There are assumptions in every field of study and they need to be continually tested. Two of the main assumptions behind modern cosmology are homogeneity and isotropy on the appropriate levels of scale. These assumptions are constantly being challenged and tested. Currently the Wilkinson survey of the CBR measures these in excruciating detail. The influx of data is the source of excitement. First we discovered so much homogeneity in the background radiation it was difficult to explain. One explanation and perhaps the most popular is the ad hoc hypothesis of an inflationary field. But whether you buy into inflation or not, the assumption of homogeneity is no longer an assumption. It’s a measurable property of the OBSERVABLE universe.Quote:
Too many assumptions.
Other assumptions are the applicability of general relativity (GR), thermodynamics, chemistry etc. These too are constantly being challenged and tested.
Exciting and true. Cosmological theories can only apply to the observable universe. There’s a lot of speculation on what was on the other side of the singularity, on bubble universes etc. So far I agree, if it’s not about the observable universe it’s speculation. This point of agreement reminds me of two interesting sorts of situations that can arise in science.Quote:
We have no idea how big the universe is, or even if it has such a limitation at all.
1) There are assumptions which cannot be directly tested which if true would have observable consequences. (This was originally the case with the atomic theory of matter).
2) There can be directly testable hypothesis which if true outside their testable range have consequences outside their range as well. This is the case with bubble universes.
Anything the falls into category two is in danger of remaining speculative unless the range of what is observable sufficiently expands.
This last quote illustrates a point on which it’s very easy to become confused. Every galaxy cluster is moving away from every other cluster. The distances between each pair is increasing with time. One doesn’t have to have an absolute determination of location to establish this, our locations relative to each other measured at different times would, for example, establish this. We also know the rate of the expansion. The rate at which two clusters recede from each other depend on the distance between them and is equal to about 50 km/s per megaparsec.Quote:
There's this assumption floating around that Hubble's claim of discovery of the red shift proves expansion. Relative to what? We're moving, & we really don't know how fast or even in which direction relative to everything else.
In the context of the big bang theory the clusters do not move away from each other through space but with space. Everyone has heard of the paper dots pasted onto the surface of an expanding balloon analogy. This part of the Big Bang can’t be directly tested but it’s consequences can. Moreover the underlying theory of spacetime required for this conception (general relativity) can and has been tested.
It takes a bit of nerve to tackle some questions, that I will grant. And I agree that human knowledge is on the puny side. But let me repeat. The big bang theory doesn’t claim to know the beginning of the universe. The theory has a big hole at the beginning (otherwise known as the big bang singularity). Formally, the big bang theory is mute about the beginning of the cosmos and it’s reason to be. But it is a successful, testable theory of the observable universe which has so far survived all tests.Quote:
I think it's egotistical to say that any of us puny humans have the answers to questions of beginnings & endings.
Personally, I don’t understand how accounts of the early universe, or accounts of the evolution of life on Earth, or the accounts of the beginning of solar system etc. threaten in anyway religious or metaphysical belief. Religion and metaphysics aren’t in the business of finding universal physical laws, nor the business of explaining the relation of one phyla to another.
True enough. But that doesn’t discredit ALL the answers. A good answer is just a seed from which springs more questions.Quote:
Sorry. There's just too many people claiming to have answers. Every time I hear one, I have more questions.
By the way, hippiefried, you’re an awesome contributor to this forum. I just wanted to thank you for all your insights and opinions. Even the ones with which I disagree.
