Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: FredL on 17/01/2012 02:00:54
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After listening to January 8th's podcast, it appears to me that Dominic does not subscribe to the theory that the universe is accelerating as it continues to expand. If there is sufficient energy available to overcome the intergalactic gravitational forces, why should there be insufficient energy to overcome the intragalactic gravitational forces?
Somewhere, (probably on the Naked Scientists' show) I recently heard that, due to the acceleration of the universe, galaxies will eventually disappear from view, because they will have reached (or exceeded) the speed of light, relative to us. I don't know which galaxies were observed to come to the conclusion that the universe is expanding and accelerating. But, according to the web site: http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN, the age of the universe is 14 billion years but the most distant observable objects are 47 billion years distant. However it is expressed, it seems to me that the evidence of acceleration is some billions of years old and there is no way to know what has occurred to the objects observed in that time. For all we know, or can know, they have reversed their acceleration and are speedily catching up with the energy they emitted billions of years ago.
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After listening to January 8th's podcast, it appears to me that Dominic does not subscribe to the theory that the universe is accelerating as it continues to expand. If there is sufficient energy available to overcome the intergalactic gravitational forces, why should there be insufficient energy to overcome the intragalactic gravitational forces?
I would be surprised if he didn't - but as I havent heard that podcast yet I cannot say for sure. On the issue of intra/inter galactic forces - it is just a matter of forces and distances. Galactic Clusters are a long way apart from each and the gravitational attraction is very low - the galaxies within clusters are close enough that background expansion is a smaller matter and that gravity is a more important factor.
Somewhere, (probably on the Naked Scientists' show) I recently heard that, due to the acceleration of the universe, galaxies will eventually disappear from view, because they will have reached (or exceeded) the speed of light, relative to us. I don't know which galaxies were observed to come to the conclusion that the universe is expanding and accelerating. But, according to the web site: http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN, the age of the universe is 14 billion years but the most distant observable objects are 47 billion years distant. However it is expressed, it seems to me that the evidence of acceleration is some billions of years old and there is no way to know what has occurred to the objects observed in that time. For all we know, or can know, they have reversed their acceleration and are speedily catching up with the energy they emitted billions of years ago.
No - but we try and postulate the simplest model that agrees with all the facts. until accelerated expansion (dark energy) was thought of we just used simplish mechanics to describe the universe, now it is a bit more complicated with the need to explain acceleration other than that caused by gravity. Your last sentence is a bit unclear - but suffice it to say that nothing massive catches up with light
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If I understand the OP correctly, in his last statement he is suggesting that it is possible that the universe has indeed stopped expanding and is contracting. Thus his reference to "catching up" to the light that we see now, which started heading our way billions of years ago.
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No - but we try and postulate the simplest model that agrees with all the facts.
The fact is that we can't know what's happening right now. We can only know what has happened X years ago with X being the amount of light years between us and the observed object.
If we look at a distant earth like planet (say Keppler 22b) and we had the technology to insta-travel there, it's quite possible that there's nothing left of the planet due to a huge asteroid impact or star explosion or whatever..
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No - but we try and postulate the simplest model that agrees with all the facts.
The fact is that we can't know what's happening right now. We can only know what has happened X years ago with X being the amount of light years between us and the observed object.
If we look at a distant earth like planet (say Keppler 22b) and we had the technology to insta-travel there, it's quite possible that there's nothing left of the planet due to a huge asteroid impact or star explosion or whatever..
Its possible that lots of things have happened - but we ignore them and take the simplest explanation that fits the facts
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Imatfaal
You say
"take the simplest explanation that fits the facts"
As regards the expanding universe, this seems to be mostly based on the Hubble expansion. It requires dark energy to make it work, something that has never been seen and may only exist in the minds of certain people in an effort to justify the standard model.
Time speeding up within the universe would look the same and requires nothing new to be added. This seems to me to be by far the simplest explanation. Ocams razor etc.
I believe you will say there is no universal time but I have yet to see a convincing argument to justify that.
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Imatfaal
You say
"take the simplest explanation that fits the facts"
As regards the expanding universe, this seems to be mostly based on the Hubble expansion. It requires dark energy to make it work, something that has never been seen and may only exist in the minds of certain people in an effort to justify the standard model.
no - the expanding universe is the balance or imbalance between residual velocity and mutual gravitational attraction; it is very simple theoretical stuff.
dark energy is only needed to explain the ACCELERATED expansion.
Time speeding up within the universe would look the same and requires nothing new to be added. This seems to me to be by far the simplest explanation. Ocams razor etc.
I believe you will say there is no universal time but I have yet to see a convincing argument to justify that.
A well worked (ie mathmatically coherent) use of time to explain the accelerated expansion would be great - the use of time to explain all expansion/all redshifting needs to also explain why the background isn't expanding (cos if all the red-shift is explained through your time-notion then the galactic clusters cannot be in relative motion and the big bang is clearly false). this is all quite apart from the universal time problem.
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imatfaal
I would not suggest that time dilation alone is the explanation for the observed Hubble shift, only that it could make a significant contribution.
As regards the expansion of space on the large scale but not on the small scale. The expansion is only observed on distances many orders of magnitude larger than the galactic scale. This could be due to a mixture of things. Maybe the orders of magnitude difference makes it impossible to observe accurately enough the red shift difference on a local scale. Maybe it is a relativistic effect. Light approaching the Earth is gravitationally red-shifted. Likewise light approaching our Galaxy is gravitationally red-shifted. Light approaching our Local Cluster is gravitationally red-shifted. To get an accurate picture all of this need to be taken into account. The question is has it been taken into account and if so how was it calibrated in the first place and could this calibration be wrong. My understanding is there is little that can be used to calibrate (judge distance) the red-shift other than type 1A Supernova. A large recent survey seemed to indicate that their apparent brightness did not match their red-shift and it was suggested 'one way' of accounting for the discrepancy was that 'time' passed slower in the past (the other of course being that space is expanding).
http://www.newscientist.com/article/dn13792-cosmic-time-warp-revealed-in-slowmotion-supernovae.html
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Mike - why is light approaching any massive body/bodies gravitationally red-shifted?
And that article does not support your assertion.
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imatfaal
This is what I said
"A large recent survey seemed to indicate that their apparent brightness did not match their red-shift and it was suggested 'one way' of accounting for the discrepancy was that 'time' passed slower in the past (the other of course being that space is expanding)."
This is a quote form the above mentioned article
"Once upon a time, time was different. Supernova explosions in the early universe appear to age more slowly than today's supernovae, as if time itself was running slower back then, according to a recent series of astronomical observations. This cosmic time warp is exactly what should be produced by the expansion of the universe, confirming conventional big bang theory."
http://www.newscientist.com/article/dn13792-cosmic-time-warp-revealed-in-slowmotion-supernovae.html
Mike - why is light approaching any massive body/bodies gravitationally red-shifted?
And that article does not support your assertion.
Although the article believes the effect to be due to cosmic expansion it does point put that there is another explanation, that time ran slower in the past.
I will get back to you on this point.
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MikeS
Quantum theory is dependent on space, be it atomic or galactic, being a perfect void through which light, neutrinos, masses, fields etc travel.
However according to an eBook I just read called ‘me-flow’ magnets spin space into vortexes around their long axes. North poles have clockwise magnetic faces and south poles anticlockwise ones. Magnets with like spin attract etc.
Fields accordingly are a construct of flowing space which if stationary or moving does not affect the speed of light. Yet giving space any property poses the possibility that it might infinitesimally affect the wavelength of light which would only become apparent on beams which have travelled gianormous inter-galactic distances.
:)
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The ancient Hindus had the belief that the universe expands and contracts in, and expands again in cylces.
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The ancient Hindus had universities and algebra, and made an observatory with exact maths, that due to earth movement, is about 15 degrees off. If I remember rightly.
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Can we avoid answering questions on the physics board with spiritual/mystical explanations please?
Thanks