Questions about the Big Bang

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I was under the impression that red shift indicated speed they are moving away from us.
Actually, the best way of thinking of the redshift is that it tells by what factor the universe expanded between the light being emitted and us detecting it.

The more distant they are, the faster they are receding, so it amounts to the same thing.
No, it doesn't. Distance is not determined from redshift; it is determined by a separate set of observations, and there is a lot of work that goes into making the determination. See Ned Wright's page on this here:

http://www.astro.ucla.edu/~wright/distance.htm

This is as far as I know based on irreffutable evidence rather than a theory.
Don't overstate. Our current hot big bang model is well-supported, yes, but evidence is hardly ever "irrefutable" in science; there is always some chance that our best current models could be wrong.
 
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OK Peter, I don't doubt the possibility that new models will be found which are more accurate than those we now have.
As long as the data not change I will still be able to sleep at night.
 
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There is no particular direction where the redshift is more or it is less.
Therefore we conclude either that
A: There is no center from which galaxies are spreading out, they are all just getting further away from each other.
or
B: Earth is the center of the Universe, and everything began spreading out from here.
Well, I could mention again that if you fire a shotgun over calm water, you will see where the pellets land in the water and it will tell you something about an explosion. The pellets all get further and further away from each other as they travel. So increasing distance between entities doesn't prove expansion.

But I was just reading about red shift and the article said that the redshifts of galaxies include both a component related to recessional velocity from expansion of the Universe, and a component related to "peculiar motion" (Doppler shift). Ok! That could conceivably settle all this, -maybe. But how is the redshift component due to expansion identified and distinguished from redshift due to doppler? Or is this all theory and the portion of redshift that is to be attributed to each cause just guesswork?
 
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Actually, the best way of thinking of the redshift is that it tells by what factor the universe expanded between the light being emitted and us detecting it.
What about the Doppler component? Can the two components be reliably identified and quantified for any specific galaxy?
 

Drakkith

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Well, I could mention again that if you fire a shotgun over calm water, you will see where the pellets land in the water and it will tell you something about an explosion. The pellets all get further and further away from each other as they travel. So increasing distance between entities doesn't prove expansion.
You haven't been paying attention to what you've been told then. We've explained more than once how expansion works and it does not work like an explosion. I've given you specific reasons why in several of my posts. Read the posts in the thread. Read the links. Re-read the posts. Re-read the links. Ask specific questions about things you don't understand in the links and the posts. Stop suggesting that an explosion can explain everything, because it cannot. Even if you don't understand why it doesn't work, trust us when we say that it does not. Help us help you.
 
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The more distant they are, the faster they are receding, so it amounts to the same thing.
This is as far as I know based on irreffutable evidence rather than a theory.
Yes. That much I know. And it doesn't tell me whether we're talking about expansion or explosion.

Here is a fact for you. I've mentioned a couple of times the results of a shotgun blast over still water. Here are the facts from my own experience and observation: Of course the flat, still water is needed so that the results can be readily seen. But if you aim a shotgun just a very few degrees above horizontal and shoot, the first pellets to hit the water will be the very fast ones that land farthest away. Then the remainder fall in behind it as much as twenty feet short of the first, and the closest one hits the water last. That's an explosion, and that much at least reflects what you said about the universe.

If one of the pellets in the more middle area of the pattern were the earth or if you could stand on it as it is fired and watch the other pellets, they would all be moving away from you. The pattern proves it.

From my reading that I've been doing since I first posted here, the question has been partially resolved. I now know that there is a theory that says there are two components: expanding space and moving galaxies, and this contributes two components to the redshift -that due to planets moving as a consequence of expansion, and that due to planets moving as a consequence of inertia. So the question is now just whether there really is expansion of space going on at all. It would be nice if it were because it would seem to open up future technological possibilities that would take advantage of it for travel.

It's a theoretical model, but it has one big advantage over an "explosion" theoretical model: it explains our observed data. So it isn't a "mere" theory; it's a theory that has observational support.
Ok. Good. That's worth noting. Thanks. Now would you list for me the specific observed data that an explosion does not explain? Please keep in mind my previous rejection of certain "observed data" that can be explained by an explosion.

You haven't been paying attention to what you've been told then. We've explained more than once how expansion works and it does not work like an explosion.
Pardon me but I have been paying attention. I understand the difference now. I just want to know how reliable the evidence is for expansion and whether there really is any. So far I think what you have presented that you say cannot be explained by an explosion, turns out that it can be so explained. The shotgun analogy seems to me to explain the "explosion" component/explanation quite well without resorting to ideas of expansion.

Stop suggesting that an explosion can explain everything, because it cannot.
What does it not explain?

Even if you don't understand why it doesn't work, trust us when we say that it does not.
You are asking me to accept what you say on faith just because you said it. Sorry but no. I came here for fact-based, evidence-based information. You have provided some and I think you all for that.
 
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We are told that within the event horizon of a black hole, physics fails.
I found this thread already in progress so I missed this on a first read-through. This is not correct; physics works just fine inside a black hole's horizon. Who told you it didn't?

What about the Doppler component?
In a non-stationary spacetime, there is no such thing as a "Doppler component" as distinct from something else. There is just redshift. The reason we can separate out a "Doppler component" in SR is that in flat spacetime there is an invariant meaning to "relative velocity" for objects that are spatially distant from one another. In a general curved spacetime, there isn't; "relative velocity" only has meaning locally, where "locally" here means "on time and distance scales much smaller than the scale of the universe's expansion". So, for example, it's meaningful to say that we in the solar system are moving at a few hundred km/sec towards the constellation Orion (or whatever it is, I may not be remembering correctly); but it's not really meaningful to say that a galaxy a few billion light-years away is moving away from us at 50,000 km/sec. When you see numbers like that quoted, they are converting the observed redshift to a recession velocity using the Doppler formula, but the "recession velocity" defined in this way is not a "relative velocity" in the SR sense, because it can be faster than light (and in fact it will be for redshifts greater than 1). It's just an expression of the rate of change of comoving space coordinate with comoving time in convenient units.

Now would you list for me the specific observed data that an explosion does not explain?
Multiple posts in this thread have already done that.

Please keep in mind my previous rejection of certain "observed data" that can be explained by an explosion.
I don't think you have established that; I think you have just waved your hands and said it looks to you like observed data can be explained by an explosion, and then stopped there. What you should be doing is trying to understand the actual mathematical model underlying the ordinary language phrase "expanding universe". Some good places to start are here and here. Then, if you want, you could compare this with a mathematical model of an ordinary explosion, to see where their predictions for observed data differ. Then you could look at the actual data to see which one is right.
 
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increasing distance between entities doesn't prove expansion.
This is an example of what I called "waving your hands" in my previous post. Cosmologists are not just saying "increasing distance proves expansion". We have a detailed model of exactly how redshifts should vary with other observables (such as brightness of objects, angular size of objects, etc.--the Ned Wright cosmology tutorial I linked to goes into all this), and we compare the model with how redshifts actually do vary with other observables, and it fits. An "explosion" model would predict very different relationships between these observables.

the article said that the redshifts of galaxies include both a component related to recessional velocity from expansion of the Universe, and a component related to "peculiar motion" (Doppler shift).
Can you give a reference? Is it a pop science article or an actual scientific paper? Pop science articles say all sorts of things.

For what it's worth, however, in the standard cosmological model, there is a set of "reference" objects, called "comoving" objects, which have constant spatial coordinates in the standard FRW coordinate chart. An actual observed object, like a galaxy, will probably not be exactly "comoving", so for purposes of calculation in the model the object's "peculiar motion" is defined as its motion relative to a "comoving" object at the same spatial location. The calculated redshift in the model thus has two parts: the part that is calculated for "comoving" objects, and the part that corrects the calculation to account for the fact that the observed object is not exactly "comoving". But that's purely for conceptual and calculational convenience. Nothing we actually observe tells us the peculiar motion of objects at cosmological distances; all we observe is redshifts vs. other observables, and the output of the model calculations is an expected distribution of redshifts vs. other observables assuming that peculiar motions have some reasonable average distribution.
 
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I found this thread already in progress so I missed this on a first read-through. This is not correct; physics works just fine inside a black hole's horizon. Who told you it didn't?
I don't recall "who told me". Ok. So physics works just fine inside a black hole horizon. The "singularity" is within a black hole horizon. So does physics work in the case of a singularity? Apparently you are saying "yes".

In a non-stationary spacetime, there is no such thing as a "Doppler component" as distinct from something else. There is just redshift.
What we have is planets and galaxies all at distances from each other. My understanding is that with regard to galaxies, we have them all moving away from each other due to motion and inertia, and we have them moving away from each other due to expansion of spacetime. I understand you to be saying that there is no redshift due to movement other than that of expansion of spacetime. But various sources that I've recently read said there are two components to redshift and they are as I mentioned. To be clear, are you saying those sources are incorrect?

But unless I am very confused by now, it looks like participants on this forum claim or seem to be informed and knowledgeable, yet they disagree on these things and a few others. That aside, this discussion of redshift now leaves me with no solid possibility of redshift in any way being evidence for expansion rather than explosion. Maybe another aspect of this will provide such evidence. Let us proceed and find out. Maybe it would be the speed at which distant galaxies are receding from us. Is it a fact that the redshift alone in such cases definitely, unquestionably indicates a speed greater than that of light?

Multiple posts in this thread have already done that.
And I think I showed (to my satisfaction) that each one is explainable as features of an explosion, including the observation of all galaxies moving away from us.

I don't think you have established that; I think you have just waved your hands and said it looks to you like observed data can be explained by an explosion, and then stopped there. What you should be doing is trying to understand the actual mathematical model underlying the ordinary language phrase "expanding universe". Some good places to start are here and here.
Thanks. I will look into that. But I am not trying to prove anything to you folks. Given my understandings combined with things you have all said on the subject, I find my original question unanswered to my satisfaction. But I will take a break here to look into those two links you just provided. Thanks.
 

Drakkith

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And I think I showed (to my satisfaction) that each one is explainable as features of an explosion, including the observation of all galaxies moving away from us.
PF doesn't exist to convince people that science is right, it exists to teach people who want to learn. You obviously don't care that much about learning, despite your claims. Thread locked.
 

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