surreptitious57 wrote:If dark energy did not exist then why would the Universe still be expanding ?
Just from the initial expansion. We knew from observation that it was still expanding from Hubble's work in the 20s and 30s, and there was no reason to suppose that it wouldn't be, although it was expected to be slowing down due to gravitational attraction of all the matter and dark matter (dark matter was postulated not long after the Hubble observations based on the orbits of stars in the outer edges of galaxies, especially small galaxies). When it was observed in 1998 that expansion was accelerating, the research that revealed it was actually geared to finding out how much expansion was slowing. I remember the announcement like it was yesterday. I was gobsmacked.
How is it possible to accurately measure its mass when it is not static ?
Some of it is extrapolation from such things as overall energy density, which is isotropic and homogeneous as far as can be ascertained. That it isn't static isn't actually relevant.
One could measure the distance of the furthest star by how long it tales light to reach Earth but expansion means that that figure would not be accurate beyond the time of measurement
It doesn't matter, not least because we can measure red shift, which is also a measure of distance on the largest scale, due to Hubble's law.
I know you've seen the Krauss lecture, so you'll remember the diagram with the square of dots showing how expansion is the same in all directions, regardless of where you are. Another feature of that is that it shows how there is a direct relationship between how far away something is and how quickly it's receding from us. What this means is that we can measure how fast something is receding and directly assess how far away it is by its rate of recession.
Where did the energy that caused the quantum leap of the Big Bang originally come from ?
It didn't have to come from anywhere if there is no energy. Either way, it's the wrong kind of question. Since this has come up, and since I've been meaning for a while to type this up and add it to my clippings library, here's Brian Greene:
Brian Greene wrote:Quantum mechanics is a conceptual framework for understanding the microscopic properties of the universe. And just as special relativity and general relativity require dramatic changes in our worldview when things are moving very quickly or when they are very massive, quantum mechanics reveals that the universe has equally if not more startling properties when examined on atomic and subatomic distance scales. In 1965, Richard Feynman, one of the greatest practitioners of quantum mechanics, wrote:
"There was a time when the papers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when one man did because he was the only guy that caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in one way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics"
Although Feynman expressed this view more than three decades ago, it applies equally well today. What he meant is that although the special and general theories of relativity require a drastic revision of previous ways of seeing the world, when one fully accepts the basic principles underlying them, the new and unfamiliar implications for space and time follow directly from careful logical reasoning. If you ponder the descriptions of Einstein's work in the preceding two chapters with adequate intensity, you will - if even for just a moment - recognize the inevitability of the conclusions we have drawn. Quantum mechanics is different. By 1928 or so, many of the mathematical formulas and rules of quantum mechanics has been put in place and, ever since, it has been used to make the most precise and successful numerical predictions in the history of science. But in a real sense those who use quantum mechanics find themselves following rules and formulas laid down by the "founding fathers" of the theory - calculational procedures that are straightforward to carry out - without any real understanding why the procedures work or what they really mean. Unlike relativity, few if any people ever grasp quantum mechanics at a "soulful" level.
What are we to make of this? Does it mean that on a microscopic level the universe operates in ways so obscure and unfamiliar that the human mind, evolved over eons to cope with phenomena on familiar everyday scales, is unable to fully grasp "what really goes on"? Or, might it be that through historical accident physicists have constructed an extremely awkward formulation of quantum mechanics that, although quantitatively successful, obfuscates the true nature of reality? No one knows. Maybe some time in the future some clever person will see clear to a new formulation that will fully reveal the "whys" and the "whats" of quantum mechanics. And then again, maybe not. The only thing we know with certainty is that quantum mechanics absolutely and unequivocally shows us that a number of basic concepts essential to our understanding of the familiar everyday world fail to have any meaning when our focus narrows to the microscopic realm. As a result, we must significantly modify both our language and our reasoning when attempting to understand and explain the universe on atomic and subatomic scales.
The Elegant Universe - Greene 1999
Now, if the universe arose via a quantum fluctuation, the idea of 'where it came from' is precisely one of those things that
fails to have any meaning, and that actually includes the idea that it needs to come from anywhere. The further problem with it is, of course, that 'where' refers to a location in space, and there wasn't any.
Either way, if the quantum fluctuation hypothesis is correct, it only requires the uncertainty principle to address this. A rare statistical anomaly will suffice. It's only needed to be sufficiently large for inflation/expansion to take over. Under normal circumstances, such a fluctuation would be extremely short-lived (hence 'virtual' particles) but, given a sufficiently large fluctuation, expansion could take over and result in the universe we see today.
A singularity is a point so dense that time can not exist beyond it but if that is true then why does inflation theory support an eternal Universe ?
Well, inflationary theory comes in several flavours. Eternal inflation (the eternal universe version of inflationary theory) doesn't involve singularities in the conventional sense. You might think of each universe arising as a black hole in another universe, which may involve other dimensions. Our universe would, therefore, be a singularity in another cosmic expanse, because from the perspective of that cosmic expanse, our universe appears as a singularity (more on this in a mo), but it has extended dimensions in ours.
I should note once again that a singularity is actually problematic in quantum mechanics, depending on what you mean when you say 'singularity'. In general scientific parlance, a singularity is simply an event that our theories can't describe or, loosely, something that causes them to break. In a certain cosmological context, it means a region of infinite density and curvature. I've already discussed with you elsewhere the problems faced with the singularity but, since those discussion were elsewhere, I'll summarise the issues here: The physical singularity arises from a treatment of the reversal of cosmic expansion rooted entirely in General Relativity. General Relativity has no problem with this event, except that it can't describe anything on those scales. Further, Quantum Mechanics suggests that the physical singularity is actually asymptotic. so it can be approached but never reached. Either way, it presents problems.
Further, the singularity, even could it exist, isn't actually an event beyond which time cannot exist, it's simply an event that cannot experience time, due to the extreme gravitational time dilation at such densities of mass. That doesn't mean there was no time before the singularity, only that the singularity wasn't subject to it.
Is the answer that this Universe began at the Big Bang and the energy came from another ?
Could be. It might simply be that the energy input to our cosmos was simply the implosion of an extremely large star. That has implications for precisely what kind of thermodynamic system we're in, of course. If your cosmos is a black hole in another expanse, then new mass/energy could be input simply by the accretion of mass/energy in the black hole in the parent system, meaning that our cosmos is not an isolated system, but actually an open one, rendering the 1LT entirely moot! That's one of the reasons I warn against erecting thermodynamic arguments regarding the instantiation of the cosmos except in response to thermodynamic arguments regarding the instantiation of the cosmos.
Though that does not explain where it originally came from.
Covered above.
One cannot use the First Law Of Thermodynamics here because what applies to within a system does not apply to the system itself.
Have a care here. I've given a reason why the 1LT shouldn't be used (two reasons, actually), but you have to be really careful how you apply this. It is certainly true that it's fallacious to insist that what applies within a system applies to the system itself (fallacy of composition), but it's equally fallacious to insist that it doesn't. This is a slightly different fallacy, the fallacist's fallacy, which is committed when a conclusion is rejected on the basis that the reasoning behind it is fallacious. The conclusion could still be true, regardless of the reasoning.
And how can a multiverse hypothesis be falsified if light is impervious to branes ?
Well, it looks like we can forget branes, assuming the B Mode polarisation observations are confirmed, so a moot point. In this case, we've just seen our very first observations employing gravity rather than electromagnetism. If this sort of gravity detection can be refined, it might be that we can see back to the Planck time and even beyond it. All we need to do is to work hard on the observations, formulate hypotheses with regard to what those observations might mean, develop predictions rooted in what we might observe if our cosmos is a black hole in another cosmos and,
voila!
[ may have asked some of these before and so apologies if I have ]
No worries. I don't think I've covered much of this ground here and, aside from loving the look of my own text, there are those here who might well be interested or provide critique or clarification, or indeed correct some of my own misconceptions regarding this material and the various hypotheses pertaining thereto.
My only problem is your propensity for driving such long posts from me in response, given that I've had to sit up for this, and it's still quite early in my recovery process fro the spinal surgery, meaning that I shouldn't sit up for too long.
That was a joke, by the way, except that I am in a bit of pain now.
Anyhoo, always my pleasure, you know that.