Space is flat?

geordief

I am predisposed to believe that I would almost certainly be asking for the "cause of the cause" (otherwise I would be a believer in a God -which I am not)

And I don't mind outlandish causes if they fill the gap.

But I didn't ask for a theory of gravity -just ,in particular why an object with mass should distort spacetime (aside from a mathematical explanation).

Or is that the be all and end all of gravity-objects with mass distort SpaceTime and no further questions on the subject are relevant? (I don't mean to come across as indignant!)

Are you saying that my question "what in particular causes an object with mass to distort SpaceTime?" is a nonsensical question with the only possible answer "because it does" or "because that is what gravity is"

d3mm

Cyghost

My question is about the overall shape of observable universe, not what happens locally in the vicinity of a large mass. I am asking which of the three theories you mention, do you believe is the most appropriate after new evidence such as WMAP and the accelerating expansion of the universe.

bapowell

Yes, I'm aware that multiple theories can offer competing explanations for a given data set. The reason that I misunderstood what you wrote is because you were not being clear. You state that "The WMAP can show what ever it wants, but how one interprets the mathematics, it is still just another theory ready to dispute." How one interprets the mathematics? I guess you mean -- how one uses mathematics to explain the data. OK, got it. But it's still not "just another theory to dispute." There is an entire program for comparing the merits of competing theories given data, and yes, this program needs to be exercised in the face of any scientific data. The argument you seem to be advancing is not specific to the CMB -- it can apparently be applied to any body of data. It is simply impossible to use induction to obtain a uniquely correct theory. So, I am interested in knowing how your argument differs from that made by Hume et al. hundreds of years ago regarding the problem of induction.

If you want to debate the merits of competing explanations for the CMB, then fine. If you are just pointing out the obvious limitations of all experimental science, then I think you are taking this thread way off topic.

His question has to do with the fact that if space is flat (in the sense that R, the curvature scalar, is zero), how is it that space-time is curved? It has to do with the fact that the spatial metric components, [itex]a(t)x^i[/itex], while indeed giving flat hypersurfaces, are function of time. In this case, the curvature scalar is non-zero,
[tex]R \propto \frac{\ddot{a}}{a} + \left(\frac{\dot{a}}{a}\right)^2[/tex].

Do you still not agree?

Cyghost

I'd probably trust the astrophysicists on this and would say model of the universe that is “flat and infinite" (although I use the term infinite loosely as the visible region of space) it seems to match the results pretty closely.

There is always the possibility of some form of galactic foreground contamination also the long delays in releasing the results was confusing, or if data was incorrectly inserted such as if the wrong spectral index is used to convert the difference between power spectra at different frequencies into a point-source contribution, then there will be a systematic error in the cosmological parameters.

clamtrox

Okay, let me rephrase my answer more clearly: This question is not answerable using general relativity. That theory has nothing to say about the mechanism. If you want to invent something, like the butterflies I mentioned in the previous post, then if that satisfies you, fine. It would be even better if you could come up with a mechanism which has some observable effect on physics, like small deviations in the gravitation field around massive bodies or in the path of photons, or whatever. If the mechanism has observable consequences, then you can make experiments and decide whether it's true or not. If it's something you've invented to keep you sleeping at night (like the many worlds interpretation of quantum mechanics), that's possible too.

Let me give you another example. In quantum electrodynamics, you describe the interaction between electrons and photons. The theory is extremely successful and accurate - it can predict basically everything you can see, and more. However, an inquisitive soul like yourself might ask: what's the mechanism through which the photons and electrons interact? And to that question the theory has no way to answer; they simply do.

Cyghost

Ok I may have been a little ambiguous with my statement regarding the WMAP.

No :)

bapowell

OK. What exactly do you disagree with?

EDIT: Or, "No", you agree?

PhyPsy

The recent WMAP data has narrowed the range of possible curvatures of the universe, but unfortunately, it still leaves open the possibilities of a universe with positive or negative curvature. I suppose you could say it makes the possibility of a flat universe more likely, but if the universe truly is flat, will any measurements ever make us 100% sure of its flatness? It seems like we're just doomed to continue narrowing the range of possible curvatures further and further without really putting the nail on a curvature of 0.

Cyghost

"No" I agree this time.
Space is Flat (By flat I mean parallel and no intersecting lines) - Space-time is curved

Just a quick question : "Probably off topic again"
If space time is curved, then even the most minimal curvature would eventually produce a circle. Does that suggest space-time is circular?

Interesting relative quote:
"I hold that space cannot be curved, for the simple reason that it can have no properties. Of properties, we can only speak when dealing with matter filling the space. To say that in the presence of large bodies space becomes curved, is equivalent to stating that something can act upon nothing. I, for one, refuse to subscribe to such a view" -- Nikola Tesla

bapowell

Yes, very true. Even with extremely precise future measurements, there will always be some margin of error about true flatness. There are people who make statistical arguments about the geometry of the universe using Bayesian model selection: http://arxiv.org/abs/arXiv:0901.3354. The idea is that the flat universe model is simpler and more predictive than one with curvature, in the sense that one with curvature requires an additional tunable parameter. If the data disfavors the added extravagance of extra parameters, the associated model is considered less likely.

Of course, this is a statistical argument that is best applied to statistical models. I like to think that our theories of the universe are more than mere statistical models, that they say something about physical reality. In this sense, I am personally not sure how to interpret studies that use Bayesian model comparison as a means of interpreting physics.

Cyghost

As I mentioned I do tend to sway to the current flat universe hypothesis from the WMAP survey but what I was trying to say previously is, and although it is again off topic I feel I should explain myself, that although the data matches a flat-infinite universe to an approximate but fairly accurate calculation, that doesn't mean I am 100% convinced that it is the only concrete hypothesis as suggested. We cannot see past the CMBR and can only speculate as to what is beyond.

As an example say the universe contained a extremely minute curvature from both negative to positive degrees such as in a ripple of a wave form and they were precisely equal so when you make your calculations regarding wave dynamics it also produces a close match for WMAP survey data and appears flat. If you measure curvature from one end to the opposite the resulting curvature equals zero as both equal negative and positive curvature cancel each other out.

Another Example:
If you imagine a pool of water and you drop a stone in the centre and observe the rippling wave forms that emanate from the centre you will see the ripples spread further and further apart and the resulting the area within each wave peak increases with time including the distance between each peak of the wave form with similar basic characteristics of expanding universe.
Even if you were located close to the peak of one of the ripples you could never see past or over the adjacent ripples as they are basically a similar height and as the opposite side of the peak must have a negative curvature and the areas beyond the peaks would not be visible within your entire viewing area so essentially from peak to peak is the only observable area, although beyond that observable area more ripple do exist. So speculating if our observable universe exists within the area between two wave peaks of a rippling universe it would be safe to say would could not view past the CMBR and the resulting curvature would appear zero as from one peak to the next it must contain equal positive and negative curvatures as the curvature reverses at the point of the trough of the waveform.
It is basically the same flat surface that was original present before the event (Dropping the stone) but now with a more fluid constitution but as the wavelength of the ripples gets longer and longer, the effects eventually disappear completely and the ripples would have no effect on the observable universe and would appear as a flat universe and that nothing had previously existed beyond CMBR, but it doesn't confirm that the universe was always flat and infinite.
So for me just saying ok well we have survey data so that is the final answer is not fulfilling all possibilities.
This is just a couple of examples of how the WMAP survey data may be misinterpreted and I don't claim to fully comprehend the advanced physics involved of the data conversion but just offering the thought that the universe and our understanding of it is an evolving process and we should be open to alternate possibilities.