Discussion in 'Science and Technology' started by Ayelbourne, Feb 20, 2013.
I don't believe I used that term to describe the universe either and agree with you.
Well, the problem there is that nothing in the standard model would create variations in the expansion rate once you're past the very, very early universe (inflation theory, condensation of matter, etc). If we conjecture that there is a cosmological constant, we can conjecture that perhaps it decays, and perhaps we can conjecture that it could vary, but in reality we're just piling up assumptions and writing speculative science fiction instead of physics research.
We might as well speculate that FTL travel is possible, then that it requires a warp field, and then that highly-traveled regions of space start suffering from space-time distortions as subspace starts to break down.
The expansion of the universe was decelerating several billion years ago, then it began to accelerate again. The Standard Model accounts for this as being caused by gravity--the expansion was decelerating because of the force of gravity pulling everything together. It finally hit a "breaking point" where the expansion was no longer hampered by gravity, which allowed it to begin accelerating once more.
I cannot recall how the Standard Model supposedly accounts for that "breaking point" except by making some far-reaching assumptions about the nature of dark energy. I have an impression, however, that those assumptions would be rendered irrelevant by the existence of dark matter, the abundance of which should have counteracted that "breaking point" if it existed at the time.
From what I remember, it is related to dark energy. The sequence is something like:
1. Big Bang
2. Extremely rapid expansion (inflationary period)
3. Long-term deceleration of expansion caused by the gravitational attraction of all matter in the universe to each other
4. Accelerated expansion as the influence of gravity is overtaken by the influence of dark energy (essentially vacuum energy), which intensifies over time
This article goes into some detail about how the deceleration/acceleration was inferred from observational evidence.
I understand how it was inferred. What I don't understand is the physical mechanism the model postulates for how that actually happened. To my knowledge, I've never seen a description of the model that actually describes HOW dark energy was able to do this, in terms of a mathematical relationship between vacuum energy and the net gravitation of the universe.
That paper points out that our measurements of the expansion of the universe are insufficiently detailed or precise to be able to distinguish between models of its future dynamic behaviour. It doesn't appear to state anything about the nature of dark energy (or vacuum energy), which essentially remains a fudge factor of unknown origin.
The problem lies in the fact that quantum field theory neglects gravity, see:
^ That's again prediction of the future (although the point that QFT ignores gravity is a good one).
I'm more interested in the fact that the calculations for vacuum energy (or dark energy, for that matter) do not seem to account for the presence of dark matter. Basically, if we're taking it as a given that the universe is at least ten times more massive than it appears to be (due to clouds of dark matter floating around everywhere) then the value of vacuum energy would have to be adjusted upwards as well in order to account for the accelerated expansion. But when you project that back into the early universe, it seems to create the problem that you would need EVEN MORE energy to overcome those initial gravitational forces -- gravity's influence, after all, attenuates at a square of the distance, so vacuum energy would have had to rapidly increase in a very short amount of time to account for this.
I don't think there is a good answer for that yet. We just know that the expansion of the universe used to be slowing, now it's speeding up. Dark energy is currently our best explanation for it, even though it is imperfect and needs a lot more investigation.
If you want a 100% concrete answer, there isn't one yet.
Well, fudge factors are like lies. If you tell one, you have to tell three more to cover up the holes created by the first one.
I thought the inflationary phase during the electroweak epoch from 10^−36 to 10^−32 seconds which expanded the scale of the universe by a factor of 10^75 is supposed to have been driven by the inflaton field. I don't think that inflation theory necessarily invokes what we now consider dark energy. Yet another fudge factor it seems.
No, dark energy kicked in much later. And I don't think it's fair to call it a fudge factor. Rather, the evidence shows that the universe's expansion is accelerating; "dark energy" is just our placeholder name for the as-yet-unexplained phenomenon causing that acceleration. A fudge factor is when you massage the data to fit a desired model, like Einstein's cosmological constant, which he proposed in order to cling to his belief in a steady-state universe despite the evidence showing that gravity would cause its collapse. This is the opposite of that -- it's an attempt to explain the evidence, not cancel it out. Just because it's admittedly vague doesn't mean it's dishonest.
Yes, the theories aren't dishonest, they just somehow feel unsatisfying as explanations. Another candidate, quintessence, sort of side steps the cosmological constant problem, but it too seems like a mathematical slight of hand. Perhaps a unifying theory of quantum gravity will make everything clear, but we've been waiting quite a while now.
^Of course they're unsatisfying. Nobody's claiming they're a complete solution; on the contrary, the researchers know there's still a vast amount we don't know, and that's why we're trying to find out. Science is about asking questions, not claiming to have the answers. "Dark energy" is just a placeholder for a principle we're still trying to identify. It's like "Here be dragons" on an antique map. It's not a claim of certainty, but an admission of ignorance.
On the other hand, an equally unknown phenomenon causing a uniform redshift over vast intergalactic distances would both simplify the model and eliminate the expansion problem. The other question I've been seeking an answer to for many years now is what the data would show if we looked at the redshift ITSELF as an effect, instead of the expanding motion it appears to indicate.
Well, my basic problem with the disparity comes down to credibility.
Defense lawyer: So, Doctor Higgs, you are a nuclear physicist?
Higgs: Yes, in a manner of speaking. I don't actually deal with reactors, you understand, but the fundamental forces of physics.
Defense lawyer: So you do the same type of work as Dirac, Heisenberg, Teller, the Oppenheimer brothers, Max Planck, Neils Bohr, Murray Gel-mann, Feinmann, and many other of the brightest minds humanity has ever produced?
Higgs: Yes, I do.
Defense lawyer: And these things you measure, they are confirmed in the most sophisticated and controlled experiments in the most sophisticated and expensive particle accerlators ever built by man?
Higgs: Yes, they are.
Defense Lawyer: And these kind of experiments led to the atom bomb, the hydrogen bomb, quantum mechanics and semiconductors, which would be the basis of all our fancy iPhones and iPods, and countless other real applications, from the mundane to the sublime?
Higgs: Yes, they did.
Defense Lawyer: No further questions for this witness. I'd like to call one of the stargazers to the stand, you honor.
Judge: Counsel will not refer to astronomers as "stargazers."
Defense Lawyer: Noted, your honor. I'd like to call Doctor Hubble.
*Hubble takes the stand*
Defense Lawyer: So you claim to have witnessed the expansion of the universe.
Hubble: I wouldn't claim I "witnessed" it.
Defense Lawyer: So you didn't witness it?
Hubble: No, I just observed things that supported that interpretation.
Defense Lawyer: "Supported." Interesting word. Now, I've read your deposition, and you claim these "observations" were done late at night.
Hubble: Yes, of course. I'm an astronomer.
Defense Lawyer: And this night, I take it was a moonless night.
Hubble: Moonless nights provide the clearest skies.
Defense Lawyer: Just answer the question.
Hubble: Yes, the observations were mostly on moonless nights.
Defense Lawyer: So they were very dark nights.
Hubble: Yes, I suppose they were.
Defense Lawyer: And how far away were the events you claim you didn't witness, just observed "evidence" for. "Evidence", that's an important word, you know.
Hubble: Very, very far away. In some cases millions of light years, in some cases more.
Defense Lawyer: So more than a few blocks away?
Hubble: Uh, most definitely. Almost infinitely further away.
Defense Lawyer: So you claim you "observed" things on a very dark, moonless night from almost unimaginable distances, in the wee hours?
Hubble: I suppose one could describe it like that.
Defense Lawyer: And exactly why were you up at those "wee hours"? Just couldn't sleep? Maybe out drinking with the boys?
Hubble: No, I was working.
Defense Lawyer: Working? You said earlier that you were looking at the stars.
Hubble: Yes, that's my work.
Defense Lawyer: And this work you claim you do, it's done on top of a mountain, is it not?
Hubble: Yes, of course. That's where there's the best seeing.
Defense Lawyer: The air is mighty thin up there, isn't it.
Hubble: Yes, pretty thin.
Defense Lawyer: Not much oxygen. I imagine a man, on a dark, moonless night, can imagine he sees things that aren't exactly true.
Hubble: Oh, we take photographs.
Defense Lawyer: I imagine you do. There's a photo of Elvis and Bigfoot in the papers most every week, too. So your conclusions, they're based on shifts in the spectrum of these distant stars?
Hubble: Yes, they are, and the shift becomes more pronounced the further away the galaxy is.
Defense Lawyer: So we're talking about subtle changes in spectrum, the "color", or perhaps the exact shade of white or yellow to the members of the jury.
Hubble: Yes, and the shift is most definite.
Defense Lawyer: Doctor Hubble, I assume you are a normal heterosexual male?
Judge: Where are you going with this, defense?
Defense Lawyer: Just trying to ascertain the credibility of the witness, your honor. I assure you it is relevant.
Judge: Very well. Proceed.
Defense Lawyer: So you are a normal heterosexual male, Doctor Hubble?
Hubble: Yes I am. Been married since I was young.
Defense Lawyer: So you're no better at judging colors than I am, just red, green, yellow, brown, and blue, the normal eight Crayolas. You can't tell thiel from burnt sienna from eggshell from salmon mauve.
Hubble: We don't really do it with color chips from the paint store.
Defense Lawyer: Thank you, you may step down.
(Hubble gets off the witness stand and leaves)
(Later, during summation)
Defense Lawyer: Ladies and gentlemen of the jury, what kind of person goes out in the wee hours, stars up at the stars in an oxygen deprived environment, and thinks he's working? Then claims he's witnessed, or not-witnessed, to be more accurate, something unimaginably far away on a dark moonless night when nobody could see their hand in front of their faces, much less something of cosmic significance? He claims he was working, and well, maybe he was. I know quite a few bartenders who claim they're working that late when they're downing a few.
And he makes these claims based on subtle shades of hue, when a normal guy can barely distinguish, name, and identify six or seven colors, as anyone who's taken a husband to pick new paint will well attest, and he makes these careful distinctions in pitch darkness? It's poppycock. That's what it is.
Against that we have the world's most distinguished minds, men who split the atom and provide almost unimaginable power for peace and war, who developed the computers that run our world, and who even now probe the subatomic scale with the most sophisticated tools ever devised. Would you toss out their genius for the word of a stargazer who spent too much time in the thin air?
As a jury you have to weigh the credibility of the witnesses, and in this case the difference is stark. Both theories can't be true, and it's up to you to decide who you believe. The people who have security clearances that go on for days, or the people who admit to smoking weed and sleeping all day.
The defense rests your honor.
Red and blue shift are effects seen in the absorption lines or emission lines in spectra, which appear to be moved to longer (red) or shorter (blue) wavelengths, and which do not relate to the colours themselves, which are merely qualia of our visual system.
I just read this thinking I was in a thread about political parties. And it made perfect sense. I guess I need several days of sleep, everything appears dreamlike.
So you must've had one of those big 64-Crayola boxes, noticed that somebody got them all off by one, and thought it was an issue of cosmic, Earth shattering importance. We know what kind of problem child you were in pre-school!
Speaking of spectra, I recently ran across some webpages talking about how the obsession with making ruling engines for diffraction gratings, requiring mechanical motions so precise that steel might as well be rubber, created mechanisms and methods that fed directly into our ability to make precision semiconductors (X-Y index tables that could make nanometer-scale moves).
The obsession eased once we realized that we didn't have to mechanically carve every diffraction grating from scratch, but could just use an existing grating to press lots of copies, just like stamping a CD or DVD.
Here are a few links
Dover Motion on accuracy with a section called "Prior art" starting on page 1.
Nikon on their first engine
An amateur engine built in the UK in the 1950's
Fun stuff. I can see why it was an obsession.
Separate names with a comma.