Conceptualising - Assistance Sought
Hi folks. If anyone can help with the following i'd be grateful:
i'm having trouble getting my head around a few concepts, which i feel should be conceptualizable (that's gotta be a word!). I'll buy you a beer on Wednesday if you can relieve me of my ignorance!

Firstly, if space is expanding, and the space between everything is getting larger, then this includes the space between atomic and subatomic particles. If this expansion is isotropic (is it?), then we are getting bigger as the stars around us (and their distance from us) are too. In such an expanding world, there is no reference, so how do we know the universe is expanding (an expanding universe would seem constant to an equally expanding person)? or are parts of it expanding faster than other parts? or is there something logarithmic going on here?
Or perhaps I've misinterpreted this, and its is not space that is expanding but only things are moving away from each other IN space - but this would require a sort of antigravity force that everything exerts on each other. (ok, so i'm playing with ideas here to exemplify my problem of conceptualisation).

It wouldn't be so tough a conceptualisation if there was a more dense centre form which things were expanding, but there is no centre (unlike how a sound wave explosion might travel through air in all directions from a central vibrating point). We can conceptualise an initial singularity though. And after inflation everything expanded away from everything else in an accelerated way…. but no centre. I think this is the idea - but if we can't conceptualise it, what sort of idea is this? Can a concept be inconceivable (apart from inconceivability itself of course)?

And there is no boundary to our universe system - Like Hubble, we can conceptually shrink all stars separation distance backward in time to a point, but surely then looking "out" from the "outer" we would see no other stars. Apparently not - there is no outer boundary. (Even though other universes may potentially collide with our own in some multiverse theories).

In short, how can we conceptualise an expanding universe? what does it even mean to expand all at the same time with no starting point as a reference? The usual 2D modelling of dots on the surface of a balloon is useful. And i can transpose that in my head to "see" the concept in 3D, where the space between all stars/galaxies/galaxy clusters increases over time - well kinda…. i can if i take a point within this system and assume that only the space between stars expands and that i (and the stars around me) don't expand. Then when i conceptualise contracting this system i cannot step outside of it because there is no outside, so i visualise contracting to a point of maximum density where everything is touching. I cannot go further (its still gigantuan and not in any way spherical or even blob-like in nature!) because to permit this conceptualisation i had to disallow movement within matter (remember my initial conditions, to avoid everything expanding without any reference, required that the stars and i got more dense relative to the expanding universe).

Does it even make sense to posit that we might conceptualise our universe from the outside which a Big Bang concept seems to necessitate? If we cannot conceptualise this, what does it mean to have a concept of a Big Bang?

The cosmic background microwave maps that we were shown in last two lectures are conceptual spheres - I asked about what they represented conceptually and Dayal spoke of envisaging cigar smoke in a darkened room where we could not see the walls. I like this analogy (and i love the smell of cigars!) but I still feel conceptually ignorant - apparently the universe is not expanding into a void.

I feel as though either it is possible to conceive of this expansion (please help me!), or if not, we have an issue: the thinking that produces this inconceivability arose from the domain of the conceivable - foundations from a conceivable world have been extrapolated into the absurdly abstract yet we can still speak of these notions. I can see that abstract mathematics might be useful for predictions or relations between things, but what does it mean to believe mathematical extension that is not demonstrable and science that explains by pointing out the inconceivable?

How is this leagues apart from the leap of faith that religions make at the end of their sequence of logic? To posit that the Big Bang is a special case to which no analogy can be drawn, arrives at a similar loss of convincing traction that the Christian argument arrives at when they posit that god is the singular and incomparable uncaused cause (granted science provides more evidence, but the absence of comparison is similar).



Secondly, in a vacuum such as what Dayal was describing today, if there is no matter, can there be time? If there is no matter then there is no change. A world in which there is time but no change seems to be indistinguishable from a world in which there is no time and no change. What does it mean to add time to a unchanging system?

Surely i've just missed a few key points here so help is appreciated. I apologise in advance to lecturers if i've simply forgotten/misinterpreted stuff mentioned in lectures, but hey, at least i'm owning up to what i don't understand.

Senan.




an expanding universe would seem constant to an equally expanding person

No, because the speed of light stays constant. The speed of light is not affected by the expansion.

We don't measure cosmological distances, e.g. between stars, by layout out our bodies along the line between them. If we did, you're right, at least to a first approximation — they'd appear not to change. We use light, which moves at a constant speed and therefore is slowing down relative to the distances between stars (which means the red shift behaves as you'd expect, regardless of whether our bodies are expanding).

The reason I said "at least to a first approximation" just now is that the molecules in our body are pulled together by electric forces MUCH more strongly than stars pull each other together. So in fact, for that rather mundane reason, the stars would appear to be expanding even if we did use our bodies to measure them. But I think the speed of light reason is more relevant, since it's more fundamental to the theory of relativity, and also since that's what we actually use for distance measurements.

Secondly, there is matter in a vacuum on most current theories. As for what would happen to time if there wasn't any matter in a vacuum, you can please yourself, but if you say there's no time in that case you'll have a much more complicated physics. It's not by accident that we started the course with the idea that simplicity is important in physics. It would work either way, though, so if you prefer that then go for it. I don't think it raises any deep issues either way, because this is just boring old physical time, which we can theorise however we want. If we were talking about perceived time, things would be more awkward, because we'd be constrained by the facs of how we actually perceive time ... but that's not going to be a problem in a vacuum!

Jason


-


Ok! Thanks Jason for recovering my oversight regarding the reference point of space expansion - which is of course the constant speed of light. How elegant! The proposition that space is expanding that is, not you, but I still owe you a beer!

And thanks for reminding re time in a vacuum – you have mentioned this before, but I guess learning requires reminding from time to time. I will however admit that I find it difficult to separate the notions of duration/perceived time and “just boring old physical time” that presumably is a measure of change without perception.

However, I’m still at a loss for how I might visualize a non-centred, non-spherical universe that exploded from a singularity.

This is also interesting: (thanks to my dear friend Mark Clemmens who alerted me to this)

http://onswipe.com/thedailygalaxy/#!/entry/the-universe-is-not-expanding-a-radical-alternative-to-big,537d03f6025312186c0ae7db

This article refers to a yet-to-be-published paper that suggests alternative ways of interpreting redshift and thus posits that the universe may not be expanding.

Maybe we shouldn’t get too comfortable with our Big Bang model, but perhaps more importantly (well for me at least) the article highlights the value of scientific models and the nature of science:

“Wetterich says that his interpretation could be useful for thinking about different cosmological models, in the same way that physicists use different interpretations of quantum mechanics that are all mathematically consistent. In particular, Wetterich says, the lack of a Big Bang singularity is a major advantage.”

In standard Big Bang cosmology, we observe data, theorize that space is expanding, and then extrapolate this backwards in time to arrive at a singularity. Little wonder Fred Hoyle referred to it tongue-in-cheek as the “Big Bang” – a singularity presents many conceptual problems. My reading of the quote above is that Wetterich is not only questioning the value of alternative understandings of redshift data, but reminding us that science may be recognizing limits to what it can know and perhaps suggesting that to have more than one theory (such as in quantum mechanics) is an acceptable conclusion.

A multi-conceptual truth for science to rest upon? Could this be the next scientific revolution? – it does seem to violate the one-truth finding purpose of science. And it doesn’t look good for those not inclined towards phenomenalism. Yet perhaps a pluralistic view of the world is not so bad. Might we remain at the sort of wonder that skeptics have reminded us of all along? Perhaps we need science to predict more than we need it to explain – we could conceivably utilize models as a “it could be this way” approach, and accept that our ability to extract further data or comprehend more deeply has its limits.

The Big Bang idea (as discussed in the thread above) seems to be an example of where science can predict but fails to really explain. Just because an evidenced theory can predict does not mean it is correct or necessarily explains something well. I feel that some of the problem here arises from moving beyond the conceptually analogous understandings (as stated in the thread above). We conceive of things and understand them in reference to some metaphor of what we have previously perceived. So it is possible to conceptually visualize expanding space in 3D because we have experienced a balloon surface expanding and can extrapolate that in all directions. We might even say that we can “see” points in our “mind’s eye” moving away from each other like raisins in an expanding loaf, and even move around that “expanding space” as a point of consciousness, examining what it “feels” like. Yet when we deflate our raisin cake it comes back to a central position. And it seems this is the best we can do with computer graphic depictions too.

The reversal of time back to a non-central “singularity” such as Hubble’s Law entices, provides a model for understanding. This model points to the universe expanding from the size of a walnut, but with no centre or boundary! The concept appears to be an odd collage of the conceivable (expansion/contraction of space) with the inconceivable (a centre-less and boundary-less beginning). Our visual concept of a big bang requires that we have a central focus and a spherical-like boundary rolling out into a void, (unless someone can convince me of visualizing it otherwise – btw the beer wager stands!). As this is not an actuality (there is no centre or sphere boundary), I feel the best resolve is to see this merely as a model, (not a actuality we can envisage), as Wetterich seems to infer.

However it is unclear whether a strict adherent of science is allowed this flexibility as a conclusion. How much of this Big Bang idea is model and how much supposed truth? Can we really hope to prove the existence of something we cannot conceptualize? And if so can we really glean some satisfaction form this explanation?

The generally promoted proposition is that space expands, and time as we know it and laws of nature as we know them suddenly popped into existence. That’s absurd! It may be true, but it’s still absurd. It’s absurd because we have nothing like that to which we can relate. It is debatable whether infinite existence is more profound than the Big Bang idea, but neither really explain, because explaining requires relating things to what we have previously experienced. Do you agree?

In short, I am suggesting that our scientific process of arriving at “fact” is not only bound by physical limits (such as the speed of light in an expanding universe), we are also bound by our experiential cognition, which leads to our comprehension. To go beyond that (eg. mathematically) is to move into a world of models that will likely always have competing models.

My argument is this: no matter how much evidence we might accrue for a theory, it does not explain much unless we can make cognitive and perceptual sense of what it suggests. If something is incomparable to anything else, asserting its existence is tantamount to mere belief. Science differs from belief structures in that it will vary its prepositions according to evidence and mathematics. But if what science offers is something to which we cannot relate, how much progress towards a convincing explanation has really been made? Those of us whose minds are incapable of abstract conceptualization are certainly relegated to merely believing those who supposedly can.

Senan.




Yes, I agree. And in fact both Dayal and I have said that in lectures. :-) The singularity is something you get in General Relativity, but all it means is that the theory breaks down at that point, not that a singularity is something that actually happens.

My browser won't show me the link you posted, which is a pity. I'm all in favour of space not expanding if that's possible.

Jason