Speed of the Sun: Facts & Measurements

[John Richard]

Hi,

Is it posible for us to determine the velocity of our sun?

The Hubble constant gives a referent for the exspansion of the universe but do we have any way of knowing if the point at the centre of the big bang was, (or is), stationary?

Do we know in which direction the centre of our universe was, (or is)?

I understand that we go through a very complex series of motions here on Earth, orbits round our sun, sun orbits galaxy, galaxy orbits other galaxies and on. So I appreciate that putting this in anything other than purely circumstantial language might be a bridge too far. but what is know of this?

In an expanding universe, I can understand the doppler shift of light in one direction due to the overlay of motion causing an increase in frequency, (please correct me if I am wrong), but a reduction in frequency would suggest motion opposing expansion.

Is this considdered to be a result of relative motion due to celestial dynamics?

Any help is greatly appreciated.

John

 

[chroot]

The universe has no center. The big bang happened "everywhere at once," and not at all like the explosion of a bomb in space already-extant space. A two-dimensional analogy is the expansion of the surface of a balloon while it is being inflated. The surface of a balloon also does not have a center.

The universe has no concept of absolute motion, so it's meaningless to ask what the absolute motion of the Sun is. If you provide some other reference point, a reasonable estimate of velocity with respect to it can be worked out, but it will not be of much use to you, or anyone else.

The fact that (essentially) every galaxy in the universe appears to be receding away from our own is an indication that the universe is expanding. Any observer in any other galaxy would observe the same thing: all other galaxies moving away.

- Warren

 

[John Richard]

Thank you for the reply.

I find it staggering that such missconceptions are allowed to propagate. Every single public reference to the big bang makes it seem that it started as a tiny micro-dot in one place. That it was all compressed together into one single point "in" time and space and then boom.

What it seems like you are trying to suggest is that there was no extention at all, prior to the big bang! That there was no precursor of anything at all!

No dimensions, even if void of any content, (I don't care about time). Is that what you are saying?

 

[chroot]

I find it staggering that such missconceptions are allowed to propagate. Every single public reference to the big bang makes it seem that it started as a tiny micro-dot in one place. That it was all compressed together into one single point "in" time and space and then boom.

The popular press is responsible for literally hundreds of staggering misconceptions in science. I'm not going to write a list, but several dozen pop into my head after only a moment of thought.

What it seems like you are trying to suggest is that there was no extention at all, prior to the big bang! That there was no precursor of anything at all!

That's correct. We currently have no idea what existed before the big bang, or what exists outside the universe. According to current understanding, these aren't even reasonable questions to ask. The answers may be physically unknowable, and may not be of any consequence for our own universe anyway.

No dimensions, even if void of any content, (I don't care about time). Is that what you are saying?

Space itself (at least, the space that comprises our universe) began with the big bang. There was no space before the big bang, nor did the big bang expand into some existing, enclosing space. At least, that's the current model.

- Warren

 

[John Richard]

Thanks Warren

Gob smacked

John

 

[russ_watters]

I find it staggering that such missconceptions are allowed to propagate. Every single public reference to the big bang makes it seem that it started as a tiny micro-dot in one place. That it was all compressed together into one single point "in" time and space and then boom.

So much of that is easy to misconstrue. Ie, if "it [the universe] was all compressed together into one single point" is generally correct. It's just that that point wasn't a point at the center of some void.

 

[EL]

"it [the universe] was all compressed together into one single point" is generally correct.

Well, at least if we're talking about the observable universe.

 

[tony873004]

I believe that the cosmic microwave background radiation is redshifted in one direction and blueshifted in another by an amount that reveals that we are moving about 600 km/s relative to something that would observe no red and blue shifts.

 

[chroot]

You are correct, Tony, but there's no reason to believe that reference frame, the comoving reference frame, is any more important than any other.

- Warren

 

[marcus]

Hi,

Is it posible for us to determine the velocity of our sun?

...

Yes, our sun has an absolute velocity with respect to what is called the "Hubble flow" and this has been determined fairly accurately by the COBE microwave background mapping satellite in the mid 1990s.

This is not what you were asking about, I suspect.

You were asking about expansionary motion. However there is no centerpoint of expansion.
We have no absolute recession velocity as part of universal expansion. Distant objects appear to recede from us as if we were the center. And from the standpoint of a distant object we would be receding. Everybody sees himself as the center, and there is no center.

this expansion is often called the "Hubble flow" and it gives a criterion for when something is STATIONARY with respect to it. If you are stationary then the recession of distant objects is symmetric, the same in all directions.

If you are moving with respect to the universal expansion, then objects ahead of you will not be receding so fast----they will seem to have a few km/second deducted from the speed they should have according to Hubble law. And objects astern of you will have a few km/second added to the recession speed that the law says they should have.

Hubble was aware of this in the 1930s, but it is a very slight thing to measure. Actually our sun is moving at about 370 km/second with respect to the universal expansion, in the direction marked in the sky by the constellation Leo.

Redshifted galaxies in that direction do not look quite as redshifted as they should, given their distance. Galaxies behind us (opposite Leo position in the sky) are slightly more redshifted. In other directions there is little or no effect.

Our sun has several velocities depending on what you take as standing still. It is circling the center of the Milkyway galaxy at a couple of hundred km/second. The galaxy is moving, our local group of galaxies is moving. But what I have told you is, in some sense, more absolute because it is 370 km/second with respect to the universe as a whole.

This speed was measured in the 1990s by the COBE team, when they found that the microwave background sky was just slightly warmer in the Leo direction (and colder in the reverse direction). they were able to pinpoint it, and to say rather precisely the solar system would have to be moving in order to cause that slight milliKelvin temperture difference.

If you want a link to the paper that they published about this in the mid 1990s let me know. I or someone will get it. If I remember the lead author was Charles Bennett.the expansion has no center. It is a largescale average increase distances between stationary objects---objects which are essentially not moving with respect to the Hubble flow or equivalently the CMB. Ignoring small random motions, basically stationary objects. The current rate of expansion of distance is about one percent every 140 million years.

 

[marcus]

I believe that the cosmic microwave background radiation is redshifted in one direction and blueshifted in another by an amount that reveals that we are moving about 600 km/s relative to something that would observe no red and blue shifts.

that is right, but it is not 600 km/second

If you are talking about the sun's motion relative to CMB, the speed is about 370 km/second.

If you are talking about the Milkyway galaxy, it's speed is higher. I recall something like 500-600 km/second.

the two vectors are in different directions because the sun also has orbital motion around the center of the galaxy. there is some cancelation too.

=======================

I see Chroot has already taken care of almost all the questions. I had to do something else halfway thru and didn't get my reply posted. So now I just basically agree with Warren, except possibly on some minor details (maybe he doesn't like the 370 figure or something.)

 

[John Richard]

Thank you Marcus.

I will search out Charles Bennett on the web but if you do come across the link that would be great!

Am I right then, in saying that the expansion is isotropic.

Can I consider the expansion as a scalar deflection of distance. (Expansion in proportion to the distances between the celestial bodies)?

John

 

[chroot]

Space expands everywhere at the same rate, as far as we know. The further two objects are from each other, the faster they will measure their speed of mutual recession. This is Hubble's law:

v = H_0 d

http://en.wikipedia.org/wiki/Hubble's_law

- Warren

 

[John Richard]

Thank you Warren

Marcus, I have found the following pdf:

First Year Wilkinson Microwave Anisotropy Probe (WMAP1) Observations:
Preliminary Maps and Basic Results

Big file with sky maps the lot, thank you

John

 

[John Richard]

I see from the WMAP data that CBM are isotropic and I can see how that points to a voidless origin. If the big bang had been in the manner of an explosion in space then CBM would point to that explosion.

What I am struggling to understand is why CBM don't interact with themselves.

Do we know anything of the evolution of CBM. Are there any conjectures or theories that look at changes in CBM over the life of the universe.

I think what I'm asking is, as the universe expands, is the wavelength of the CBM increasing?

I appreciate that this might be a little ambitious since I am guessing we have only really been studying it for the past 8 years. (It may also be implicit in the WMAP data in some way that I am over looking)

Any thoughts

Thank you.

 

[DaveC426913]

The popular press is responsible for literally hundreds of staggering misconceptions in science. I'm not going to write a list, but several dozen pop into my head after only a moment of thought.

I think the popular press is only partly to blame. The public take some responsibility for only caring to know as much as fits into a 20 second news clip. Things like the Big Bang and SR and GR simply can not be described in 20 seonds using every day concepts - especially without any foundation of knowledge to build on.

Too many people are too comfortable thinking about little electron moons orbiting proton planets...

 

[russ_watters]

Do we know anything of the evolution of CBM. Are there any conjectures or theories that look at changes in CBM over the life of the universe.

I think what I'm asking is, as the universe expands, is the wavelength of the CBM increasing?

Most of the rest didn't make much sense to me, but yes!, the CMB's wavelength increases as the universe expands. The wavelength of the CMB was predicted by a team of scientists while another team was discovering it.

 

[John Richard]

Most of the rest didn't make much sense to me, but yes!, the CMB's wavelength increases as the universe expands. The wavelength of the CMB was predicted by a team of scientists while another team was discovering it.

Thanks Russ,

The problem I'm having is with understanding how an isotropic wave system manages not to interfere with itself. I think it is a question about wave dynamics that I perhaps should ask over on the physics section.

Sorry, it was a bit wishy washy.

John

 

[John Richard]

I was just writing out a question about wave dynamics over on the general physics section when something occurred to me.

Is the entire universe beating as one, so to speak. Its pulse being the frequency of the CBM's? Is the entire background of the universe in harmony so that when the upper crest of a wave is detected in orbit around Earth, we can assume the upper crest will also be detectable over at Alpha Centauri?

As well as being isotropic, do the CBM's also posses spatial symmetry?

Thanks for your help

John

 

[russ_watters]

The CMB isn't a single uniform, phase-synchronized wave, it is random noise centered around a particular frequency. It works pretty much like the light we see from the sun (the universe was at one time an opaque clump of hot matter). It's a hot object with a bell-curve shaped spectrum of light, centered around a particular frequency.

 

[John Richard]

Thank you Russ

Back to studying wave dynamics I think!

 

[W3pcq]

I may be wrong, but as it seams to me that the nature of cosmology itself may be to blame for the many misconceptions. The biggest misconception of all is the idea that the current model is accurate. It seams that the big bang is a semi far fetched impossible to prove model which has been deemed the mainstream guess.

I don't think people should believe anything cosmology claims as truth. The farthest that the truth goes in cosmology doesn't take you very far in conclusions. The details, like what was before the big bang, if there there even was a big bang etc are all speculation. What we know is that about 50 or so observed galaxies, out of more than we even know exist, are becoming farther apart. Throw in the cosmic background radiation, and they have made a model trying to explain every detail.

It is like having 2 blank red pieces of 1000 piece puzzle and claiming to think that the puzzle is of the chinese flag.

If you notice misconceptions in the media, that is because it is highly likely that the majority of what you here from cosmologists are misconceptions.

One possible reason is, that the conclusions must be stretched to get public interest. What they should do if they want to be true to the people, is they should show only the facts and evidence and go more in depth with it. I don't see why they give us only the speculation and don't go into detail on what is fact and observable.

Here is a simple deductive logic example.

If X is impossible to conceptualize,
And X is conceptualized,

The product will me a misconception

 

[chroot]

I don't think people should believe anything cosmology claims as truth.

No scientist would ever suggest that you should accept a model as absolute truth -- it's just a model, nothing more, nothing less. In time, it will be replaced with a different or more complete model that will answer more questions.

What we know is that about 50 or so observed galaxies, out of more than we even know exist, are becoming farther apart. Throw in the cosmic background radiation, and they have made a model trying to explain every detail.

Redshifts have been measured for thouuuuuuuuuusands of galaxies. And you really think that's all the evidence involved? You really underestimate those pesky scientists, don't you?

http://www.talkorigins.org/faqs/astronomy/bigbang.html

One possible reason is, that the conclusions must be stretched to get public interest. What they should do if they want to be true to the people, is they should show only the facts and evidence and go more in depth with it. I don't see why they give us only the speculation and don't go into detail on what is fact and observable.

You do understand that scientists publish evidence, analyses of evidence, expose holes in the arguments of others, and debate about open questions every single day right? What you're looking for is a journal. Perhaps you should try going to your local university library and pulling out a few to see how scientists talk among themselves. Everything you seek and more will be provided therein. You seem to be pretty ignorant of the entire process of science, so I suggest you select and begin regularly reading a few journals before making such statements again in public. They're a little, well, embarrassing.

- Warren

 

[W3pcq]

I'm sorry, I didn't mean to offend anyone. It isn't the fault of the scientists, it is the fault of the field that I was talking about. I know that the scientists working in the field of cosmology are no doubt very smart people who are doing great work. The problem is that they are in a very hard field which will always be a theoretical field. Everyone loves to think that they have figured out the secret of the universe, but it is ignorant for someone to think they have. On television cosmologists act as if they have and take it way too far. People tend to believe what scientists say, and when you have scientists claiming they know how the universe began, know that there was a beginning to time, that the universe is 13 billion years old, that the universe was once an infinately dense point etc., people tend to think they must be right. The way that cosmology is presented to the public it is almost starting a cult of people who believe in the model with faith. Like I said before, to be true to the people, more of the specs and details should be made public in the media and less of the speculation. I know that scientific journals are made public, and I am sorry if I seamed to include journals. I also think that you guys at physics forums are great and if it wasn't for you, then the misconceptions would run wild. I am very gratefull to be able to ask the scientists on this forum about my misunderstandings. Again it is the media that I have a problem with.

 

[chroot]

On television cosmologists act as if they have and take it way too far.

Which cosmologists have you seen on TV? I can't even think of a single example of a cosmologist who has made a TV appearance.

People tend to believe what scientists say, and when you have scientists claiming they know how the universe began, know that there was a beginning to time, that the universe is 13 billion years old, that the universe was once an infinately dense point etc., people tend to think they must be right.

There is a vast preponderance of evidence in favor of the big bang model. Similarly, there is a preponderance of evidence for Newton's law of gravity. Are either of these theories absolutely right, or beyond suspicion? No.

You're "preaching to the choir," W3pcq -- no scientist worth his salt will tell you that he or she has all the answers, or knows any of our models to be absolutely right.

The reason I'm being gruff with you is because your argument (scientists think they have all the answers, but they're just pompous because they obviously don't know everything yet) is a recurring strawman argument. The conclusion assumes the premise -- your conclusion only makes sense if scientists really do think they have all the answers, but you'll never meet a single scientist, ever, who will ever say any such thing. Even if TV popularizations and textbooks sound authoritative, no scientists anywhere will claim to have all the answers. Not only would that counter the scientific method and the spirit of scientific endeavor, it's demonstrably false. We know our theories are incomplete.

The way that cosmology is presented to the public it is almost starting a cult of people who believe in the model with faith.

Is it? Do you have some evidence to support this claim?

Like I said before, to be true to the people, more of the specs and details should be made public in the media and less of the speculation.

Journals are public. Any university library will let anyone who desires to walk in and spend as much time as they want reading them. If you're talking about the tripe that's published in USA Today or sound bites on CNN, well, remember that those are not produced by scientists! They're produced by people with degrees in english or communication, and they're trying to water down the topic into a format that's immediately accessible to everyone, including school children. It's almost impossible to imagine a non-scientist trying to explain, say, string theory to a sixth grader in a way that wouldn't make a real string theorist cringe. To be frank, they're also in the business of selling newspapers or recruiting advertising dollars, not the business of properly educating the public. We'd all love it if the news media made the effort to improve the quality of their depictions of science, but it would be far easier to simply direct eager people to better sources of information.

Again it is the media that I have a problem with.

The popular news media is not the appropriate place to obtain deep scientific knowledge! You simply cannot learn science from human interest pieces in the variety section of the Sunday newspaper. Try to find better sources, and you will no longer be so concerned.

- Warren

 

[W3pcq]

I get your point and I am very sorry if my posts have been offensive and bitter. I suppose my beef is not with you, but is with the History Channel, and the discovery channel. You would think that the History channel would be more respectable.

People I talk to who only watch shows on TV about cosmology have the way wrong idea as far as I'm concerned, and I think that the majority of the US population who listens to them get the wrong idea as well. Most christians I meet now believe in the big bang model and incorperate it into their religion. "There was nothing and then god made everything.", they say. People who are not religious who I talk to accept it and feel as if they now know where we came from. I know the news media is not a good source of science, but it is an excellent source of propiganda.

 

[DaveC426913]

Brian Greene's 'The Elegant Universe' the TV show was so resounding a disappointment after the book that I turned it off halfway through.

TV is not a learning device, it's an entertainment device.

If people want to learn aboujt cosmology, they'll pick up a book. As for those for don't pick up a book to learn, what weight would you give their opinion anyway?

 

[John Richard]

If people want to learn aboujt cosmology, they'll pick up a book. As for those for don't pick up a book to learn, what weight would you give their opinion anyway?

Well said DaveC.

I had a misconception about the big bang theory when I first came to this forum. On reflection, I have to admit that this stemmed from my lazyness and nothing else. Luckily, I joined the Physics Forum, and I'm not lazy anymore!

In the UK we have Sir Patrick Moore, he's as old as the universe and we love him. He does a monthly show called, The Sky at Night, which is like a regular update on exploration work. As far as I am aware, he has only ever pointed out the results of work done and I would defend his program highly. He got me interested enough to come seek out help.

Science, all of science, is the only opportunity we have for real understanding. The rest is mostly untestable conjecture.

 

[W3pcq]

As for those for don't pick up a book to learn, what weight would you give their opinion anyway?

That isn't really the problem. The problem is that some kids grow up watching it and their opinions are formed. Later some of them become fascinated with physics and want to learn. The danger is that when they start, they might try and build the science around the model and that is backwards. Starting with iffy assumptions can start you off in the wrong direction. You need to learn the facts before you make assumptions. Starting off with assumptions and looking for facts that support the assumptions isn't the best way to learn.

Another thing is that often people getting into physics start by trying to conceptualize things that may not even be true. Trying to wrap your head around things that are impossible to wrap your head around isn't very productive. You do all this reading and thinking and in the end your still just left with a blown up balloon with dots or a sheet and a bowling ball. The fact is that these analogies are misconceptions themselves if you take them seriously.

Another thing that bugs me is the way people seems hostile if they don't agree with you on speculative issues. It is just like the way religions work. People have to agree or they are uncomfortable. What good does it do to have this need. We should just all agree on the observable facts and then leave the theoretical aspects free for individual thought. Making mass agreements on things just makes progress slower. Since the beginning of written history people have made mass assumptions and we all know how suppressive they can be. How long did it take for Copernicus to get people to listen when he said that the Earth revolved around the sun? Challenging the mainstream in mans history has proven to be dangerous.

 

[rbj]

I believe that the cosmic microwave background radiation is redshifted in one direction and blueshifted in another by an amount that reveals that we are moving about 600 km/s relative to something that would observe no red and blue shifts.

You are correct, Tony, but there's no reason to believe that reference frame, the comoving reference frame, is any more important than any other.

wow. i didn't know that about the CMB radiation and, although i had not previously believed in an aether (and i still don't), i am intrigued that the reference frame that is coincident with the CMB is not any more important than any other. it surely seems to have a unique and universal claim.

that is right, but it is not 600 km/second
If you are talking about the sun's motion relative to CMB, the speed is about 370 km/second.

yeah, you guys, can you explain why the the unred-shifted CMB would seem to be moving relative to the center of our galaxy without a notion that our galaxy is moving relative to some universal frame of reference that can me measured by anyone else in the universe?

 

[John Richard]

That isn't really the problem. The problem is that some kids grow up watching it and their opinions are formed. Later some of them become fascinated with physics and want to learn. The danger is that when they start, they might try and build the science around the model and that is backwards. Starting with iffy assumptions can start you off in the wrong direction. You need to learn the facts before you make assumptions. Starting off with assumptions and looking for facts that support the assumptions isn't the best way to learn.

Another thing is that often people getting into physics start by trying to conceptualize things that may not even be true. Trying to wrap your head around things that are impossible to wrap your head around isn't very productive. You do all this reading and thinking and in the end your still just left with a blown up balloon with dots or a sheet and a bowling ball. The fact is that these analogies are misconceptions themselves if you take them seriously.

If your misconceptions made you interested enough to learn then they did you a favour. If you had no misconceptions what would you need to learn? Analogies, by there very nature, are not that which they are seeking to explain. This is really a debate for the philosophy section, but reading your post I would say you have unearthed the fact that you may have had, or may still have the wrong ideas. Congratulations, you've just justified the process of learning.

 

[John Richard]

wow. i didn't know that about the CMB radiation and, although i had not previously believed in an aether (and i still don't), i am intrigued that the reference frame that is coincident with the CMB is not any more important than any other. it surely seems to have a unique and universal claim.



yeah, you guys, can you explain why the the unred-shifted CMB would seem to be moving relative to the center of our galaxy without a notion that our galaxy is moving relative to some universal frame of reference that can me measured by anyone else in the universe?

O good, back to the question. I may be wrong but I think this has to do with the nature of the observational isotropy of the speed of light. The frequency of light can only be affected by its source. Once propagated any observer will observe the finger print of the velocity of the light source. The observers motion does not affect this.

So effectively we can calculate the speed of the light source with reference to the universal speed limit which is C. Then we can cross reference with other observed motions to arrive at a topology of interrelated motions.

Happy to be shot if I'm wrong!

John

 

[W3pcq]

If your misconceptions made you interested enough to learn then they did you a favour. If you had no misconceptions what would you need to learn? Analogies, by there very nature, are not that which they are seeking to explain. This is really a debate for the philosophy section, but reading your post I would say you have unearthed the fact that you may have had, or may still have the wrong ideas. Congratulations, you've just justified the process of learning.

That is a good point, but I think that my argument still stands. That goes back to what I said earlier about how conclusions must be stretched to gain public interest.

I can't speak for anyone but myself, but I feel that the misconceptions in the media have been destructive to my interest in learning. I agree that some, and I would have no idea about percentages, go into physics trying to understand misconceptions on tv. Me, I have a natural curiosity about how things work and what is out there. The misconceptions in the media have only made me fustrated. The misconceptions in the media also may lead one to believe that all the mysteries have been solved, so what is the point.

I don't think that anyone has the right ideas when the idea is a speculation. If you would claim that the big bang model is the exact right idea, I would disagree. Maybe best educated guess, but nothing more.

 

[marcus]

that is right, but it is not 600 km/second
If you are talking about the sun's motion relative to CMB, the speed is about 370 km/second.

yeah, you guys, can you explain why the the unred-shifted CMB would seem to be moving relative to the center of our galaxy without a notion that our galaxy is moving relative to some universal frame of reference that can me measured by anyone else in the universe?

our galaxy IS moving relative to a universal frame that could be determined by anyone else. there is an absolute standard of rest which Hubble already knew about in the 1930s.
one can define what it means to be at rest with respect to the Hubble flow

the Hubble law v = HD is not exactly right because the solar system is moving 370 km/s in the direction of Leo. that means recession velocities of galaxies in that direction are not quite as high as they should be according to v = HD
and recession speeds of galaxies in the opposite direction from Leo are just slightly higher than they should be. Redshift data has always needed to be corrected for the Earth and sun's motion relative to the Hubble flow.

then when CmB data started coming in it just CONFIRMED this and allowed the solar system velocity to be measured more precisely, both speed and direction coordinates.

this doesn't have to do with AETHER as i understand it. Maybe you call it aether but I don't. It is just the uniform expansion (the Hubble flow). you can be at rest with respect to it or not. if you are moving relative to it then it will not be uniform or isotropic.

 

[marcus]

... The frequency of light can only be affected by its source. Once propagated any observer will observe the finger print of the velocity of the light source. The observers motion does not affect this.
...

What you say seems to be at odds with what is generally taught in college physics. Something's odd, either factually or in your use of terminology.

As ordinarily understood, BOTH the observer's motion and the expansion of distances affect the frequency of the light.

I'll illustrate with an example. In the case of thermal radiation, temperature gives a good handle on frequency because they are proportional. You know that the CMB was emitted from partly ionized gas at a temp of about 3000 kelvin and its temperature now is about 2.76 kelvin

Distances expanded by a factor of about 1100 during the time the light was traveling. The redshift is NOT A DOPPLER EFFECT and was caused by the stretching out of distances.

The gas that emitted the CMB light (which at the time was part visible part infrared, like from a 100 watt bulb) was about 40 million LY from our matter when it emitted the light.

It was receding from us at a speed of about 60c (sixty times the speed of light).

Today, that same matter, whose light is just now reaching us as CMB, is about 45 billion LY from us, and receding at a speed of 3.3c (slightly over three times the speed of light).

The redshift, which has reduced the frequency by a factor of 1100, is entirely attributable to the fact that while the light was traveling on its way to us cosmological distances increased 1100-fold.

the only doppler effect involved is a few MILLIkelvin caused by the Earth and sun motion of 370 km/second in the Leo direction.

You may have noticed that 1100 is the approx. ratio between the two distances I mentioned, the 40 million LY (distance then) and 45 billion LY (distance now)

Ooops, bedtime. don't have time now to discuss more. Anyway after some light is emitted, its frequency can be changed a lot by things that happen subsequently and also by the observer's motion (which in this case has only a small millikelvin effect but can have a larger one)

 

[W3pcq]

Is the doppler effect of EM radiation compatible with C according to special relativity?

 

[Janus]

Is the doppler effect of EM radiation compatible with C according to special relativity?

The standard Doppler effect equation has to be modified to a relativistic form, but the basic concept of the Doppler effect remains the same.

 

[marcus]

Is the doppler effect of EM radiation compatible with C according to special relativity?

The standard Doppler effect equation has to be modified to a relativistic form, but the basic concept of the Doppler effect remains the same.

To expand on what Janus said, the Doppler equation in Special Relativity (which only works for speeds less than c) says that the frequency ratio is
\sqrt{\frac{c-v}{c+v}}

Here v is the speed of the emitter relative to the receiver, and positive v denotes increasing distance. You can see that if v = 0.5c then the frequency ratio is
\sqrt{\frac{0.5}{1.5}} = 0.58
That means that the frequency of the received light is only 58 percent of the frequency of what was sent.

If you think in terms of wavelengths, they get longer and the formula is just the reciprocal. In astronomy the wavelength ratio can be written 1+z, so you might see this equation for a Doppler shift
1+z = \sqrt{\frac{c+v}{c-v}}

the point that needs emphasis IMO is that these Special Relativity formulas do not work for calculating the cosmological redshift.
In the case of redshift, the recession speeds are often greater than c, and the formulas break down in that case.
So in a beginning astronomy class you get taught a different formula for the redshift which does not depend on velocity.
1+z = \frac{a(t_r)}{a(t_e)}
Here t_e is the time the light was emitted and t_r is the time it was received. The a(t) is the scale factor at time t. The ratio is the factor by which the universe expanded during the time the light was in transit.

 

[John Richard]

What you say seems to be at odds with what is generally taught in college physics. Something's odd, either factually or in your use of terminology.

It was receding from us at a speed of about 60c (sixty times the speed of light).

Today, that same matter, whose light is just now reaching us as CMB, is about 45 billion LY from us, and receding at a speed of 3.3c (slightly over three times the speed of light).

Marcus, thank you for your reply. I think I was just factually wrong and I appologize to rbj.

Sometimes, stating what you think you know, gets a better answer than any question you may have asked. That is certainly true for me in this case.

You speak of speeds in excess of C and of CMB just reaching us and this makes it clear to me that I have a big gap in how I'm interpreting the big bang model. I understand that the CMB wave length will stretch as a result of the expansion. But, I am under the impression that we were inside the big bang, which means that the CMB will have to have been around us from the start.

I am also under the impression that nothing travels faster than light and that all points of observation will measure light at the same speed. I had assumed therefore, that the CMB that is around us is phase shifted from origin by a measure of light years equal to the time since the big bang. That the expansion has effected only the frequency.

I do not think it is fair of me to press on your time just to teach me. I would be very grateful if you could suggest some reading that might clear up my misconceptions.

Once again, thank you for taking time to help me.

John

 

[marcus]

... which means that the CMB will have to have been around us from the start.
...

Yes that is right! Caveat, we are talking about the mainstream picture here. there is a lot of evidence that it is right as far as it goes.

To get used to visualizing standard cosmology it can help enormously to play around with a cosmology calculatory. Several people here at PF have made their own----Jorrie, hellfire and I don't know who else. there are some threads where they discuss features.

but most of us use online java calculators by Ned Wright or Siobhan Morgan.
Go here
http://hubblesite.org/newscenter/archive/releases/2008/08/full/
http://scienceblogs.com/catdynamics/2008/02/liveblogging_the_high_redshift_1.php

It talks about a young galaxy at redshift z = 7.6 (if confirmed) observed as it was 12.8 billion years ago during the first wave of star formation
this is conference news, it hasn't been published yet AFAIK

So suppose you want to know the recession speed of a galaxy at z = 7.6
First try Ned Wright's
http://www.astro.ucla.edu/~wright/CosmoCalc.html
just plug in 7.6 for z, over on the left

what I get from Wright's is that the light travel time was 12.97 billion years which is a little off from the 12.8 they say in the press release but small discrepancies don't matter here. and I get that the age of the universe when the light was emitted was 0.7 billion years. Is that what you get?

the important thing to notice is over on the left Ned Wright puts in the default values of H=71, and Omega_matter = 0.27 and Lambda = 0.73. they are accepted parameter values, widely used. So when you go on to Morgan's calculator you should take them along with you and plug them in too. Morgan wants her students to work more and consciously put them in.

So then go here
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
and over on the left, put in 0.27 for matter, 0.73 for Lambda, and 71 for Hubble.
Then type 7.6 into the z box and see what you get. You should get some recession speeds!

Cosmology is largely non verbal. It is applying a mathematical model to the geometry of the universe, and fitting it to many different kinds of data.
That mathematical model is built into Wright's and Morgan's calculators.
When you play with those calculators you are playing with the best model of the universe we have today.

Truly enormous amounts of data of many different kinds are used to challenge the model. it must fit to the data. that is how the numbers 0.27, 0.73 and 71 are determined. The more data, the more accurate these estimates get, and the better the fit.

What do you get for the speeds? I get about 3.3c and 2.3c. 3.3c is the recession speed of the galaxy THEN when it emitted the light (some 12.8 billion years ago) and 2.3c is the recession speed NOW as the light is arriving to us and coming down the telescope.

The distance now should be greater than the distance then by a factor of 1+z which is 8.6.

How about checking to see if that is about right? 1+z is the factor by which the light wavelengths are stretched, so it must be the factor by which distances expanded in the universe while the light was in transit to us. If the ratio doesn't work out right, please tell me!
==========================
I gathered a bunch of useful links here:
https://www.physicsforums.com/showthread.php?p=1610331#post1610331

 

[AstroLiv]

I think I previously posted this comment wrongly:

Hi Marcus,

Do you have any idea where can I find a good multimedia, or other interaction to well understand the Solar Dopplergrams? I have difficulty answering the following question:

At about what speed is the right edge of the sun moving away (receding) from us at the equator?

Thank you in advance for your help.

Liv.