Jonathan

Physics Question

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Jonathan, I meant do you think we see an expansion looking through telescopes?

Ellen

Okay, then, as I said, no, my animations were not meant to accurately portray the universe's rate of expansion (just as I'm sure that Larry's envisioning of an expanding balloon and your raisin loaf example were not meant to portray it). But I do think that if we were to set up a telescope in reality, point it at any galaxies which are moving away from us, and shoot time-lapse images, we'd see the "shrinking" effect when those images were shown in sequence. Not being a physicist, I don't know how long of a period of time we'd have to cover with our time-lapse recording to get visually noticeable "shrinkage." Perhaps years? Perhaps decades?

J

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Another empirical falsification of this version of the shrinking theory: the observed redshift of galaxies would be independent of the distance. The distance between the centers of the galaxies would remain the same, the only increase in distance would be due to the simultaneous shrinking of any two galaxies, independent of the mutual distance of their centers. In fact the redshift increases with increasing distance, so this theory is not correct.

But what of an observer on the shrinking arm of a galaxy observing a star on the shrinking arm of another galaxy? Could a redshift be observed?

I didn't say that you wouldn't observe a redshift, shrinking galaxies would in general result in some change in distance, but independent of the distance between the centers of those galaxies, and moreover, in one half of the cases the change would be a decrease in distance (if the observers are sitting on the relatively distant arms of those galaxies), so you'd see as much blueshifts as redshifts.

Thanks, DF. It seems so obvious now!

And thanks everyone else for your input. I've actually learned a lot from this thread, and I appreciate your comments. It's been stimulating.

J

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Just a minute: who, reputable whom, is claiming the universe is not expanding and why?

--Brant

not heard of it

sorry to have missed this conversation's nuance

That is in fact what this whole discussion is about. I suggest you start to read the thread from the beginning.

Please, I've read the thread and just reread the first 20 posts, you can at least read my one sentence question carefully enough to properly answer it. That Einstein once imagined a constant universe is irrelevant; he's been dead over 50 years. That there is a shrinking universe model is just a theoretical point for conjecture or exploration as far as I can tell apropos this discussion. The "tired light" guys seem esoteric. All mainstream physicists seem to be riding the BB horse or at least the expanding universe horse.

--Brant

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> All mainstream physicists seem to be riding the BB horse or at least the expanding universe horse.

There seem to be three theories: 1. The horse is expanding and need to go on a diet. 2. The horse is shrinking and may need to be sold before it can no longer support the weight of its cowboy owner. 3. The horse is tired and slowing down. (My theory).

Plus a variant of 1: The horse once expanded at near light speed billions of years ago and has now aged and cooled down and is expanding more slowly.

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[...] I do think that if we were to set up a telescope in reality, point it at any galaxies which are moving away from us, and shoot time-lapse images, we'd see the "shrinking" effect when those images were shown in sequence. Not being a physicist, I don't know how long of a period of time we'd have to cover with our time-lapse recording to get visually noticeable "shrinkage." Perhaps years? Perhaps decades?

Perhaps a couple centuries to get barely noticeable "shrinkage" with the nearest galaxies with current telescopic resolution -- if Larry did the calculation correctly (without, for instance, making some error on the order of factors of 10) talking it through out loud while he was driving (me as passenger) to an eye doctor's exam. I gather that the distances being enormous, the angle of change in the image would be minute. (For 1 megaparsec, he got 1 - 10^9 change in the angle, over a century, if I'm reporting correctly.)

Ellen

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> All mainstream physicists seem to be riding the BB horse or at least the expanding universe horse.

There seem to be three theories: 1. The horse is expanding and need to go on a diet. 2. The horse is shrinking and may need to be sold before it can no longer support the weight of its cowboy owner. 3. The horse is tired and slowing down. (My theory).

Plus a variant of 1: The horse once expanded at near light speed billions of years ago and has now aged and cooled down and is expanding more slowly.

Current observations indicate that the cosmos is expanding and at an accelerating pace. That is one of the big Cosmology Surprise of the last ten to fifteen years. The Cosmos is stranger than we have imagined.

Ba'al Chatzaf

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> Current observations indicate that the cosmos is expanding and at an accelerating pace.

Make sure your head doesn't explode.

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> Current observations indicate that the cosmos is expanding and at an accelerating pace.

Make sure your head doesn't explode.

You might want to have a look at this:

http://www.eso.org/~...rs/EPN/epn.html

and this:

http://www.supernova.lbl.gov/PhysicsTodayArticle.pdf

The more we find out about the cosmos, the stranger it gets.

Ba'al Chatzaf

Edited by BaalChatzaf

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I gather that[,] the distances being enormous, the angle of change in the image would be minute. (For 1 megaparsec, he got 1 - 10^9 change in the angle, over a century, if I'm reporting correctly.)

Ahem, I think it was 1 - 10^9 over two centuries.

The details of the calculation sequence are fuzzy to him by this point as well as to me. It was a complicated sequence, done verbally on the fly (or on the drive), and used approximations to make the math easier.

Net result he got, though, was that it would take longer than a centenarian's life to discern even a little shrinkage in time-lapse photos of telescopic images of galaxies.

Ellen

Edited by Ellen Stuttle

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I gather that[,] the distances being enormous, the angle of change in the image would be minute. (For 1 megaparsec, he got 1 - 10^9 change in the angle, over a century, if I'm reporting correctly.)

Ahem, I think it was 1 - 10^9 over two centuries.

The details of the calculation sequence are fuzzy to him by this point as well as to me. It was a complicated sequence, done verbally on the fly (or on the drive), and used approximations to make the math easier.

Net result he got, though, was that it would take longer than a centenarian's life to discern even a little shrinkage in time-lapse photos of telescopic images of galaxies.

Ellen

It doesn't surprise me that it would take that long to get barely noticeable shrinkage.

Thanks for putting Larry's brain on it, and for sharing the results.

J

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Again, each blob represents a galaxy, or if you prefer, millions of them. In this case, however, each shrinks in size but maintains its position in space in relation to the others.

My question is this: If in both scenarios, we are basically a tiny speck on one of the blobs, how would we determine which of the two scenarios represented what we were observing from within the system?

If, in the second scenario, we and the instruments that we used to observe and measure relationships were "shrinking" along with everything else, how would we establish that the universe was not expanding, but that we were actually "shrinking" and only misinterpreting the universe as expanding?

J

The shape of spacetime is described by something called a metric tensor. The shape of spacetime explains gravitational effects, but extremely simple modifications to the metric tensor explain the spatial expansion of the universe.

Matter and radiation in general relativity is described by a mathematical object called a stress-energy tensor. Making everything shrink in such a way as to reproduce the observations would require fine-tuning every single physical system in the universe. There is no simple modification you could make to the stress-energy tensor of a universe to explain the data, as far as I know.

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One of the major questions asked by those who first believed in an expansionary universe was precisely yours: If big bang caused expansion outwards, when and if will gravity take effect and pull the universe again into a tiny ball. Moreover, what's the proof that this isn't happening?

The answer is that objects coming towards us will bend light towards the blue of the spectra.

EM

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One of the major questions asked by those who first believed in an expansionary universe was precisely yours: If big bang caused expansion outwards, when and if will gravity take effect and pull the universe again into a tiny ball. Moreover, what's the proof that this isn't happening?

The answer is that objects coming towards us will bend light towards the blue of the spectra.

EM

That is really a Doppler, not gravitational lensing.

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Again, each blob represents a galaxy, or if you prefer, millions of them. In this case, however, each shrinks in size but maintains its position in space in relation to the others.

My question is this: If in both scenarios, we are basically a tiny speck on one of the blobs, how would we determine which of the two scenarios represented what we were observing from within the system?

If, in the second scenario, we and the instruments that we used to observe and measure relationships were "shrinking" along with everything else, how would we establish that the universe was not expanding, but that we were actually "shrinking" and only misinterpreting the universe as expanding?

J

The shape of spacetime is described by something called a metric tensor. The shape of spacetime explains gravitational effects, but extremely simple modifications to the metric tensor explain the spatial expansion of the universe.

Matter and radiation in general relativity is described by a mathematical object called a stress-energy tensor. Making everything shrink in such a way as to reproduce the observations would require fine-tuning every single physical system in the universe. There is no simple modification you could make to the stress-energy tensor of a universe to explain the data, as far as I know.

You don't appear to be grasping the system that I described in my initial post.

J

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One of the major questions asked by those who first believed in an expansionary universe was precisely yours: If big bang caused expansion outwards, when and if will gravity take effect and pull the universe again into a tiny ball.

That's not the question that I asked. My question was not about universal expansion versus universal contraction, but about how what appears to be universal expansion might being misidentified when it may actually fully or partially include something akin to discrete condensation/evaporation.

Moreover, what's the proof that this isn't happening?

The answer is that objects coming towards us will bend light towards the blue of the spectra.

Yes, that proves that my "condensation" proposal can't replace the expansion model, but it doesn't prove that "condensation" is not occurring in conjunction with expansion. Galaxies might be moving away from us at a proper expansionary constant while also discretely "condensing."

The fact that the initial post on this thread illustrated, for the sake of argument, two extremes as opposites does not mean that they must be opposites, or that they are mutually exclusive of each other.

J

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You don't appear to be grasping the system that I described in my initial post.

J

Here's a simplified visual representation of the Big Bang and the expansion of the universe:

Each blob represent a galaxy, or if you prefer, millions of galaxies. Whatever. The blobs maintain their size but move away from each other.

Here's a simplified visual representation of a different event:

Again, each blob represents a galaxy, or if you prefer, millions of them. In this case, however, each shrinks in size but maintains its position in space in relation to the others.

My question is this: If in both scenarios, we are basically a tiny speck on one of the blobs, how would we determine which of the two scenarios represented what we were observing from within the system?

If, in the second scenario, we and the instruments that we used to observe and measure relationships were "shrinking" along with everything else, how would we establish that the universe was not expanding, but that we were actually "shrinking" and only misinterpreting the universe as expanding?

J

You're moving the goalposts.

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You're moving the goalposts.

No, I'm not.

As I wrote here:

Well, my illustrations are only meant as extreme scenarios which isolate the relevant issues. The blobs wouldn't necessarily have to be perfectly stationary in the second clip. I only made them that way in order to focus on the problem of perspectives.

This thread isn't a game in which opponents try to win or to "move the goalposts" so that others can't win. I didn't create it to be adversarial, but to explore possibilities by illustrating expansion versus condensation via extreme examples. They were extreme for the sake of clarity. But you appear to be hellbent on fighting and winning, and therefore misidentify what the discussion is about.

J

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> Current observations indicate that the cosmos is expanding and at an accelerating pace.

Make sure your head doesn't explode.

Specifically the space between galaxies appears to be expanding. Your head is safe for the moment.

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> Current observations indicate that the cosmos is expanding and at an accelerating pace.

Make sure your head doesn't explode.

Specifically the space between galaxies appears to be expanding. Your head is safe for the moment.

The accelerating rate of expansion is what got me thinking about different ways of looking at what we measure, and I then starting this thread to begin exploring possibilities. The questions that popped into my head were, "Why is acceleration considered unusual and unexplained in the case of the universe's expansion? Is it because expansion from an explosion center normally involves deceleration after the initial bang? If so, is there any possibility that we are misinterpreting the effects of something else as expansional acceleration, like, say, the rate of galactic condensation?"

After all, just thinking intuitively based on our current knowledge of how the physics of systems work, gravitational compression/condensation is usually associated with acceleration: the closer one gets to a massive object, the faster one will accelerate.

J

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> Current observations indicate that the cosmos is expanding and at an accelerating pace.

Make sure your head doesn't explode.

Specifically the space between galaxies appears to be expanding. Your head is safe for the moment.

The accelerating rate of expansion is what got me thinking about different ways of looking at what we measure, and I then starting this thread to begin exploring possibilities. The questions that popped into my head were, "Why is acceleration considered unusual and unexplained in the case of the universe's expansion? Is it because expansion from an explosion center normally involves deceleration after the initial bang? If so, is there any possibility that we are misinterpreting the effects of something else as expansional acceleration, like, say, the rate of galactic condensation?"

After all, just thinking intuitively based on our current knowledge of how the physics of systems work, gravitational compression/condensation is usually associated with acceleration: the closer one gets to a massive object, the faster one will accelerate.

J

Explosions on earth encounter two drag coefficients that cause deceleration. Namely, resistance from atmospheric gas and gravity.

OTH, Big Bang obeys the law of general relativity, which requires acceleration per equation. In this sense, general relativity describes a situation in which the observer is not priveleged to know the inertial fram of reference. In other words, in as much as gravity accelerates so does every other cause of motion...

EM

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