaxies are comoving with Earth. You have to apply the SR formulas for both space and time to the F0 grid to define the space-time coordinates of the F1 grid. SR applies only to the relative motion between F0 and F1. In comoving coordinates, the expansion of space does not count as velocity for purposes of SR.
If a expansion is related to the space around galaxies then you have only the points inside the galaxy to use, if on the other hand a expansion is allowed to exist inside the galaxies, gravity and mass (suns/planets) acting a buoys in the water, anchored relative each other keeping a same distance then no position can hold true? Except relative gravity/mass possibly. And then all positions become 'relative', relative a expanding vacuum.
I'm only looking at the big picture; inside galaxies is the little picture. Relative to the comoving coordinates of F0, galaxies are shrinking internally, but at such a slow rate as to be inconsequential.
I think of comoving coordinates as idealized chain links of constant length. New links are being added continually to account for expansion of space. The centers of galaxies are stationary relative to the nearest chain links. The periphery of our galaxy are moving relative to their nearest chain links, toward the galactic center at about 1 km/s. For purposes of the present problem, that might as well be zero. We're only concerned about speeds close to the speed of light.
If I assume all galaxies as being 'unmoving' relative each other, as in uniformly moving galaxies keeping their distance relative each other (Ignoring a 'expansion' that should mean, not their motion relative each other:). Then arbitrarily defining any of them as my 'point of origin' will present me with different time dilations/length contractions, depending on how I define my relation relative that other galaxies 'relative motion'. And as each galaxy can be used as that point of origin, and as we can assume us to measure different 'speeds' relative those other galaxies it all becomes a relative question what length contraction, or time dilation, you might expect measuring. Or maybe I'm missing the point here?
The point you are missing, here, is the meaning of "comoving". That's not the same as "unmoving". I am ignoring all proper motion of galaxies, since it is inconsequential compared to .9682 c. I am not ignoring the increasing distance between galaxies due the expansion of space. I am assuming that all galaxies are comoving relative to each other, which means they have zero velocity relative to the comoving coordinates of F0. They are not length contracted or time dilated relative to each other in the comoving coordinate system, which is the system preferred by mainstream cosmologists. That's not to say that other coordinate systems are invalid; they just present a very different picture. If you are confused about which coordinate system you are using, you will be very confused, indeed.
The origin of F0 is arbitrary. I arbitrarily choose to place my origin at the point in F0 which is now occupied by Earth, or rather by the center of the Milky Way Galaxy.
The origin of F1 is slightly less arbitrary, since the primordial plasma did not become transparent at all points in F1 at the same time (by clocks synchronized in F1). I think the present problem is simplified by placing the origin of F1 at the point whose spatial coordinates are passing Earth now. The time origin of F1 is the time when the F1 clock which is now passing Earth was set to t = 0. Perhaps that clock should be set to zero at the instant when the plasma became transparent at the location of that clock in F1. So you have to apply the SR time formula to determine what time is showing on that clock as it passes Earth.
Since F1 clocks are running at 1/4 normal speed, as seen by F0 observers, I suppose that means the clock at the origin of F1 has counted off 13.7 billion years divided by 4, or 3.425 billion years, since it was set to zero. I am assuming that the relative speed between F0 and F1 has always been .9682 c. In other words, every grid point in F1 has always been moving past the nearest F0 grid point at .9682 c. Meanwhile, the distance between the spatial origins of F0 and F1 has been increasing at the rate of the Hubble parameter; i.e. doubling about every 9 billion years. I'm also assuming that the Hubble parameter has been constant since the plasma became transparent. In F0, the distance from Earth to the origin of F1 has nearly tripled in 13.7 billion years.
My brain hurts when I try to figure out the spatial distance between the origins of F0 and F1. Now we have to clarify what type of distance (http://en.wikipedia.org/wiki/Distance_measures_%28cosmology%29) we're talking about. I suppose the light-travel distance from Earth to the origin of F1 must be .9682 c times 13.7 billion years = 13.26 billion light years. Is the luminosity distance triple that much, since the distance has tripled due to expansion?
What's the formula to convert light-travel distance to luminosity distance.
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Yeah, I see what you mean, but to be concrete about a time dilation/contraction here you must need to consider what their motion is, relative each other, in any uniform motion, as I think? Consider A and B moving as one, 'at rest' with each other relative A and B meeting/passing each other. Maybe it's me needing to see how comoving is defined? I've thought of that as a 'mathematical device' simplifying the math by excluding the effect of an expansion, but? You still have galaxies moving in opposite directions and even if ignoring a expansion it should matter what velocity they have relative each other.
As for the rest i will need to read it carefully Phractality, and hopefully see how you think there tomorrow. It's quite late here now :)
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Yeah, I see what you mean, but to be concrete about a time dilation/contraction here you must need to consider what their motion is, relative each other, in any uniform motion, as I think? Consider A and B moving as one, 'at rest' with each other relative A and B meeting/passing each other. Maybe it's me needing to see how comoving is defined? I've thought of that as a 'mathematical device' simplifying the math by excluding the effect of an expansion, but? You still have galaxies moving in opposite directions and even if ignoring a expansion it should matter what velocity they have relative each other.
As for the rest i will need to read it carefully Phractality, and hopefully see how you think there tomorrow. It's quite late here now :)
While there are galaxies colliding or passing one another, those relative speeds are generally under 1000 km/s. For example, the Andromeda Galaxy is approaching us at about 300 km/s. The relativistic effects of that proper motion are negligible, compared to the relative velocity between F0 and F1. So I'm simplifying the problem by saying that all galaxies are comoving relative to the expansion of space.
I haven't figured out how fast space is expanding in F1, or whether space is expanding equally in all directions in F1.
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"What's the formula to convert light-travel distance to luminosity distance."
I like the way you force me to look up definitions Phractality, I've looked at it before, but not from this aspect
Maybe this one will help? Luminosity and how far away things are. (http://zebu.uoregon.edu/~soper/Light/luminosity.html)
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(This one is for my own enjoyment Phractality, you know this. I remember looking a it from the question of how to define a standard candle some time ago, and also maybe helping those meeting this subject for the first time?)
But what it builds on are the concept of 'standard candles' (and geometry as I remember). A standard candle is defined as 'celestial objects with well-defined absolute magnitudes which are assumed to not vary with age or distance. Type I and II Cepheids and RR Lyraes are all examples". Stars who we assume to be of the same energy output, aka radiation, no matter where we find them.
"To help understand what is meant by standard candle, we first need to have a basic understanding of how distances are measured in astronomy. For small distances such as from the earth to the moon, lasers are used. Moving further out to Mercury, Venus or Mars, we use radar. Leaving our solar system and measuring to nearby stars, we use semi-annual parallax. And out to 500 parsecs (pc), spacecraft (e.g. Hipparcos) are used with measurements computed trigonometrically. We refer to these as direct methods of measurement. At distances greater than 500 pc, the error in the parallax measurement is too great and not usable. Indirect methods are used based on stellar properties such as luminosity,radii, the effective temperature and others. Distances are determined from relationships connecting these properties, including the period-luminosity relation for Cepheid variables. [Illingworth & Clark 2000]
While it is difficult to find a ‘pure’ definition for STANDARD CANDLE, reliable sources provide enough information to define it as saying there is no single object used for a Standard Candle; there are collections of stellar objects with known luminosities that allow them to be used to determine distances. The Standard Candle object used depends on the distance being measured. The brightest Cepheids, for example, can be seen out to about 60 megaparsecs (Mpc). For distances of 150 and 250 Mpc, red and blue supergiants can be used, respectively. For distances even greater, a galaxy’s HII region or brightness of its globular clusters are used. Beyond 900 Mpc, astronomers rely on supernovae. In all measurements, as the distance increases, the accuracy decreases. [Kaufmann & Freedman 1999, Illingworth & Clark 2000]"
From STANDARD CANDLES by RONALD E. MICKLE Denver, Colorado 80005 (http://www.denverastrosociety.org/dfiles/mickle/StandardCandles.pdf)
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Maybe this one will help? Luminosity and how far away things are. (http://zebu.uoregon.edu/~soper/Light/luminosity.html)
Not really. I'm referring to the fact that light-travel distance is c times the time it took for light to get here from where the object was before the space between us expanded. Luminosity obeys the inverse square law for how far away the object is after the space expanded. There are formulas for each, based on the Z (redshift) of the object. One formula is based on a constant value of H0; others use increasing or decreasing values of H0.
When the type of distance is not specified, it is usually the light-travel distance. The CMBR is believed to have taken 13.9 billion years to get here. It came from objects which are now much farther away. Since the expansion is a bit faster now, the Hubble limit is c/H0≈ 13.7 Gly. Light emitted, now, from anything more than about 13.7 Gly away can never get here. When you read about distances greater than that, you are probably reading about a luminosity distance.
There's also angular distance. Consider an object whose apparent angular width is θ. Consider the triangle formed by the observer at θ and the left and right sides of the object, The actual size of the object when the light was emitted is the opposite side of the triangle. The angular distance is the adjacent side of the triangle. If the object's actual size remains constant, its angular size will shrink. But we see it as it was before the angle shrank.
SIMPLIFIED EXAMPLE:
If it took 9 billion years for light from a supernova to reach us, the light-travel distance is 9 Gly. During that time, the distance between us and the source has doubled. (That's assuming the Hubble parameter has been constant at about 2.5 x 10^-18. I once worked out the time required to double distances, using logarithms on Wolframalpha.com. It takes 4.5 billion years to double areas and 3 billion years to double volumes.)
The angular distance is how far the source was when the light was emitted, before the distance doubled. I should be able to calculate that distance, but right now the integral calculus corner of my brain is on strike. I have a hunch it might be 9 Gly / √2 = 6.36 Gly.
The source is now twice as far as when the light was emitted; if my hunch is right, it is now 12.73 Gly away. That is the luminosity distance, because the perceived brightness falls off as the inverse square of that distance.
Note: I am not an authority on any of this. If you think you see an error, you could be right.
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Let me see if I get it right :)
Are you thinking of including the expansion in the calculations of where a celestial object should be, not where it appears to be according to the light we measure at each time? And then also consider how much the space would have 'expanded' under the time it took for that celestial object to get where its 'real position' should be? Meaning not the 'apparent one' when judging by the light itself.
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When it comes to a expansion I'm not sure what it means in form of 'time dilations & LorentzFitzGerald contractions' actually. The reasonable (most simple) approach to me is to treat this as any other 'motion'. But then we have the question if the expansion is accelerating. If it is then we should notice the 'gravity' changing, to fit relativity. And as far as i know the gravity measured has not changed?
So then we have the idea of a expansion being something belonging to 'space' and distinctly different from any ordinary type of 'motion'. If that is correct you can ignore a expansion for this as a guess. The whole idea of 'space' in 'motion' actually makes me head hurt.
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You could possibly, and, very possibly :) that is, argue that as a expansion has no preferred direction (in each point) those effects take themselves out? But that one???
Also it would need to assume that all time dilations are illusions ('time' does not exist) as I think, at a first look, as well as defining all relativistic effects to each point, relating itself to all other points in some skewed manner, if you get my drift. And this is of course pure speculation, and nowhere near anything mainstream.
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When it comes to a 'blueshift'?
I don't know at all, if a blue shift is definable from a expansion we need to assume some sort of interaction between a light quanta and 'space'. And if 'light' is a field, then the wave picture is not enough to explain it. Only if assuming that 'waves' is what create a 'field' and the 'excitations' we call 'photons' would it make sense to me. Assuming a 'field' and then thinking that this 'field' creates 'waves'? And then also define those waves as some better approach to the light-duality create a 'preferred frame' to me, and tells me nothing in the same time.
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When it comes to a expansion I'm not sure what it means in form of 'time dilations & LorentzFitzGerald contractions' actually. The reasonable (most simple) approach to me is to treat this as any other 'motion'. But then we have the question if the expansion is accelerating. If it is then we should notice the 'gravity' changing, to fit relativity. And as far as i know the gravity measured has not changed?
So then we have the idea of a expansion being something belonging to 'space' and distinctly different from any ordinary type of 'motion'. If that is correct you can ignore a expansion for this as a guess. The whole idea of 'space' in 'motion' actually makes me head hurt.
Yes; you could define a coordinate grid whose axes are like massless unstretchable tape measures, with origin at Earth. I, too, used to assume that was the "correct" and "obvious" way to do it. Distant galaxies would be racing away from the origin past the light-year markings on the tape. In such a coordinate system, the length contraction and time dilation of SR would apply to those galaxies. The farther your galaxy is from the origin, the slower your time would pass relative to clocks that are stationary relative to the tape measures, and vice versa. This would slow the expansion of space as you go farther from the origin.
There's nothing wrong with that type of coordinates, but mainstream cosmologists prefer comoving coordinates. As I said before, the coordinate axes are not like unstretchable measuring tapes. Instead, they are like measuring chains with unstretchable links, and new links are being added continually at the rate of 2.5 x 10-18/s. For every 4 x 1017 links, you add one link per second. The new links are sprinkled evenly so that the older links maintain their position relative to comoving inertial objects. Since there is no relative motion between the fixed galaxies and the measuring chains, the increasing distance from the origin is considered to be only "apparent". The galaxies are not length contracted or time dilated relative to comoving coordinates. Clocks fixed to the chains run at the same speed as clocks in nearby galaxies.
These are just two very different ways to define the mathematical space in which we measure physical space. Choosing types of space is like choosing log-log paper or lin-lin paper.
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Let me see if I get it right :)
Are you thinking of including the expansion in the calculations of where a celestial object should be, not where it appears to be according to the light we measure at each time? And then also consider how much the space would have 'expanded' under the time it took for that celestial object to get where its 'real position' should be? Meaning not the 'apparent one' when judging by the light itself.
I'm just saying that, when we speak of cosmological distances, we need to be explicit about which type of distance we mean.
P.S.: I'm liable to slip up in this regard. Kick me if I don't practice what I preach.
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Interesting reading you Phractality :) I'm thinking that an expansion, if existing, only relate to blue shifts, for now that is. If it does it becomes a statement of a geometry changing, and the geometry change being equal in all directions at each 'point'. Then we will either need to put a layer of 'waves' upon this geometry and describe it from that, or we will need to assume some deeper connection between light and space, aka a field. But a field is not waves, and it's not photons. It's a field, and what makes a field change is the arrow, not interactions per se. Interactions is a second hand effect to the idea of there being a arrow of time to me.
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When it comes to a 'blueshift'?
I don't know at all, if a blue shift is definable from a expansion we need to assume some sort of interaction between a light quanta and 'space'. And if 'light' is a field, then the wave picture is not enough to explain it. Only if assuming that 'waves' is what create a 'field' and the 'excitations' we call 'photons' would it make sense to me. Assuming a 'field' and then thinking that this 'field' creates 'waves'? And then also define those waves as some better approach to the light-duality create a 'preferred frame' to me, and tells me nothing in the same time.
The CMBR originated as black body radiation, which can be thought of as waves or particles. I don't think it matters which way you think of it for the present discussion. The photons were continuously emitted and absorbed until the plasma cooled to about 3000 K.
If you are stationary relative to the CMBR, you see the 3000 K radiation redshifted to about 2.7 K in all directions. If you are moving at .9682 c relative to the CMBR, you see is warmer to the front and colder to the rear.
According to Wolframalpha, the relativistic redshift for .9682 c is 6.867, and for -.9682 c, it is -.8729. I think that means that light frequencies of light from the front are 7.867 times as high as normal, and from the rear, .8729 times lower, i.e., 0.1271 times as high. So in frame F1, the CMBR today would have a color temperature of 21.24 K to the front and 0.343 K to the rear. Moments after the plasma became transparent, it might have had a color temperature of 23,600 K to the front and 381 K to the rear.
Note: The redshift of the CMBR in F0 is entirely due to the expansion of space, so there is no time dilation in comoving coordinates, and the non-relativistic redshift formula applies. The relative motion between F0 and f1 requires the relativistic redshift formula. This hurts my brain!
As for a preferred frame, the obvious choice is stationary relative to the CMBR. Our solar system is blueshifted in the direction of Virgo, indicating velocity in that direction of about 625 km/s. (Different sources give different speeds.) As mentioned before, if the plasma became transparent everywhere at the same time in that reference frame, then it could not have become transparent everywhere in any other reference frame. With relative motion in the x direction between two reference frames, events which are simultaneous in one frame are not simultaneous in any other reference frame. The SR transform formula is t' = γ(t - vx/c2).
Personally, I believe there is a substantive aether which is stationary relative to the CMBR. Except for the blueshift of the CMBR toward Virgo, we have no other way to detect motion relative to the aether. That will change if we ever prove the existence of FTL phenomena. But that's another discussion, entirely.
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Interesting reading you Phractality :) I'm thinking that an expansion, if existing, only relate to blue shifts, for now that is. If it does it becomes a statement of a geometry changing, and the geometry change being equal in all directions at each 'point'. Then we will either need to put a layer of 'waves' upon this geometry and describe it from that, or we will need to assume some deeper connection between light and space, aka a field. But a field is not waves, and it's not photons. It's a field, and what makes a field change is the arrow, not interactions per se. Interactions is a second hand effect to the idea of there being a arrow of time to me.
We can think of a space flag ship at the origin of F1, and a fleet of space ships comoving inertially with the flagship. For your fleet of space ships to maintain their proper relationship to the galaxies, F1 must be expanding. Comoving objects don't "accelerate" away from one another; the space between them just grows at an accelerating pace. I'm not yet sure how fast space is expanding in F1. I suspect that an observer in F1 would see his fleet of ships moving farther apart at the rate H1 = H0. I could be off by a factor of four, though. How does gamma affect the rate of expansion?
Yor_on, I don't know if you were up all night or got up early. It's nearly midnight, here, so I'm off to bed.
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K, that makes sense :) Although one thing, if you're discussing a time dilation/contraction too you must then specify relative what frame you define it. In this case it would be the CBR as I understand you? When it comes to F1 relative F0 you then should expect a similar blue and red shift for both, generally seen, as both then must relate their dilations etc to the cosmic background radiation. I think you need to go into why you need to define two different SpaceTime coordinates relative how those entities (F1 F0) move a little more for me to get it.
If you're assuming that the plasma cooled differently depending on relative motion/acceleration for those measuring I think you are correct, and if using the CBR as the 'preferred frame' defining it you will find each observer to have its own 'time scale', although all of them related through Lorentz transformations. It's tricky in that different uniform motions must bring with it different time dilations etc, relative what is measured locally. And there, as you point out, you also have relativistic blue shift which differs from normal blue shift (ambulance sound). Assuming you can ignore relativistic blue/red shift you can simplify it a little :)
But you need to define relative what you measure the effects as I think.
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K. it's been fun Phractality :)
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Light loses energy due to gravity at its origin,as it travels through space and away from its point of origin, this was predicted by general relativity, and proven by Radek Wojtak of the Niels Bohr Institute. The universe may in fact extend trillions of light years beyond the Hubbles field of view because the light from these distant objects loses most of its energy before it comes close enough to observe. CBR may in fact be the extent of the distance light can travel before it fades away, as objects beyond this limit would still emit radiation which travels farther than light due to the energy imparted at origin, Red shifting light has less energy than blue shifting light, ultraviolet, X-rays, and gamma rays have more energy than radio waves, microwaves, infrared, and visible light, and therefor travel farther.
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Nikstlitselpmur? Can you prove that light lose energy propagating? If you mean that it is frame related I agree but if you treat a light quanta in situ, then it never lose any energy. Better link up what you state there.
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Nikstlitselpmur? Can you prove that light lose energy propagating? If you mean that it is frame related I agree but if you treat a light quanta in situ, then it never lose any energy. Better link up what you state there.
yor_on
The phenomena is known as "cosmological gravitational redshift" here's the link,
http://dark.nbi.ku.dk/news/2011/light_from_galaxy_clusters/
'General relativity predicts that light should lose its energy when travelling away from the massive bodies. The group of Radek Wojtak of the Niels Bohr Institute at the University of Copenhagen collected data from 8000 galaxy clusters and found that the light coming from the cluster centers tended to be red-shifted compared to the cluster edges, confirming the energy loss due to gravity.' (wiki)
http://en.wikipedia.org/wiki/Gravitation
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That's gravity Nik :)
No different from the gravity well Earth is. Light will blueshift (according to a earth bound observer) falling in, and red shift going 'up' the gravity well. To assume a intrinsic energy loss will also introduce time for its intrinsic properties as well as interactions without annihilation. It's GR and gravity. You could possibly? think of it as if gravity in itself is a 'frame of reference' relative the light you observe. too much gravity and light coming out should from the observer outside a gravity well (black hole) 'die out' in its redshift, according to that observer and as a extreme example.
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If anyone can prove it otherwise I'm very interested :) but as far as i know the light disappearing from the far observers frame of reference will, in a thought up 'comoving' frame, or better expressed, 'at rest' with that light propagating, still be there, happily making its way.
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is it this one you're referring to? Gravitational Effects on Light Propagation. (http://www.mrelativity.net/GravitationEffectsOnLightProp/Gravitational%20Effects%20on%20Light%20Propagation.htm) I'm not sure if you can call that anything more than a hypothesis so far.
Found it at Millennium Relativity. "Millennium relativity is a new theory in relativistic physics that replaces Einstein's special and general theories of relativity. More than ten years of research into the accepted body of experimental evidence leads to the discovery of significant flaws in the underlying foundations of both relativistic and classical physics." and so it belongs to New Theories here, not mainstream physics, until validated by unique experiments proving a discrepancy with Relativity.
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K, that makes sense :) Although one thing, if you're discussing a time dilation/contraction too you must then specify relative what frame you define it. In this case it would be the CBR as I understand you? When it comes to F1 relative F0 you then should expect a similar blue and red shift for both, generally seen, as both then must relate their dilations etc to the cosmic background radiation. I think you need to go into why you need to define two different SpaceTime coordinates relative how those entities (F1 F0) move a little more for me to get it.
If you're assuming that the plasma cooled differently depending on relative motion/acceleration for those measuring I think you are correct, and if using the CBR as the 'preferred frame' defining it you will find each observer to have its own 'time scale', although all of them related through Lorentz transformations. It's tricky in that different uniform motions must bring with it different time dilations etc, relative what is measured locally. And there, as you point out, you also have relativistic blue shift which differs from normal blue shift (ambulance sound). Assuming you can ignore relativistic blue/red shift you can simplify it a little :)
But you need to define relative what you measure the effects as I think.
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K. it's been fun Phractality :)
The CMBR originated when all that matter existed as a hot plasma, and the plasma cooled to a about 3000 K, making it transparent. Soon after that galaxies formed, and they may serve to define the reference frame which I am calling F0. Essentially all the visible matter and dark matter in the visible universe appears to be approximately comoving relative to the CMBR. For the present discussion, we may ignore proper motions, such as the fact that Andromeda is approaching us at about .001 c. Since galaxies formed from the same matter which had produced the CMBR, and since momentum is conserved, I see no point in distinguishing between F0 and the reference frame of the CMBR. In terms of space-time, the CMBR is F0 at t = 0. (My F0 clocks are set to zero at the moment when the plasma in their vicinity became transparent. I understand it, that happened at about the same time everywhere in F0. Hence the extremely small observed variations in the color temperature of the CMBR.
Since the time transformation between F0 and F1 depends on the x coordinate, the plasma must have become transparent earlier at points with greater x values. So you can't synchronize all F1 clocks to the moment when the plasma became transparent. Instead, you can choose one value of x where F0 and F1 clocks were set to zero at the same instant.
As I (mis)understand it, the 2.7 K appearance of the CMBR is the redshifted 3000 K radiation from the hot plasma. That corresponds to z = -.9991. (Definition of z. (http://en.wikipedia.org/wiki/Redshift#Measurement.2C_characterization.2C_and_interpretation)) In comoving coordinates, relativity does not enter into the formula for z due to the "apparent" velocity due to expansion of space. The redshift of the CMBR is just the non-relativistic Doppler shift. So I guess light-travel distance to the source of the CMBR is increasing at .9991 c. (The relativistic redshift formula for z = -.9991 yields -.5997 c. Anyway, that's what I get from Wolframalpha.)
An observer passing Earth in F1 would be looking at the same CMBR we are, but it would be blueshifted in the direction of relative velocity. Since the relative velocity is real, you need to apply the relativistic z formula to the velocity of .9682 c. That is a combination of Doppler shift, length contraction and time dilation. Wolframalpha calculates that z = 6.867 (http://www.wolframalpha.com/input/?i=relativistic+redshift+v+%3D+.9682+c), which means the observed frequency is 7.867 times the frequency observed at the same location in F0, which would be a color temperature of 21.24 K. The same observer looking back would see z = -.8729 (http://www.wolframalpha.com/input/?i=relativistic+redshift+v+%3D+-.9682+c), so the observed frequency would be .1271 times that observed by Earthlings, for a color temperature of 0.343 K.
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That one was tricky :) and this one "Since galaxies formed from the same matter which had produced the CMBR, and since momentum is conserved, I see no point in distinguishing between F0 and the reference frame of the CMBR." even more so Phractality. Give me some time here to see what arguments I can come up with. You sure have thought about it :)
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You might find this interesting Phractality SimilarAGO.pdf (https://sites.google.com/site/scalinguniverse2011/self-similar-model/SimilarAGO.pdf?attredirects=0&d=1)
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That's gravity Nik :)
If anyone can prove it otherwise I'm very interested :) but as far as i know the light disappearing from the far observers frame of reference will, in a thought up 'comoving' frame, or better expressed, 'at rest' with that light propagating, still be there, happily making its way.
The energy contained in an electromagnetic wave is finite, not infinite. If energy is stripped from an electromagnetic wave by interaction with gravity, it follows that the EMW will eventually be depleted of energy after enough interactions.
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Light loses energy due to gravity at its origin,as it travels through space and away from its point of origin, this was predicted by general relativity, and proven by Radek Wojtak of the Niels Bohr Institute. The universe may in fact extend trillions of light years beyond the Hubbles field of view because the light from these distant objects loses most of its energy before it comes close enough to observe. CBR may in fact be the extent of the distance light can travel before it fades away, as objects beyond this limit would still emit radiation which travels farther than light due to the energy imparted at origin, Red shifting light has less energy than blue shifting light, ultraviolet, X-rays, and gamma rays have more energy than radio waves, microwaves, infrared, and visible light, and therefor travel farther.
Light from beyond the Hubble limit can never reach us because the distance between us and the source is increase faster than the speed of light. The CMBR that we see comes from stuff that was close to the Hubble limit when the plasma first became transparent.
Photons are like stretchable millipedes crawling toward one another at the speed of millipede relative to the surface of an expanding balloon. Each of the millipede's legs can only move at the speed of millipede relative to the surface of the balloon. As the balloon expands, the millipedes get longer (redshifted). The farther apart two ants are, the faster the distance between them is being stretched. There is a certain distance beyond which they can't get any closer together without exceeding the speed of millipede. That distance is the Hubble limit of the balloon.
In the present problem, we're not concerned with the effects of gravity. Photons are redshifted because they are stretched by the expansion of space. (The millipedes get stretched by the expansion of the balloon, not because they are crawling uphill.) The original big bang theory assumed that gravity was slowing the expansion because the universe was assumed to be finite in size. If the universe is homogeneous, isotropic and infinite in size, then the gravitational potential is the same everywhere, there is no uphill or downhill, and gravity does not resist the expansion of space.
X-rays and radio waves have the same Hubble limit. It is determined by the speed of light and the rate of expansion, not by the wavelength of the light. Once a photon is emitted, it may travel infinite distance in infinite time, but it will never get any closer to an observer who is beyond the Hubble limit.
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Nikstlitselpmur? Can you prove that light lose energy propagating? If you mean that it is frame related I agree but if you treat a light quanta in situ, then it never lose any energy. Better link up what you state there.
It is true that redshifted light light is received with less energy than it had when it was emitted. Where the redshift is due to a real relative velocity, the difference is just a matter of whose reference frame it is measured in. Light from a source in the Andromeda Galaxy is blueshifted due to the approach speed of .001 c. Those photons pack more energy in our reference frame than in Andromeda's reference frame.
If you are using inertial coordinates (unstretchable tape measures), rather than comoving coordinates (unstretchable chain links), you can say that our reference frame is moving away from the source of the CMBR, and the energy loss is a result of switching reference frames. In comoving coordinates, the increasing distance is called "apparent", and both the source and observer are in the same comoving reference frame. So a different explanation of the energy loss is required.
Is energy is conserved in comoving coordinates? Is the energy lost by redshifted photons matched by the energy equivalent of new space?
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yeah, but Nik is referring to gravitational blue and red shift, right? But even so your analogue might work Phractality as a gravitational potential indeed is a distorted topology according to relativity although it's the equivalence principle that steps in here. Anyway Nik, refute this and prove them wrong :) (http://xxx.lanl.gov/abs/physics/9907017) You will then have taken your first significative step towards a new definition, and possibly also redefining relativity.
There is another point that's confusing me here, easy to do I admit :) and as you say Phractality, I'm not that used to thinking comoving.
Assuming that everything made of matter is comoving, how does it do it? the answer should be gravity right? But in a expanding universe, assuming expanses opening between galaxies with different vectors, will this comoving principle still hold? If it does then the universe should need to perfectly isotropic and homogeneous, shouldn't it? And the comoving we see around our galaxy is already a approximative definition, as I understands it?
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BTW Nic, if you don't mind, what has your ideas to do with Phractality's? You saw something you thought of as a common nominator or? Was it the question for the thread??
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Nic, light escaping from a neutron star is redshifted quite a lot due to gravity, but all that happens in a short distance. If we're talking about light from a star close to a super-massive black hole, the redshift continues to increase to a somewhat greater distance from the black hole. Those are the rare and extreme cases. Once you get out of those really deep gravity wells, gravitational redshift is very minor. The gravity lens associated with some super clusters of galaxies is barely enough to produce Einstein rings. That's a far cry from the magnitude of the redshift associated with the CMBR. The CMBR comes from diffuse light sources before matter began to condense to form stars, galaxies, etc. So it did not have to climb out of any deep local gravity well.
Perhaps you are thinking of the theory that the expansion is driven by left over momentum from the big gang, and gravity is trying to pull it all back to the original singularity from which it originated. That idea stems from Newton's shell theorem, which assumes infinite empty space outside of the largest shell of matter. If the universe is infinitely large, then there is no largest shell and no emptiness beyond it. In that case, gravity pulls equally in all directions, not back toward the nonexistent singularity.
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BTW Nic, if you don't mind, what has your ideas to do with Phractality's? You saw something you thought of as a common nominator or? Was it the question for the thread??
Scientists are willing to change their theories to accommodate new evidence, Radek Wojtak presents new evidence, even Einstein had to change his theory of a static universe and Lambda to accommodate Hubble's observations.
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Yep, but he wanted a 'static universe' for philosophical reasons, it fitted also the observations at that time, around 1917 as I understand. Radek Wojtak present a hypothesis, and he need to find a way to prove it experimentally first as I see it, and making it present data that refutes the other definition.
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Light from beyond the Hubble limit can never reach us because the distance between us and the source is increase faster than the speed of light. The CMBR that we see comes from stuff that was close to the Hubble limit when the plasma first became transparent.
When Einstein first proposed his theories of general and special relativity he thought the Universe was static,(not expanding) in order to facilitate this he created what he called "Lambda" or the Universal Constant. However when Hubble provided proof that the Universe was in fact expanding in the form of red shifting, Einstein was forced to reconsider, and called it (Lambda) the biggest blunder of his career.As time progressed, astronomers and physicists realized that not only is the Universe expanding, the speed of expansion is increasing, so they devised their own Lambda, in the form of a Univerisal Constant, the ever increasing expansion at ever increasing speeds factor.
The Universe would appear identically the same if the point of observation was within the gravitational well of a Reissner-Nordström BH, yet in fact be static, and not expanding, merely the perception of expansion is observed because the observer is receding.
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That's true Nik, you can apply a receding/shrinking point of view towards us existing as matter, instead of defining it as a expansion, as they become mirrors of each other. Distance is a weird subject in relativity too. I've just reread Radeks hypothesis about light relating it to time dilations and I'm not sure what's so different with it compared to Einsteins treatment of it with 'clocks'? They will still only be a consequence of 'frames of reference' meaning always demanding relative comparisons between your local clock/ruler and some other frame? What exactly do you find different with it?
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That's true Nik, you can apply a receding/shrinking point of view towards us existing as matter, instead of defining it as a expansion, as they become mirrors of each other. Distance is a weird subject in relativity too. I've just reread Radeks hypothesis about light relating it to time dilations and I'm not sure what's so different with it compared to Einsteins treatment of it with 'clocks'? They will still only be a consequence of 'frames of reference' meaning always demanding relative comparisons between your local clock/ruler and some other frame? What exactly do you find different with it?
I'm not up to speed on this type of model. It sounds like a choice of how you define your standards of length and time. If your standard unit of length is defined as constant at the point of highest gravitational potential, like the middle of a cosmic void, then your meter stick at the bottom of a gravity well will be shorter in terms of that defined constant length.
The standards in use by mainstream science, today, are defined in relation to a constant speed of light and a physical standard (caesium atom emission) of wavelength/frequency. Those standards are defined as constant, regardless of where the caesium atom is located with respect to gravitational potential. The result is warped space-time. You could define space-time as flat, rather than warped, allowing gravitational potential to affect the wavelength/frequency of the caesium emission.
Another possibility would be to adopt the Hubble limit as a standard unit of length, making the visible universe a constant size. If the expansion of space accelerated, other units of length would grow longer in proportion to the visible universe.
People tend to regard their definitions as sacred cows. If somebody else worships a sacred goat, it's time for jihad!