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Is there any evidence for the Big Bang?
06-09-2017, 09:49 AM
Post: #1
Is there any evidence for the Big Bang?
In other words, is it a theory or a hypothesis?

I could only name the Background Radiation. But it did not originate at the "Big Bang" but some 100 000 years "later", when the energy density of the universe has become low enough to allow atomic nuclei to form. Is there any evidence for what happened before or is it mere extrapolation?
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06-09-2017, 10:29 AM
Post: #2
RE: Is there any evidence for the Big Bang?
(06-09-2017 09:49 AM)Avun Jahei Wrote:  In other words, is it a theory or a hypothesis?

I could only name the Background Radiation. But it did not originate at the "Big Bang" but some 100 000 years "later", when the energy density of the universe has become low enough to allow atomic nuclei to form. Is there any evidence for what happened before or is it mere extrapolation?

There's more than only background radiation - e.g. the existence of light elements, and Hubble's Law. There's even more evidence I think, but I would have to do some reading first Smile

It's thus considered a theory, not a hypothesis. All this evidence points to (indeed by extrapolation) a singularity as the starting point.

Don't cling to a mistake just because you spent a lot of time making it
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06-09-2017, 10:54 AM
Post: #3
RE: Is there any evidence for the Big Bang?
How does the existence of light elements point to a singularity as a starting point? And how do we even know that a singularity can physically exist when all known laws of physics break down as soon as we reach Planck density?
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06-09-2017, 11:06 AM
Post: #4
RE: Is there any evidence for the Big Bang?
Avun, picture a square-shaped circle. You can't do it. Knowledge, reason, and concepts are limited to the parameters of the human mind. It is essential, yea, vital to understand that you can not present the infinite into the finite, especially considering that all structures soever are finite by definition. Dissolution in silence gives the best representation of what is within the parameters of the human mind.

..
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06-09-2017, 11:10 AM
Post: #5
RE: Is there any evidence for the Big Bang?
(06-09-2017 11:06 AM)IMtM Wrote:  Avun, picture a square-shaped circle. You can't do it. Knowledge, reason, and concepts are limited to the parameters of the human mind. It is essential, yea, vital to understand that you can not present the infinite into the finite, especially considering that all structures soever are finite by definition. Dissolution in silence gives the best representation of what is within the parameters of the human mind.

What does that have to do with my question if there is physical evidence for the Big Bang?
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06-09-2017, 11:13 AM
Post: #6
RE: Is there any evidence for the Big Bang?
(06-09-2017 11:10 AM)Avun Jahei Wrote:  What does that have to do with my question if there is physical evidence for the Big Bang?
Apparently nothing. I apologize. Smile

..
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06-09-2017, 01:42 PM
Post: #7
RE: Is there any evidence for the Big Bang?
(06-09-2017 10:54 AM)Avun Jahei Wrote:  How does the existence of light elements point to a singularity as a starting point?

They don't, and that's not what I said.

Their abundance can only be satisfactorily explained by assuming a big bang event.

(06-09-2017 10:54 AM)Avun Jahei Wrote:  And how do we even know that a singularity can physically exist when all known laws of physics break down as soon as we reach Planck density?

Seems you know more about singularities than I do Wink

What I found on Wiki however is that beyond the Plack density we simply don't have the equations to model the universe's evolution.

Don't cling to a mistake just because you spent a lot of time making it
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06-09-2017, 02:01 PM
Post: #8
RE: Is there any evidence for the Big Bang?
(06-09-2017 10:54 AM)Avun Jahei Wrote:  How does the existence of light elements point to a singularity as a starting point? And how do we even know that a singularity can physically exist when all known laws of physics break down as soon as we reach Planck density?

Actually the singularity refers to the division by zero that appears in the equations of General Relativity when the volume reaches zero. In Quantum Theory one might say that the universe started as a Planck volume and avoid the singularity. But GR and QT do not play nice together when it comes to talking about space-time.

The biggest clue to there being something corresponding to a Big Bang is that the universe is expanding. Working backwards, one comes to the conclusion that it all started from a single point a finite interval of time ago. The discovery that the universe looked differently in the distant past (e.g., quasars) and the detection of the predicted Cosmic Microwave Background argued strongly against the competing Steady State theory. I remember all of this happening in the 1960s. Smile

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06-09-2017, 04:13 PM
Post: #9
RE: Is there any evidence for the Big Bang?
I don't know about 'evidence', but there was a documentary on it not too long ago and it specifically touched on the subject of the Big Bang Theory.

When someone asks "What would Jesus do?" remind them that flipping tables and chasing people with a whip is entirely possible.
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06-09-2017, 10:07 PM
Post: #10
RE: Is there any evidence for the Big Bang?
(06-09-2017 02:01 PM)Imprecise Interrupt Wrote:  
(06-09-2017 10:54 AM)Avun Jahei Wrote:  How does the existence of light elements point to a singularity as a starting point? And how do we even know that a singularity can physically exist when all known laws of physics break down as soon as we reach Planck density?

Actually the singularity refers to the division by zero that appears in the equations of General Relativity when the volume reaches zero. In Quantum Theory one might say that the universe started as a Planck volume and avoid the singularity. But GR and QT do not play nice together when it comes to talking about space-time.

The biggest clue to there being something corresponding to a Big Bang is that the universe is expanding. Working backwards, one comes to the conclusion that it all started from a single point a finite interval of time ago. The discovery that the universe looked differently in the distant past (e.g., quasars) and the detection of the predicted Cosmic Microwave Background argued strongly against the competing Steady State theory. I remember all of this happening in the 1960s. Smile

Yes, but all this evidence only suggests that the universe once was very hot and dense. But how hot and dense? I just do not understand how we can possibly know that something like a Quark epoch or a Hadron epoch ever occurred. As far as I understand it is all extrapolation and that can hardly count as evidence.

The Big Bang theory was established before we discovered that most of the universe consists of something we know nothing about (dark matter, dark energy). Considering that shouldn't we be very cautious in making any assumptions about the distant past of our universe?
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