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Author Topic: How do we account for the expansion of Universe?  (Read 1060 times)

Offline Claire Rejuso

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How do we account for the expansion of Universe?
« on: 20/05/2016 03:33:56 »
Does the universe really expand? What are the theories that support the expansion of the universe?
« Last Edit: 20/05/2016 22:51:45 by chris »


 

Offline PmbPhy

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Re: Theories about the expansion of universe
« Reply #1 on: 20/05/2016 03:54:21 »
Quote from: Claire Rejuso
Does the universe really expand? What are the theories that support the expansion of the universe?
Welcome to the forum. :)

There is a great deal of evidence which is consistent with proposition that the universe is expanding. Theories don't support the expansion of the universe but rather our observations of an expanding universe is consistent with the model of cosmology of the expansion of space. Does that help?
 
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Offline Claire Rejuso

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Re: Theories about the expansion of universe
« Reply #2 on: 20/05/2016 04:52:48 »
Thanks! :) Can you please site some of those evidences?
 

Offline timey

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Re: Theories about the expansion of universe
« Reply #3 on: 20/05/2016 11:57:16 »
A 'theoretical' physicist will tell you that there is no direct evidence that the universe is expanding.
What a theoretical physicist will tell you is that the universe expanding is a theory that is consistent with observation in relation to interpretation and the mathematics of our current best working hypothesis.
The theoretical physicist will tell you that although our best working hypothesis is indeed our best understanding of our universe, that redshift and the dilation of the geometry of space is 'just' a hypothesis despite the fact that redshift is consistent with observation in relation to the maths of our best working theory.

I write this because Pmb Pete has perhaps slightly given the impression that the observational evidence of the expansion of the universe is a proven fact in relation to the theory, and this is misleading as the expansion of the universe is, despite the mathematical fit, just a hypothesis and not a proven fact.

If you want to understand what is and is not proven concerning our best working theories on how the physics of the universe work, then I recommend a book by Lee Smolin 'The Trouble with Physics'.  This is an incredibly concise book written with both the physicist and the ley person's requirements of understanding in mind, and shows exactly where current physics considerations fall short of a complete explanation, where alternate theories are considered and also fall short, and basically illuminates exactly how much it is that physicists 'do not' know about the physics of the universe.
 

Offline PmbPhy

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Re: Theories about the expansion of universe
« Reply #4 on: 22/05/2016 04:51:58 »
Quote from: timey
I write this because Pmb Pete has perhaps slightly given the impression that the observational evidence of the expansion of the universe is a proven fact in relation to the theory, and this is misleading as the expansion of the universe is, despite the mathematical fit, just a hypothesis and not a proven fact.
I gave no such impression whatsoever. In the future please don't put words into my mouth. Time after time in this and all other forums where I post I've explained that there is no such thing as proof in physics. In  this case I clearly said There is a great deal of evidence which is consistent with proposition that the universe is expanding. Just because existing evidence is consistent with a proposition it can't be taken to imply that the proposition is correct.

Also its misleading to say things like "just a hypothesis" because it gives laymen the idea that any hypothesis is just as good as any other hypothesis. That's why laymen don't trust science. In this case the hypothesis is substantiated by observation. That observation comes in the form of cosmological redshift. If the universe is expanding then the distance that galaxies are away from us will have a certain cosmological redshift, not just any cosmological redshift. That data is in the scientific literature. However I'm not an experimental physicist so you'd have to contact a place like the Harvard Smithsonian Center for Astrophysics and ask them for the data.
 

Offline evan_au

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Offline puppypower

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Re: How do we account for the expansion of Universe?
« Reply #6 on: 23/05/2016 11:51:38 »
Couldn't a speeding up of time create the same red shift, as an expansion of space? Both time and space are changing at the same time; space-time. A wave can be tweak by means of wavelength or frequency. For example, the pitch of the whistle on a train moving away will lower; Doppler shift. This is connected to space. The same pitch change can be made by the conductor tweaking the pitch of the whistle; train stationary.

In terms of a physical affect, a frequency led modulation of space-time could be caused by mass expanding; explosion. Currently we use dark energy to expand space-time, with dark energy never actually seen in the lab. That raises a yellow flag. On the other hand, one can easily do experiments altering the mass density, as a way to alter local space-time. If you pull the mass apart, with space not changing, you will get space-time expanding.

Another way to do this, that is common in nature, is stellar fusion and mass burn. The mass burn causes the mass of stars to decrease over time. The loss of energy; emitted radiation, from the star, results in a net expansion of local space-time. This could explain expansion relative to galaxies.
 

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Re: How do we account for the expansion of Universe?
« Reply #6 on: 23/05/2016 11:51:38 »

 

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