Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: MikeS on 01/09/2011 07:01:39
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Why do we believe space itself is expanding as opposed to things moving further apart in space.
What is the difference?
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One reason to believe that the background is expanding rather than objects are moving in an static background is that this would require objects to move through space at superluminal speeds. A second reason would be that what ever force (which is proportional to the distance in space) is driving this accelerated expansion would be likely to dilute if objects were moving through space and the expansion should slow ; however if the expansion is through the creation of more space then the expansion can remain proportional to the distance which agrees with observations.
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One reason to believe that the background is expanding rather than objects are moving in an static background is that this would require objects to move through space at superluminal speeds. A second reason would be that what ever force (which is proportional to the distance in space) is driving this accelerated expansion would be likely to dilute if objects were moving through space and the expansion should slow ; however if the expansion is through the creation of more space then the expansion can remain proportional to the distance which agrees with observations.
I can see that if objects are moving apart in space then whatever is driving the expansion is being diluted but I don't understand how the creation of more space stops the dilution. Can you explain that please?
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Or does this assume that whatever the driving force is, is a product of space itself and is therefore being created by the production of space?
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Imatfaal explanations are very good. The best way to see it is in 2D with a stretching rubber sheet or an inflatable ball. Before, observations was best modeled by a uniform stretching. Now, with dark energy, the stretching rate is linear. But we look to the past and we don't have a unified theory yet, so i doubt the official timeline of the universe is near perfection...
Imatfaal, do you know on what bases they say without expansion of space there would be superluminous speed of objects? Timeline? I never saw an absolute proof of that... I wonder...
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Imatfaal explanations are very good. The best way to see it is in 2D with a stretching rubber sheet or an inflatable ball. Before, observations was best modeled by a uniform stretching. Now, with dark energy, the stretching rate is linear. But we look to the past and we don't have a unified theory yet, so i doubt the official timeline of the universe is near perfection...
What is the difference please between 'uniform' and 'linear'? I assume linear means there is no stretching ('fabric [rubber sheet] is being added.)
Are you saying that dark energy is being produced at the same time as space is being produced?
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Yes, according to the actual model. Expansion increases linearly with distance. The farther apart two galaxies are, the higher is the rate of expansion between them. But no people has really measured an acceleration yet... Dark energy comes from observations of higher expansion than linear, correct my mistake...
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Would it be fair to say that the observed cosmological red-shift is wholly attributed to the Hubble law which means that the Universe is expanding and that expansion is accelerating?
This view has created the following problems
The expansion is superluminal.
What is driving the expansion.
To overcome the superluminal problem, it is assumed that space is being created (whatever that means).
Dark energy (whatever that means) has been thought up to explain the cause of the expansion.
Dark energy to stop it from being diluted is assumed to be created with the creation of space.
These aren't little adjustments to the basic theory, they seem to be of major importance but they seem to be little more than assumptions that in themselves create more questions and problems.
Is this a fair assessment?
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Would it be fair to say that the observed cosmological red-shift is wholly attributed to the Hubble law which means that the Universe is expanding and that expansion is accelerating?
No. There is other evidence - if the universe was static we would expect to see a certain time line as we looked further away, but we see a more accelerated change; events that we expect are further away and dimmer than would be predicted in a static sold state or simply expanding universe.
Remember that dark energy is a catch-all term for all the explanations that could drive universal accelerated expansion and that the cosmological constant is by no means agreed upon
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Space expands in conjunction with man's mental understanding/probe of certifiable data. Analogously, life comes from the pleasure of an orgasm but thereafter its work to stay alive & not so fun so to preserve survival.........
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Would it be fair to say that the observed cosmological red-shift is wholly attributed to the Hubble law which means that the Universe is expanding and that expansion is accelerating?
No. There is other evidence - if the universe was static we would expect to see a certain time line as we looked further away, but we see a more accelerated change; events that we expect are further away and dimmer than would be predicted in a static sold state or simply expanding universe.
Remember that dark energy is a catch-all term for all the explanations that could drive universal accelerated expansion and that the cosmological constant is by no means agreed upon
Thanks but that isn't actually what I asked. What I asked was,"is the observed cosmological red-shift wholly attributed to the Hubble law". In other words, is the Hubble expansion the only thing that is considered to make up the observed red-shift.