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Old 2019-09-16, 07:43   #1
LaurV
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Default The expanding Universe and Big Bang theory...

Playing the devil's advocate here, following some posts in the "official news" and other "scientific" places here on the forum, related to the age of the universe...

What "proofs" or "facts" do we have of the expanding space/universe, except for the red shift? More clearly asked, is there any other experimental evidence, beside of the red shifts that supports the theory of the expanding space/big bang?

We have to say that we are totally tangent with the subject (read: ignorant), being neither physicist not "astronomist" (is the "astronomer" just a guy who names stars? like movie stars, whatever? hehe, this is for the devil's dictionary thread) and our knowledge is limited to "general public knowledge" and wikipedia, in the domain, but we were always puzzled by this question since we were in grade 7, and first heard about these things from the elementary physics classes, because if the only evidence is the red shifts, we may have an interesting explanation to it which does not involve space dilation.. (or... was it dilution?)

Joking apart, we know some people here have a real passion for (and knowledge about) astronomy. What their statement would be?

Last fiddled with by LaurV on 2019-09-23 at 08:52
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Old 2019-09-16, 09:35   #2
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Quote:
Originally Posted by LaurV View Post
is there any other experimental evidence, beside of the red shifts that support the theory of the expanding space/big bang?
Background microwave radiation.
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Old 2019-09-16, 09:49   #3
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Quote:
Originally Posted by LaurV View Post
is there any other experimental evidence, beside of the red shifts that support the theory of the expanding space/big bang?
Abundances of H, D, He-3, He-4, Li-6 and Li-7.
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Old 2019-09-16, 10:36   #4
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Ask a Wikipedia-Generation physicist, what is the age of the universe?
He will look it up and give you an absolute value for a Relative-Parameter and not even suspect any discrepancies.

https://en.m.wikipedia.org/wiki/Absolute_space_and_time
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Old 2019-09-16, 13:46   #5
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There is an aspect to redshift observations beyond the indication that the universe is expanding.

If memory serves, the fact that most quasars have fairly high red shifts mitigates against "steady state" models of the universe.

Last fiddled with by Dr Sardonicus on 2019-09-16 at 13:46 Reason: Insert omitted word
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Old 2019-09-23, 03:23   #6
LaurV
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Wow, take it easy, I am still trying to read and understand the information provided by Nick in post #2. In about half year I may move to Xilman's post #3.
These things are not very easy to grasp... I think my brain is very limited...

Last fiddled with by LaurV on 2019-09-23 at 03:24
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Old 2019-09-23, 07:40   #7
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Nah. It isn't an expanding universe. It is just that light is lazy (aren't we all?) and gets weaker as it ages (just like all of us).

But seriously, do gravity waves also "stretch" out a they travel? And just what is gravity anyway?
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Old 2019-09-23, 08:22   #8
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Nah. It isn't an expanding universe. It is just that light is lazy (aren't we all?) and gets weaker as it ages (just like all of us).

But seriously, do gravity waves also "stretch" out a they travel? And just what is gravity anyway?
The best theory of gravity we have at the moment is Einstein's general relativity. When applied to the universe as a whole there appears to be a need for his so-called cosmological constant term in the field equations.

In this theory, gravity is the term we use to describe the discrepancy between Lorentzian geometry and the physically observed geometry near a massive body.

In Lorentzian geometry, two neighbouring bodies of negligible dimensions and mass and bearing no electric charge (technical term: test particles) in free-fall which show no relative motion to each other will remain in that state. In non-Lorentzian geometry their separation and relative velocities change, even though neither of them feel any forces acting on them (that's what free-fall means). The changes are ascribed to a fictitious force called "gravity".

According to GR, everything stretches in an expanding universe, including space-time. As gravitational waves are variations in the metric of space-time, they necessarily stretch.

Last fiddled with by xilman on 2019-09-23 at 10:42 Reason: s/masses/particles/
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Old 2019-09-23, 09:24   #9
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Quote:
Originally Posted by xilman View Post
According to GR, everything stretches in an expanding universe, including space-time. As gravitational waves are variations in the metric of space-time, they necessarily stretch.
And naturally the follow up questions are: what is space, what makes it expand, and what is it expanding into.

I couldn't see any reference in the GW detection press reports about adjustments for the expected expansion. I'd guess such computations are used to help estimate the distance to the source.
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Old 2019-09-23, 10:13   #10
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Quote:
Originally Posted by retina View Post
And naturally the follow up questions are: what is space, what makes it expand, and what is it expanding into.

I couldn't see any reference in the GW detection press reports about adjustments for the expected expansion. I'd guess such computations are used to help estimate the distance to the source.
It isn't expanding into anything.
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Old 2019-09-23, 10:16   #11
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Quote:
Originally Posted by xilman View Post
It isn't expanding into anything.
We have no data to support such a conclusion AFAICT.

Last fiddled with by retina on 2019-09-23 at 10:17
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