New Clues About the Nature of Dark Energy

Jim Mansfield writes "With the Hubble space telescope no longer being serviced by NASA, it's good to see one of their hardest working and most famous satellites in the news again. According to their press release on the nature of dark energy, Einstein may have been right after all - and even if he turns out to have been wrong, it seems that dark energy is not going 'to cause an end to the universe any time soon' ... whew, that's a relief." See also a space.com story.

Comments

...End of time?

[nharmon]

If the repulsion from dark energy is or becomes stronger than Einstein's prediction, the universe may be torn apart by a future "Big Rip," during which the universe expands so violenty that first the galaxies, then the stars, then planets, and finally atoms come unglued in a catastrophic end of time.

This is quite a shift from the implosion theory that results in pre-'Big Bang' conditions causing a loop in time.

Re:...End of time?

[sbma44]

Yeah, but that theory's been out of vogue for a while. It's theoretically tidy (and therefore attractive), but I believe the last few years' astronomical data has shown the universe's rate of expansion is accelerating. Something new woulkd have to turn up for the Big Crunch to come into vogue again.

Re:...End of time?

[SashaM]

I always wonder whether the "It's accelerating so it'll drift apart in the end" folks understand basic calculus. The rate of expansion accelerating doesn't mean it will continue accelerating - the third derivative of x(t) could be negative, or the fourth, and then the fifth could be positive again. You need to know all of the derivatives to know the function itself (and even that isn't true for some functions - e^(-1/x^2) IIRC).

The future of the Unvierse

[Neuropol]

After we have all (I assume that doesn't include any creationsists) adhered to the scientific theory of The Big Bang and the beginning of the Universe as we know it, I can only think that we can begin to accept the fate of the Universe.

As dark matter destabalizes, essentially matter is pulled apart at the atomic level. Some thing tells me The Big Rip, is what we are in for.

The universal constant is a nice theory and would be the better, happily-ever-after option, but in reality it seems a little far fetched if the expansion of the Universe is accelerating. It means that eventually speed will over come matter and every thing disintegrate and get ripped apart.

Relief?

[philbert26]

If a big crunch doesn't end the universe, then heat death will. Eventually the universe will reach a state of maximum entropy, and nothing interesting will happen.

Before it gets to that stage, stars will become a rare occurance. The chain of star birth and death results in smaller stars, and once stars get small enough they become like our Sun -- too small to undergo the explosive death that would provide enough mass for future stars. Eventually there won't be enough clouds of hydrogen massive enough to start nuclear fusion.

Given enough time, current theories suggest that the universe seems to be screwed either way.

Re:Relief?

[sploxx]

Being a physics student, I really don't understand the heat death argument. The heat death argument relies on the 2nd law of thermodynamics -i.e. there can't be an entropy loss. But this is not exactly true. It is unbelievable improbable that an entropy loss occurs. If one supposes that time goes one after a heat death, there can and will be a restructuring(*) of the universe. The probability that a restructuring happens is unbelievable small. But as time approaches infinity, the probability that this happens will approach one. Of course, for us, that doesn't really matter much because we'll all dead before. (*) - restructuring here: Formation of stars a solar-system and something like an earth.

Re:Relief?

[xigxag]

It's true that entropy can decrease when matter/energy enters a spontaneously ordered state, e.g. all the gas collects in the corner of the room. In itself that's infinitesimally unlikely, yet still possible. But in the case of the universe we live in, there's an additional wrinke. The edges of the "room" are expanding faster than the speed of light. Which means, eventually, every particle will disappear over every other particle's event horizon, and it will be impossible to put them back together again.

Another person downthread alludes to the idea of surviving through increasing entropy by presumably using decreasing amounts of energy. In other words, as the universe gets older and colder, there will be, say, 1/100th the free energy available utilizable by a heat pump. So a form of alife could simply run itself 100 times more slowly and thereby experience time subjectively at a linear rate. Right? Wrong. Two problems pop up. One is proton decay, which means the building blocks of any sentient computer will eventually decay on their own. And second is the cosmic background radiation. Machines work on the principle of taking in energy and outputting it in the form of waste heat. But once the universe has cooled down to the same temperature as the CBR, it will be impossible for any machine to output waste heat. It will cease to function. There is some work being done on reversible computing which might, in the long run, be able to tackle the second problem, but not the first.

non-physical physics

[Space cowboy]

Right now we're about twice as confident than before that Einstein's cosmological constant is real,

Of course, 2x (near-as-dammit-zero-certainty) is pretty much the same as (near-as-dammit-zero-certainty)...

A lot of new physics does seem to be increasingly theoretical and "out there" on the proverbial limb. It would be good for the practical lot to catch up with the theoretical lot... unfortunately, trying to verify these out-there hypotheses seems to involve larger and larger atom-smashing accelerators. Lets just hope they don't need to find the 'Higgs Boson' (hint: ohhh WAAAY ohhh, ummm barrray :-)

Simon

Re:Dark Matter and Ether

[Aardpig]

and in very complex systems Newton can't be used (chaos)

Hang on a moment; I thought the Lorenz attractor (which is the canonical example of chaos) was based on a system obeying Newtonian mechanics.

Why would it be so strange if systems with enormous scales and very small accelarations would not obey Newton's laws?

This is the line of thinking which led Mordechai Milgrom to propose Modified Newtonian Dynamics (MOND) in the 1980s. MOND posits that Newtons second law (F=ma) is modified when the acceleration is very small. It is able to "explain" the unusual rotation curves of galaxies, without the need to invoke dark matter. It can also explain phenomena which the dark matter hypothesis can't, such as the Tully-Fisher relationship observed in the surface brightness of galaxies.

However, its important to remember that MOND cannot be considered a physical theory; it is more of an empirical modification of known physical laws (like the Lorentz transformation was), which still awaits a physical explaination.

Re:Einstein was wrong anyway

[GMFTatsujin]

This whole "Eistein was right after all" angle is misinformed. He wanted a static universe because that was the historic conception of the universe. His own science didn't allow for it, but he wrangled an equation for one out of it anyway. Turns out he was wrong, is wrong, and will always have been wrong. Einstein's motivation for putting in the cosmological constant was ideological, not observational -- and that's a recipe for Dumb Science.

Dumb Science isn't "right after all," no matter how much you respect the guy who came up with it.