How Do Scientists Know It's Space Expanding Not Galaxies Moving?

[Rhondazvous]

I understand about the rubber band/raisin bread dough analogies. My question is what made scientists look at the universe and say hey, you know what, the galaxies aren't moving. Space is expanding. What tipped them off to make this distinction?

[Gawdzilla Sama]

I'll take shot: Space is defined by the matter in it. Outside of space is nothing. (Consider a vacuum. Then take away the vacuum and consider what's left.) So we see all galaxies moving away from each other. The matter that goes with them are creating what we call "space".

And remember, this is astrophysics, so "getting it" may not be all that easy.

[chimp3]

I am reading a book by Neil DeGrasse Tyson right now and he explains this. Space is expanding because some galaxies are moving away from us faster than the speed of light. Since matter can not go that fast it is the expansion of space.

[Gawdzilla Sama]

I am reading a book by Neil DeGrasse Tyson right now and he explains this. Space is expanding because some galaxies are moving away from us faster than the speed of light. Since matter can not go that fast it is the expansion of space.

Yep, and the balloon analogy Rhondavous mentioned is a great example of "This is space, this isn't." We're inside the balloon. There's nothing outside it. In this Universe, at least.

[Brian37]

I understand about the rubber band/raisin bread dough analogies. My question is what made scientists look at the universe and say hey, you know what, the galaxies aren't moving. Space is expanding. What tipped them off to make this distinction?

It is really not that hard to understand, it is not that different than knowing your car speed can be measured by time and distance. 

Maybe this will help. And others can correct me if my analogy is wrong, but the way I understand it expansion can be explained more like inflating a balloon with a fast air tank, if you have ever seen that. 

A easy book for laypeople, and I am currently reading it, and yes, it will blow your mind, Neil Degrasse Tyson, "Astrophysics, For People In a Hurry".

Lets just say expansion is "FUCKING FAST".

But here is a wiki article on space expansion. 

https://en.wikipedia.org/wiki/Inflation_(cosmology)

[Edwardo Piet]

Is there a difference?

I don't believe science can detect reality... only our experience/own models of reality. So IMO what is expanding is the parts that we can detect and do equations about. I think that the full reality behind it is infinite. I think the universe is eternal and energy changes but it's eternal and can't come out of nowhere. No I don't think this means god whatsoever. I think it's simple logic that every thing has always existed and nothing can come from nothing, ultimately speaking. The creations who use that argument to say "therefore God" are simply retards... the basic logic does actually make sense.

We, live in the world of phenomena and that is the world science tests. Our instruments are less limited than us but they are still phenomenological and limited... we still need to use our senses to use those instruments/tools. And yes there is also the theoretical mathematical side of science... but it has to be based on the empirical side. We don't pull information out of nowhere. It's logically impossible for science to ever test anything besides how we experience reality.

Sure you may say "But what about how we can figure out how bats, for example, see the world very differently to us."

Well, sure, but we still have to use our own senses and instruments to figure that out. And we have to see it from SOME perspective. We're still ultimately studying the EXPERIENCE of reality and not reality itself. Science can't test what the universe would be like if we weren't here to observe it. We can test what existed when the universe began... BUT THAT'S STILL US TESTING OUR OWN EXPERIENCE OF THE EVIDENCE LEFT BEHIND. What it is in reality outside of our experience and it's limits and the tools and theories behind it... may be quite different.

TL;DR: It's semantics. The evidence indictates that scientists experience clues and proofs of universal expansion that has gone on since the beginning.... but that's still studying their own experience of that evidence, ultimately, and BEHIND all that evidence, that is indeed correct, there may be a deeper reality that is by definition impossible to ever experience or have evidence of.

Fully truly objective reality is the noumenological world, the world of noumena as opposed to phenomena. And it's by definition "Whatever exists beyond experience" so by definition science can never have evidence of it.

I think in 'real' reality the unviverse is very much like the philosopher Paramedies thought it was:

The traditional interpretation of Parmenides' work is that he argued that the every-day perception of reality of the physical world (as described in doxa) is mistaken, and that the reality of the world is 'One Being' (as described in aletheia): an unchanging, ungenerated, indestructible whole. Under the Way of Opinion, Parmenides set out a contrasting but more conventional view of the world, thereby becoming an early exponent of the duality of appearance and reality. For him and his pupils, the phenomena of movement and change are simply appearances of a changeless, eternal reality. This interpretation could settle because of various wrong translations of the fragments. For example, it is not at all clear that Parmenides refuted that which we call perception. The verb noein, used frequently by Parmenides, could better be translated as 'to be aware of' than as 'to think'. Furthermore, it is hard to believe that 'being' is only within our heads, according to Parmenides.

Of course by 'real' reality I mean ultimately 100% objective reality that can never be experienced or perceived by any living being at all. It's merely a conclusion that can be reached through logic.

That's what I mean by 'real' reality because.... many people wouldn't call it 'real' if they can never ever experience it. It hardly applies to their life, or their reality, so it's certainly not practical reality. 'existence' is probably a better word. Existence without experience.

Einstein agreed, I reckon:

Einstein himself thought so. He believed that there must exist hidden aspects of reality, not yet recognized within the conventional formulation of quantum theory, which would restore Einstein Sanity. In this view it is not so much that God does not play dice, but that the game he’s playing does not differ fundamentally from classical dice. It appears random, but that’s only because of our ignorance of certain “hidden variables.” Roughly: “God plays dice, but he’s rigged the game.”

source:

https://www.scientificamerican.com/artic...-insanity/

Of course God didn't believe in an actual God. The "God" he spoke of was merely a metaphor for his belief that the universe made sense.

[Alex K]

When space expands, redshift is the sum of all expansion during the light travel. When Galaxies move, the redshift from the Doppler effect is the difference between movement speeds at the time of sending and receiving. Big difference.

[Anomalocaris]

When space expands, redshift is the sum of all expansion during the light travel. When Galaxies move, the redshift is the difference between movement speeds at the time of sending and receiving. Big difference.

The question is how does the observer tell the difference?

If I am not mistaken, there is no way to tell the difference in the causes of redshift through single direct observation.  

The difference has to be inferred from patterns seen over a large body of observations, which shows galaxies  exhibit a particular pattern of red shift highly correlated to their distance, as calculated by comparing the observed brightness of phenomenons believed to have narrow range of intrinsic brightness.

If the pattern of red shift comes from galaxies moving, there needs to be an explanation for how galaxies come to move in relative terms in this extremely regular manner.   There is none so far that fits the data and is relatively free from large number of ad hoc assumptions.  

I believe it so happens that the universe expanding rather than galaxies moving fits the pattern of data far better while requiring far fewer addition as hoc assumptions.

[Alex K]

You're right, from one observation of a redshift and nothing else you can't deduce much. But there is the relationship between brightness and redshift which is difficult to explain, and also all the effects that go into the correct prediction of the Cosmic Microwave background such as the Sachs Wolfe effect make no sense if space doesn't expand.

[Edwardo Piet]

So... logical deductions...

...BASED ON experience.