PHYSICS APPLECART UPSET as dark energy disappears, Universe slams on brakes In-the-dark astrophysicists now think there's probably less dark energy knocking about than was previously thought – which may suggest that the universe is expanding at a slower rate. That's at least the latest thinking on the subject to come out of the University of Arizona, whose team of astronomers claimed that their …
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They should stop being so adamant that their theory du jour is the ultimate final truth. That's too often how it's presented, almost as if their conclusions can be chiseled into stone tablets...
Need more "we current have evidence that suggests" and less "is".
If I want self-confident assurance of ultimate truth, then I'd be checking out my local church.
That is quite the way they've been acting, particularly with respect to dark matter, and estimating the size of the universe. My major started out there before I migrated to the liberal arts. I got the concepts, just couldn't do the math. One thing that was quite clear was that the whole cosmological understanding is quite a house of cards with lots of places for error that are discounted. That isn't to say it isn't our best understanding of the data collected to date, just that everybody acts like certain things are better proven than they are.
>Then the reporting of the press releases gets even further from the actual results.
So true. Yet, much funding comes from people who seek the certainty those press-releases provide and we end up with a cosy conspiracy of misinterpretation and exaggeration.
I'm not so sure about science being self-correcting either. How do you know it isn't lurching from one misunderstanding of reality to another? Is that being taken on blind faith? Maybe I'm just a sceptic.
In Jimbo's expanding bag of trivia, we read:
The cosmological constant has negative pressure equal to its energy density and so causes the expansion of the universe to accelerate. The reason why a cosmological constant has negative pressure can be seen from classical thermodynamics; Energy must be lost from inside a container to do work on the container. A change in volume dV requires work done equal to a change of energy −P dV, where P is the pressure. But the amount of energy in a container full of vacuum actually increases when the volume increases (dV is positive), because the energy is equal to ρV, where ρ (rho) is the energy density of the cosmological constant. Therefore, P is negative and, in fact, P = −ρ.
This sounds like a first-semester argument (a "sophomorism"?) to me, where imagery not really appropriate to the case at hand (in this case, classical thermodynamics and its macroscopic values applied to empty space in a FLRW universe) is used in a handwaving fashion to make a point, which is then underscored with mathematical formulae at high school level. A kind of student party trick, or stuff at second degree of freshness from a cranky paper.
On what does this pressure act (frankly, it would need to push matter into a direction orthogonal to the recognized three dimensions)?. What's up with the gravitational effect of that nonzero energy (the 73% percent, natch), which would act as a tension on empty space? Why does one have an effect, but not the other?
I DEMAND AN EXPLANATION!
The simplest of explanations rendered with Media and IT for AI is in a type of Kind Magic, for such cosmological speculation appears to be a prime base setting for the creation of universes and that which is generally known of as life and existence.
And did you misspeak, Mark 85, with .....
In other words.... I don't think the experts really know
..... and actually mean to share ...... In other words ..... I think, and the experts don't really know.
imagery not really appropriate to the case at hand (in this case, classical thermodynamics and its macroscopic values applied to empty space in a FLRW universe)
Why would classical thermodynamics NOT be an appropriate analogue to an FLRW universe?
From http://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric#Interpretation:
The first equation can be derived also from thermodynamical considerations and is equivalent to the first law of thermodynamics, assuming the expansion of the Universe is an adiabatic process (which is implicitly assumed in the derivation of the Friedmann–Lemaître–Robertson–Walker metric).
So either (a) more than one Wikipedia entry related to physical cosmology is tainted, or (b) the standard model of cosmology is analogous to a classical themodynamic system.
I'm not an expert on cosmology, thermodynamics, or Wikipedia, but as I've seen, heard, and read physicists use classical thermodynamics to explain cosmology in other media, I'm leaning towards believing that Wikipedia's got this one right, or at least consistent with prevailing theory.
First of all, the universe is under no obligation to make sense to you. Second, read A Universe from Nothing, by Lawrence Krauss. There is only about 1% of the amount of normal matter in the universe to explain its gravitational behaviour. Gravitational lensing finds dark matter, bringing us close to 30% of the mass needed. Dark energy, remember (e=mc squared), makes up the rest of the mass and coincidentally, accounts for the acceleration in the expansion of the universe. I don't know how this new info will affect those calculations (perhaps the universe is older than 13.72 billion years?).
First of all, the universe is under no obligation to make sense to you.
But the description better had otherwise we are just telling ghost stories to each other.
makes up the rest of the mass and coincidentally, accounts for the acceleration in the expansion of the universe
But there is the rub. Mass or Energy means gravitation means deceleration, not acceleration.
As matter, it means gravity and deceleration, as quantum vacuum energy, it means expansion. That's why the distinction between dark matter, centred around galactic clusters, and dark energy, in "empty" space. Nobody knows what either is, but their effects are measurable. Read Krauss for details; I have already gone past the end of my knowledge of cosmology and particle physics.
The pressure acts against gravity, and it is a pressure not a simple force because it acts throughout space (i.e. has a value which is proportional to any enclosed area through which it acts.) So it applies to the three ordinary spatial dimensions.
Obviously I'm not intelligent enough to perceive that the argument is a sophomorism, so it just makes sense to me. If I was really clever, I wouldn't be able to understand it.
"Pressure" is a concept that is the statistical result of stuff bumping into each other and exchanging momentum via electrostatic force. Here we have space pressuring against stuff because someone applied a thermodynamic argument about closed containers with constant internal energy to circumscribed volumes in empty space being filled with energy isothermically via a magic energy faucet from nowhere (gridfire, anyone?). How does this make sense?
So it applies to the three ordinary spatial dimensions.
Really?
Obviously I'm not intelligent enough to perceive that the argument is a sophomorism
You should start then or politicians and their court sycophants will sell you ANYTHING.
""Pressure" is a concept that is the statistical result of stuff bumping into each other and exchanging momentum via electrostatic force."
Now I know you're just trolling. You have it exactly backward.
Pressure, the concept, is defined as force per unit area. There is nothing in that about electrostatic force or momentum transfer. If I take two diamond anvils and apply force, there is a pressure at the interface but no momentum transfer. The pressure is RESISTED by the electric field of the electrons; the electric field is not the pressure.
But, going a step further, what really causes, say, atmospheric pressure? It is caused by the gravitational force acting on the molecules of the air and pulling them inwards towards the centre of the earth. The reason that the air doesn't collapse to a neutron soup is indeed that electric field surrounding the atoms, but the pressure is caused by gravitation. In a neutron star, the gravity is high enough to overcome the electron fields of atoms, and the nuclei condense to a liquid. The matter of the star doesn't collapse to a point because of complex interactions between its baryons, but it has a pressure at every point and the pressure is caused by gravitation, not by the electroweak or strong forces.
So now we have vacuum energy. Like gravitation it behaves as a field which is not mediated by photons or other particles that feel the EM force. Also like gravitation, its effect is to create a pressure on masses of particles. But, unlike gravitation which is attractive between particles, it causes a repulsion, or by extension a negative pressure. And just as the net force vector on a particle due to gravitation is in the normal three spatial directions, the repulsive force will produce a vector on a particle in the normal three spatial directions.
I'd say it is hardly rocket science, but of course our rocket science is generally on too small a scale for vacuum energy to affect orbital calculations.
Now I know you're just trolling. You have it exactly backward.
Excuse me? You really want to go back to check these physics books and statistical mechanics. But feel free to accuse me of "trolling" if that ups the ego.
Pressure, the concept, is defined as force per unit area. There is nothing in that about electrostatic force or momentum transfer.
You may actually start to get into that "reading" thing and find out that I didn't say anything like this. Anyway...
but it has a pressure at every point and the pressure is caused by gravitation
Your concepts are very unclear. As you said yourself: pressure is per unit area. Can't have pressure at a "point", captain.
But, unlike gravitation which is attractive between particles, it causes a repulsion, or by extension a negative pressure.
You seem to set out with what you want to prove. There is negative pressure because there is something generating negative pressure. This isn't helping.
the repulsive force will produce a vector on a particle in the normal three spatial directions
But as the vacuum is everywhere, where exactly is that vector pointing?
Yes, I've been back to check my physics books (well, actually my collection of back astrophysics papers). But not statistical mechanics because it is irrelevant here.
You may actually start to get into that "reading" thing and find out that I didn't say anything like this.
This is the disadvantage of your posting AC. It's possible that I have attributed to you the words posted by another AC.
Your concepts are very unclear. As you said yourself: pressure is per unit area. Can't have pressure at a "point", captain.
Well, I agree my terminology was a little sloppy there but this is a blog not a thesis and I think any normal person would understand what I meant. Colloquially when we say "any point on the Earth's surface", or "any point in the universe", we mean a very small defined area or volume, not something of zero size.
In any case, it being impossible to have a meaningful discussion with an unknown number of AC nitpickers who presumably don't think much of people like Saul Perlmutter, I leave you in possession of the field, though it's a somewhat Pyrrhic victory since your desire to score debating points means that you're missing some interesting science.
My knowledge and understanding of this subject is severely limited by a tiny brain, so I will stick to asking a question.
Is it possible that there is some form of naturally occurring anti-gravity that pushes the fabric of space apart rather than bringing it together (perhaps at the baryonic level)?
"Is it possible that there is some form of naturally occurring anti-gravity that pushes the fabric of space apart..."
Or, to broaden that comment: Is it possible that something besides "dark matter" and "dark energy" are behind these anomalies that have been observed?
I am no expert in physics or cosmology, I just have an amateur's fascination with the subject, but every time I hear those terms, I am reminded of Isaac Asimov's essay "The Planet That Wasn't" in which he describes the search by early 20th century astronomers for the planet Vulcan which, based on observed perturbations, they were sure existed inside Mercury's orbit. I don't remember the details, but it turns out something in Einstein's theories explained the anomalies perfectly and eliminated the need for a planet.
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I won't pretend to understand what some idiot thinks they wrote on Jimmy-Bob's wonder.
From my time at uni, the simplest explanation is:
Having calculated the speed at which various objects appear to be moving, and having determined that we all seem to be moving apart (everything observed so far has a red-shifted spectrum), when you calculate the mass of the universe based on our observations, all of the objects exceed escape velocity for the mass density of the universe.
Have an up vote because I'm in a contrarian mood at the moment and you have two down votes. But give the free beer to some random person. I don't drink the stuff. Much more than half a glass and I'm ready to hurl the technicolor yawn.I much prefer Gin and Tonics. Those I can suck down by the 32 oz Moose cup.
It is entirely possible that the 'new calculations' will reveal that the Universe is like a roller coaster would be in the absence of friction: Outward to a certain stage, then back in to a singularity, followed by another big bang, and the process starts again, ad infinitum. Huh? I like this scenario much better than entropy.
I like that too but there still has to be a first big bang (at least in human logic) like with life, if it did not start here it still had to start somwhere. I like the multi universe theory more but sometimes I think we need to know more about the limitations of our brains to have a chance of understanding the universe,
Thanks. The thing is, we don't understand time. Not entirely. We know it operates at different rates in different places, and there is no privileged position, but--I'm out of my depth here. We probably -are- sitting on a giant's back or some big turtle or something. Maybe the Universe is a big Mobius strip, huh?
That is assuming that whatever the successive big bangs and big crunches take place in, "time" is a meaningful attribute of it.
The fact that there is anything at all is the thing that has to be "explained" but may well be as beyond a human understanding as the world outside its pond is to a goldfish. Given the initial inexplicability of existence, the inexplicability of time is just a footnote.
Most physicists prefer a "flat" universe, one in which the expansion slows and asymptotically approaches but never reaches zero and subsequent collapse. That way the sum of all the energy is zero and you don't have to figure out where the energy came from to create the universe in the first place.
"Maybe the Universe is a big Mobius strip, huh?"
My personal experiences lead me to believe it is Torus shaped.
During one very deep meditation on the fabric of space-time I delved into the realm of the very small, at a certain point I realised that the small was representing the large and that I had 'wrapped around' so to speak. As I continued to go smaller I ended up back where I started - only by this time I was 'looking' at the back of my own head*. YMMV.
*I've never tried this thought experiment by going 'large' first, I expect it would end up like I was looking in a mirror.
So did Einstein, hence his creation of the "Cosmological constant" which he later called the worst mistake he ever made. The problem is, based on what we think we understand about physics, the observations just don't support it. Of course, from a Cosmological viewpoint, our observation baseline for physics is even worse than the climate baseline is for AGW.
What has changed in the Universe?
If those supernovae are caused by the same physical phenomena, under the same circumstances, creating the type... What Has Changed?
Whether we're up for heat-death or contraction, or gravity-pit oblivion is ultimately a minor, if not moot question compared to this, given that it's based on several constants which should be, well.... constant.. as far as current theory goes. If there's two populations based on distance = time, we either measured wrong, or *something* happened around the border between the two.
Nothing has changed, this is the basic assumption (remember the "alpha changes!" flap around when Bush II went to Afghanistan ... nothing concrete ever came of that - the universe seems set in most ways)
However these star crackers change their behaviour as the universe ages, kinda like with your bones. There is more metal around at later stages of the evolution for example. So all the physics are the same, but actual behaviours differ. Kinda like you can have hypernovae but only at early stages of the universe.
"I.e. The big crunch is not the reverse of the big bang, whatever that was. Big bang, very low entropy - big crunch, very high entropy."
Er... no. opposite of the "big bang" is *exactly* what "big crunch" means.
"maximum entropy" is the point halfway between bang and crunch the universe reaches before it starts collapsing again into a low-entropy crunch. in that model after maximum entropy all energy and matter vector inwards towards the singularity "crunch" point. entropy/heat gets converted back into ever more dense energy forms (matter being one of those) in reverse of what the bang did. nice and symmetrical.
you may be confusing "crunch" with the "heat death" hyothesis where everything gets converted into entropic so-called "heat" energy which just keeps expanding into an empty infinity. if you want to survive the end of the universe you really dont want endless nothing to be the destination.
it all depends either on what the interior of a black hole is, or how much matter+energy can be found though.
Wrong. The "big crunch" is max entropy as at that point, everything has collapsed gravitationally to maximum mixture. At the "big bang", gravitational clumping is minimal, so entropy is very low.
you may be confusing "crunch" with the "heat death" hyothesis where everything gets converted into entropic so-called "heat" energy which just keeps expanding into an empty infinity
"Heat death" means that the universe ages without crunching. Entropy increases constantly until every cm³ of space is just a uniform warm bath of heat and no useful work can be done anymore (this happens after the last black hole has evaporated and possibly the last proton has decayed and/or rest mass has gone to zero for some reason or other). Ultimately, you just have very-low energy photons, and the universe continues to cool off as it expands (OTOH, there would be nothing left to even build a clock with, so is there actually TIME at that point?)
At the Big Bang, as I understand it, there isn't any matter that feels the gravitational field, so nothing opposes the initial, superluminal inflation. (As the universe as a whole isn't doing any work - it isn't expanding "into" anything - there isn't a problem with the thermodynamics of this). As soon as particles start to condense out and there is any clumping at all, matter starts to accumulate under the influence of gravitation and we get the local concentrations called "stars" that create temperature differences which allow them to accomplish work on other things, though overall the net entropy of the universe is of course continually increasing. Without asymmetry arising soon after the Big Bang, there would be no temperature variation in the universe and the entropy would be constant (and very large). Although there are theories, the asymmetry is yet to have a completely convincing explanation, unless of course it was God sticking a finger in and stirring the primordial soup, which has its own ontological problems.
At the Big Crunch, at a certain point on the way down the matter of the universe would presumably be a single symmetrical liquid of various particles in random states so entropy would be very high - there is no possibility for work to be done because everything is at the same temperature. If the Big Crunch collapses to a singularity or some other object to be determined, it may start a new bounce - in which case any lack of symmetry ends up recreating a universe with different parts at different temperatures and off we go again. Or it could conceivably just cease to exist, like a cosmic Pequod going down a cosmic plughole. In either case, there is a point at which the entropy just disappears, which makes sense because entropy can be seen as loss of information, and as the universe approaches the Big Crunch all possibility of information being retrieved simply vanishes.
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"Why is it so difficult to buy high-wattage CFLs in the UK?"
Who cares? You can get 7000+ lumen LED bulbs for a few quid now, that look more attractive, to my eyes emit a nicer light and use even less juice than CCFLs. The newest "filament" type closely resemble an incandescent bulb.
So, let's see if I understand this correctly.
Scientists theorise from observation that the universe is expanding at a certain rate but can't identify enough matter/energy to account for it. So they postulate some unobserved dark matter/energy.
Now, they postulate that the amount of theorized and unobserved dark matter/energy must be less than they thought so the universe must be expanding more slowly than first theorised from observations.
Maybe there's some even darker matter/energy to account for the missing dark matter/energy?
My head hurts but I can't tell if it's exploding or imploding. Either way, it's dark in there so it doesn't really matter.
Coat, The one with the deep, dark pockets ------->
EDIT: My wife just said it's like a seeing a bus going down the motorway at 200MPH and the engine obviously can't make it go that fast so it must have another invisible engine helping out. But now we think the magic unseen, invisible engine is much smaller than we thought therefore the bus isn't actually going at 200mph after all. My had still hurts.
Your wife is obviously an intelligent person with a flair for analogy. However..
Isn't the point that the 200MPH bus is being timed by the mileposts, and someone has just announced that those mileposts may have been planted by two different road gangs with different measuring sticks, and possibly aren't very accurate anyway?
Feynman observed that anti-particles are just particles moving backwards in time. This explains why we only see very few more-recently produced ones; the original other half of The Ultimate Free Lunch went the other way in time.
Once one can hoist aboard the above, then extend it to other dimensions. Maybe something will shake out.
But it does. Position uncertainty means non-virtual particles may be faster than c sometimes. Special realtivity means that in that case there are reference frames where these particles go "backwards in time". Turns out that these horrors are exactly antiparticles going forwards in time. So there is a good reason for having antiparticles and they do ferry information from the future in a certain sense. It's very satisfying when you realize that a closed loop (particle pair creation and annihilation) in a Feynman diagram can be seen as the same particle going forward, then backward in time.
One of the most frequent comments throughout science is some form of "We used to think...". Universal expansion is not immune to that comment.
Prior to the big bang it is said the entire universe was contained in a super tiny enclave and nothing else existed. For something to be tiny there has to be something large. Since there was nothing else to be large the entire universe had no size. For something to be fast there has to be something slow. Same thing. There was no speed. The bag bang, if that is what happened who knows why, could have occurred in place, initiating motion for its individual particles that had been contained motionless relative to each other, and starting the process of assembly and dis-assembly , from the interplay of gravity energy and motion energy, that continues and will continue. Or not!
The bag bang? Are you suggesting that some playful Creator 'startled' the universe into being?
Absolutely, there are traces of the Universal Crisp Packet going back right to the moment before the Bag Bang, although scientists are unsure at this moment whether Salt-and-Vinegar, or Cheese-and-Onion were the catalytic ingredients.
Thank you for the funding used to provide researchers dosh to figure out a number based on some modelling assumptions. That money has run out now and can we have some more please?
We can use it to tweak some base assumptions and need to recalculate to consequences on the number already figured out earlier as it now looks wrong.
Ta velly muchly
Big Bang Research Team
I'll happily be corrected on this, out dated knowledge + lack of time to fully read the article.
When the mass of the universe was measured and found that 90% of matter was not visible, hence the sexy name "dark matter", maybe there was something fundamentally wrong with either the measurement (maybe 90% of the universe is outside of our visible range) & / or our calculations are wrong (damned decimal point!)?
No, it is very simple. Dark matter is needed to explain the angular velocity of stars in galaxies, because it is much too high based on the mass of the visible components. Or, in simpler language, galaxies are rotating much too fast and ought to break up. We can be pretty confident about the invariance of gravitation and the applicability of classical mechanics. So there is something in galaxies which feels the gravitational field and of which there is much, much more than the visible matter.
It doesn't matter whether the "missing" mass is exotic dark particles or something else, it's there. What's more the evidence is that the missing matter is not at the galactic centres but in large more or less spherical haloes centred on the galaxy, which means that whatever it is, we can see right through it. Hence, dark matter.
Explains galaxy rotation without dark matter, also explains a lot of other anomalies such as the anomalous orbit of Mercury and the Pioneer anomaly.
Interestingly a lot of physicists are beginning to see that dark matter might in fact not exist at all as MiHsC accounts for all of the "missing" mass.
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