If you can read this, either the style sheet didn't load or you have an older browser that doesn't support style sheets. Try clearing your browser cache and refreshing the page.

(Some Guy)   Cosmologists still trying to figure out dark energy. "Frankly, it's vague to everybody, even us. There's lots of other kinds of theories, but none of them are even appealing," says Sheldon about the Big Bang theory   (sbpress.com) divider line 59
    More: Interesting, dark energy, cosmologists, theory of everything, spiral galaxy, mass-energy, expansion of the universe, Brookhaven National Laboratory, national laboratory  
•       •       •

1437 clicks; posted to Geek » on 11 May 2011 at 8:45 AM (3 years ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



59 Comments   (+0 »)
   

Archived thread

First | « | 1 | 2 | » | Last | Show all
 
2011-05-11 08:48:18 AM
Link farked already?
 
2011-05-11 08:56:42 AM
Bazinga!
 
2011-05-11 09:02:53 AM
Something HAS to be holding the universe together. That or we really missed something, somewhere.

/decimal point, some mundane detail.
 
2011-05-11 09:03:32 AM
Methinks we don't truly understand gravity. For example, where is the opposite but equal force to counteract me being accelerated into my chair at 1 G?
 
2011-05-11 09:06:30 AM
Its being pushed against you right now. Its why you aren't falling into the Earth. Your chair is returning the force. The same if you are sitting on the ground.
 
2011-05-11 09:15:29 AM

Marcus Aurelius: Methinks we don't truly understand gravity. For example, where is the opposite but equal force to counteract me being accelerated into my chair at 1 G?


That is a form of electromagnitism actually. The electron cloud of the atoms in the chair is repelling the electron cloud of the atoms that make you up. Likewise the nucleolui of the atoms in the chair are repelling the nucleolui of your atoms.

Because each individual atom is so small, the force generated is only noticeable when you appear to be touching the chair on a macro level.
 
2011-05-11 09:22:44 AM
It's amazing what is being taught in beauty school these days.
 
2011-05-11 09:22:58 AM
Yet somehow the Reapers are (probably) using it to make stars age faster than they should. :-/
 
2011-05-11 09:29:57 AM

enforcerpsu: Something HAS to be holding the universe together. That or we really missed something, somewhere.

/decimal point, some mundane detail.


I hate to say it, but I do think some significant fraction of dark energy/dark matter will turn out to be a limitation only of our current instruments and not a radical overhaul of physics.

Don't get me wrong, I'm sure the framework and our understanding of the universe will grow significantly in the coming decades and we're going to discover amazing new things. But as an example, just discovering that neutrinos have a small but definite mass has serious implications for our understanding of dark matter, and we've known about their existance for decades.
 
2011-05-11 09:35:51 AM
Dark Energy. 21st century Aether.
 
2011-05-11 09:36:53 AM
I probably understand more of this stuff than 99% of the planet (which means I understand about 1/1000 of what the people who work on the stuff actually understand) but the whole "dark" explaination has always bugged the hell out of me - its like a BS detector thats not quite sounding off, but damn it if the needle isnt moving in that direction.
 
2011-05-11 09:37:02 AM
Wasn't there a theorist who put together a different cosmological structure that did away with Dark Matter & Dark Energy? I could have sworn I saw it posted in this very forum but my google-fu is weak.
 
2011-05-11 09:44:23 AM
 
2011-05-11 09:47:21 AM
OK, without any background or justification (facts) for it here's my explaination for why it was originally slowing down but is now accelerating:

A)The universe is actually older than we think it is (hypothetical)
B)Mass is converted to energy (photons) during fusion in stars (fact)
C)Photons actually have some non-zero mass (pure hypothetical)

As the universe has aged its gravitational mass has been converted to energy (photons) which have been moving away from the universal center - bringing some nonzero amount of mass, and this gravitation attraction, with them. At some point in the past the aggregate mass of the photons which have left the observable (but not gravitational) universe exceeded the gravitational mass of what remained behind. The effect is that the gravitational "pull" from these distant photons has exceeded the gravitational pull of the remaining mass thus accelerating the expansion of the universe.

/awaits his Nobel prize (not really)
 
2011-05-11 09:55:14 AM
Because Odin commands it.

//thought it would have been obvious.
 
2011-05-11 09:55:15 AM

Fizpez: the whole "dark" explaination has always bugged the hell out of me - its like a BS detector thats not quite sounding off, but damn it if the needle isnt moving in that direction.


What, exactly, is BS about it? The scientists are being 100% honest that they haven't the faintest idea what it is. TFA flatly called it a placeholder, and no astrophysicist would disagree with that.

What they do know is that SOMETHING is DRIVING the universe's expansion, and from observations they've estimated how much energy it is. Conceptually, this part isn't any more sophisticated than observing a baseball shot out of a pitching machine and then working backwards to roughly calculate how much energy the machine put into the ball. But that's as far as they've gotten, and "energy" is a very big umbrella. It doesn't radiate light, so of course it's dark. It's energy (as opposed to matter). Dark. Energy. Dark energy. There's a whole lot of WTF, but where's the BS?

If only everyone else in the world was this honest about the limits of their knowledge. Fark wouldn't have a Politics forum, but I'll get by without that.
 
2011-05-11 10:07:54 AM

dragonchild: Fizpez: the whole "dark" explaination has always bugged the hell out of me - its like a BS detector thats not quite sounding off, but damn it if the needle isnt moving in that direction.

What, exactly, is BS about it? The scientists are being 100% honest that they haven't the faintest idea what it is. TFA flatly called it a placeholder, and no astrophysicist would disagree with that.

What they do know is that SOMETHING is DRIVING the universe's expansion, and from observations they've estimated how much energy it is. Conceptually, this part isn't any more sophisticated than observing a baseball shot out of a pitching machine and then working backwards to roughly calculate how much energy the machine put into the ball. But that's as far as they've gotten, and "energy" is a very big umbrella. It doesn't radiate light, so of course it's dark. It's energy (as opposed to matter). Dark. Energy. Dark energy. There's a whole lot of WTF, but where's the BS?

If only everyone else in the world was this honest about the limits of their knowledge. Fark wouldn't have a Politics forum, but I'll get by without that.


Wasn't calling BS - just saying that it was like a BS detector - something about it just doesnt ring true for me - and please, I admit I know tons less than these guys so its really just, like, my opinion man....

/dude
 
2011-05-11 10:17:23 AM
This (new window) is the best talk meant for the general public on dark matter/dark energy that I have seen. It is an hour long but worth it. (not to be rude but some of you have no idea what you are talking about.)
 
2011-05-11 10:18:40 AM

Fizpez: Wasn't calling BS - just saying that it was like a BS detector - something about it just doesnt ring true for me - and please, I admit I know tons less than these guys so its really just, like, my opinion man...


I'm not giving you a hard time; I'm just putting this all in plain terms. I'm no expert either, but our current understanding of dark energy is quite simple precisely because the best experts know so little about it.

Again, visualize the baseball shot out of a pitching machine. We basically have a perfect understanding of all the forces nature can exert on a baseball on Earth, so we can generally predict how fast it will go and where it will land. With computers, we can do that for the vast majority of its path. But suddenly -- whoa! -- the baseball jumps in mid-air, almost like magic. We know it's real; we tracked the ball's flight and the jump is right there in the data. Working from the data, we can use the laws of physics (namely, conservation of energy) to figure out just how much energy this mysterious force exerted on the ball. We can verify it exists and how much there is of it; we just know zip about what it is.

That's an analogy for dark energy, really. Some astronomers were observing some distant supernovas and noticed they all hit the throttle away from us like they smelled your mom or something. They measured the acceleration and, working from that, know how much energy is out there pushing stuff away from us. That's about as far as they've gone, at this point.
 
2011-05-11 10:28:09 AM
images.wikia.com
 
2011-05-11 10:29:20 AM

Non-evil Monkey: That is a form of electromagnitism actually. The electron cloud of the atoms in the chair is repelling the electron cloud of the atoms that make you up.


Not just electrostatic repulsion, but Pauli exclusion: a lot of the "effective force" keeping matter stable, instead of collapsing together, is actually quantum mechanical.
 
2011-05-11 10:31:01 AM

error 303: I hate to say it, but I do think some significant fraction of dark energy/dark matter will turn out to be a limitation only of our current instruments and not a radical overhaul of physics.


You mean, the accelerating universe is just an observation error? How does "instrument limitations" explain supernova distance-luminosity relations, or the CMBR anisotropies?
 
2011-05-11 10:40:59 AM

Marcus Aurelius: Methinks we don't truly understand gravity. For example, where is the opposite but equal force to counteract me being accelerated into my chair at 1 G?


Pretty much that. Even after Einstein's general relativity, we don't understand it. Dark matter, Dark energy are just ether arguments for the 21st century.
 
2011-05-11 10:41:17 AM

Ambitwistor: error 303: I hate to say it, but I do think some significant fraction of dark energy/dark matter will turn out to be a limitation only of our current instruments and not a radical overhaul of physics.

You mean, the accelerating universe is just an observation error? How does "instrument limitations" explain supernova distance-luminosity relations, or the CMBR anisotropies?


Not at all, just that I'm not convinced that the ultimate explanation will require complete teardown of the standard model to accomodate it. The inability of current accelerators to produce the exotic particles or forces needed to explain it could be one factor. I guess I'm thinking more along the lines of dark matter rather than energy, and I'd love to be wrong.
 
2011-05-11 10:41:27 AM
wwwimage.cbs.com

Well this article makes me sound unsure

/you will now read this thread in Sheldon's voice
 
2011-05-11 10:42:59 AM

error 303: enforcerpsu: Something HAS to be holding the universe together. That or we really missed something, somewhere.

/decimal point, some mundane detail.

I hate to say it, but I do think some significant fraction of dark energy/dark matter will turn out to be a limitation only of our current instruments and not a radical overhaul of physics.

Don't get me wrong, I'm sure the framework and our understanding of the universe will grow significantly in the coming decades and we're going to discover amazing new things. But as an example, just discovering that neutrinos have a small but definite mass has serious implications for our understanding of dark matter, and we've known about their existance for decades.


I always thought the same as well. If we start finding mass in other particles, does that mean dark matter may actually be a hell of a lot less or even the "wrong" theory. Wrong is subjective as you could call whatever we are missing whatever you want.

Since we are now discovering more fundamental forces, I wonder if it will revise how the universe is held together. Gravity itself it still a big mystery.
 
2011-05-11 10:43:30 AM
Isn't this something the Quarians are trying to figure out?
 
2011-05-11 10:45:50 AM

rwfan: This (new window) is the best talk meant for the general public on dark matter/dark energy that I have seen. It is an hour long but worth it.


He has a 24-lecture course on this stuff you can buy here. Also tons of material on the blog Cosmic Variance, although I can't find a good starting entry on dark energy at the moment.
 
2011-05-11 10:47:45 AM

stuhayes2010: Pretty much that. Even after Einstein's general relativity, we don't understand it.


What don't we understand? The chair argument was already explained above-thread.

Dark matter, Dark energy are just ether arguments for the 21st century.

I hear that comment a lot, but it's pretty ignorant of how much we actually know about these subjects. Especially dark matter.
 
2011-05-11 10:51:29 AM

error 303: Not at all, just that I'm not convinced that the ultimate explanation will require complete teardown of the standard model to accomodate it.


We probably don't have to "tear down the Standard Model". The most plausible theory of dark energy remains the cosmological constant, which is just a minor modification of general relativity. (Actually, it's not even a modification - it was originally part of Einstein's theory to begin with, but he took it out when astronomers were unable to find evidence for it. Now they have.)

The inability of current accelerators to produce the exotic particles or forces needed to explain it could be one factor. I guess I'm thinking more along the lines of dark matter rather than energy, and I'd love to be wrong.

With dark matter, the most common candidates are axions and neutralinos. The former are practically part of the Standard Model already; they're a relatively obvious extension of QCD to explain the strong-CP problem. The latter are from supersymmetry, which is more speculative, but there are independent reasons to suspect that such particles may exist. Anyway, yes, it's likely that we haven't detected dark matter directly because our current accelerators can't produce it yet.
 
2011-05-11 10:54:45 AM

enforcerpsu: I always thought the same as well. If we start finding mass in other particles, does that mean dark matter may actually be a hell of a lot less or even the "wrong" theory.


Mass in what other particles?

Wrong is subjective as you could call whatever we are missing whatever you want.

Although, if "whatever we are missing" isn't matter, it would be inappropriate to call it "dark matter".

Gravity itself it still a big mystery.

At the classical level, I wouldn't say gravity is a big mystery. Quantum gravity is a big mystery, but that's not relevant for most of the gravitational phenomena we observe.
 
2011-05-11 10:56:55 AM

Ambitwistor: Anyway, yes, it's likely that we haven't detected dark matter directly because our current accelerators can't produce it yet.


Mostly what I'm getting at, and that my hunch would be that figuring out the origin of much of the dark matter(or dark energy) will be another revision to the standard model, not the upheaval of physics as we know it.

I'm going to guess you do this sort of thing for a living? I got a bachelors in astrophysics before figuring out grad school wasn't for me and took a physics job outside the academic world. More and more I'm thinking baout going back to grad school though. Thinking is fun.
 
2011-05-11 11:01:19 AM

Ambitwistor: stuhayes2010: Pretty much that. Even after Einstein's general relativity, we don't understand it.

What don't we understand? The chair argument was already explained above-thread.

Dark matter, Dark energy are just ether arguments for the 21st century.

I hear that comment a lot, but it's pretty ignorant of how much we actually know about these subjects. Especially dark matter.


How much do we know? We're still trying to find dark matter, that will answer the questions about universal slowing down. It's identical to the ether arguments of light and the vacuum of the late 1800's.

And I wasn't answering the chair discussion, the fact is we don't understand gravity.
 
2011-05-11 11:13:48 AM

mamoru: Yet somehow the Reapers are (probably) using it to make stars age faster than they should. :-/


But the question is: why?

ME3 has some 'splainin' to do
 
2011-05-11 11:16:56 AM
"...we're just going to go and look and measure the best we can and shed some light on it, get some kind of clue."

They're on the case!

stokereport.com
 
2011-05-11 11:20:50 AM

stuhayes2010: How much do we know?


First, we know a lot about what it's not: most of it can't be photons, neutrinos, brown dwarves or other baryonic matter. And it's almost certainly not gravity.

The reasons why we know it's not these things, also tell us a lot about what it is: it's a weakly interacting massive particle, probably with a mass in the TeV range. Particle physics has long proposed that such particles exist, for reasons entirely independent of astrophysics. As I mentioned in another post above, the leading candidates are axions and neutralinos.

The observational evidence which allows us to rule out some candidates and focus on others include galactic velocity rotation curves, early universe structure formation at the scale of galactic clusters and above, anisotropies in the cosmic background radiation, collisions between galaxies, direct non-detection results (what we don't see tells us something about what it can't be), and so on. Together, these tell us a lot about the possible mass, interaction dynamics, and abundance of dark matter.

We're still trying to find dark matter, that will answer the questions about universal slowing down. It's identical to the ether arguments of light and the vacuum of the late 1800's.

Hardly. Ether didn't have any observational evidence whatsoever. Dark matter has plenty of observational evidence, it's just all gravitational. But we can learn a lot from gravitational dynamics, that places quite strong constraints on what dark matter can and cannot be. Furthermore, there are theoretical reasons to believe that dark matter exists, entirely independent of the gravitational evidence or implications for astrophysics.

And I wasn't answering the chair discussion, the fact is we don't understand gravity.

What don't we understand about gravity, other than its behavior at the quantum level?
 
2011-05-11 11:25:12 AM
"The expansion of the universe is accelerating, and scientists have no idea why."

The answer is obvious. (And it is probable that many cosmologists know the answer. But KNOWING the reason for something gets less grant funding than expressing puzzlement.)

Hint: landscape.

Anyone here got the degree of open mind to take it from there?
 
2011-05-11 11:43:28 AM

bookman: Hint: landscape.

Anyone here got the degree of open mind to take it from there?


Reticulating splines.
 
2011-05-11 11:57:00 AM
Since she doesn't get enough exposure, here is a picture of
Melissa Rauch in place of the usual picture of Kaley Cuoco I
usually post in threads vaguely related to THE BIG BANG THEORY:

www.wikifeet.com
 
2011-05-11 12:25:03 PM

Marcus Aurelius: Methinks we don't truly understand gravity. For example, where is the opposite but equal force to counteract me being accelerated into my chair at 1 G?


Um... the force that you exert on the planet? F=G*m1*m2/d^2- you and the Earth exert equal and opposite forces on each other. It's just that the Earth is so much larger than you it barely notices.
 
2011-05-11 12:45:29 PM
submitter is probably sad this thread doesn't have more BBT references.
 
2011-05-11 12:46:58 PM

t3knomanser: Marcus Aurelius: Methinks we don't truly understand gravity. For example, where is the opposite but equal force to counteract me being accelerated into my chair at 1 G?

Um... the force that you exert on the planet? F=G*m1*m2/d^2- you and the Earth exert equal and opposite forces on each other. It's just that the Earth is so much larger than you it barely notices.


He'r right that we don't understand what causes objects to HAVE mass, nor, I believe, have we discovered the force carrier particle for gravity. We understand really well the effects of gravity, not so much of the why.
 
2011-05-11 12:53:57 PM

Fizpez: He'r right that we don't understand what causes objects to HAVE mass


Well, that's what we're working on at the LHC. The Higgs boson, if found, will explain that. If not, well- that's one hypothesis we can discard, getting us nearer to that thorny problem.

But there's one important thing we know about gravity: it's a field that obeys the inverse square law. To claim that it has some hidden effect that doesn't behave that way is to make a rather extraordinary claim. All fields in our universe obey the inverse square law (and we don't know why that is, any more than why objects have mass). While there's much we don't know, what we do know eliminates any theory that suggest gravity behaves differently at a different scale. It's not impossible- just very very unlikely.
 
2011-05-11 01:03:48 PM

Fizpez: He'r right that we don't understand what causes objects to HAVE mass,


It hasn't been experimentally confirmed, but the Higgs mechanism is a pretty good bet.

nor, I believe, have we discovered the force carrier particle for gravity.

We will never detect an individual graviton particle. Gravity is too weak for that. We might, at best, detect the indirect imprint of a whole bunch of gravitons near the Big Bang, if we're very lucky. But regardless of whether or not we detect gravitons, general relativity still holds fine on any classical level. As far as every gravitational phenomenon we can currently observe goes, general relativity continue to be a remarkably accurate explanation.

We understand really well the effects of gravity, not so much of the why.

We're never going to know "why" any fundamental law of physics is true. This applies to every fundamental physical theory, not just gravity. Why single out gravity?
 
2011-05-11 01:05:51 PM

t3knomanser: you and the Earth exert equal and opposite forces on each other. It's just that the Earth is so much larger than you it barely notices.


"your Mom" joke goes where?
 
2011-05-11 01:17:04 PM

t3knomanser: All fields in our universe obey the inverse square law (and we don't know why that is, any more than why objects have mass)


I hate to be pedantic with somebody doing such a good job of explaining most of this stuff, but two niggles:

1) The strong nuclear force doesn't obey the inverse square law.

2) The Newtonian explanation for an inverse square law would be that the force carriers (such as photons or gravitons) spread out spherically; and if space is Euclidean and three dimensional, the surface of the sphere grows with the square of the distance from the source, so the flux of the force carriers falls at the same rate.

Of course, GR tells us that spacetime isn't perfectly Euclidean, and correspondingly gravity doesn't follow a precise inverse-squared law. But that's OK.

Is there anything wrong with that explanation from a post-Newtonian perspective?


t3knomanser: While there's much we don't know, what we do know eliminates any theory that suggest gravity behaves differently at a different scale. It's not impossible- just very very unlikely.


^This. Given the amount of data, it's *very* hard to modify the theory of gravity to (a) still be consistent with the known data and (b) not be completely arbitrary. For instance, MOND gathered a lot of interest as a possible substitute for dark matter, until the Bullet Cluster shot it down.
 
2011-05-11 01:35:55 PM
I love discussions like this.

I don't have anything to add, that isn't already being addressed by those more knowledgeable than myself, so I'm just gonna curl up with a beer and see if I can keep up.
 
2011-05-11 02:35:44 PM
If the universe has a finite diameter, then it is a bubble of spacetime bounded by nothingness. That would mean that while the universe has a measurable diameter, it has a perimeter of zero - much as a record whose outer edge was spinning at the speed of light would have a perimeter of zero (due to relativistic contraction). Since acceleration and gravitation are functionally interchangeable, the math is pretty much the same (just more dimensions).

Therefore the universe's edge is a singularity. No matter what direction you travel in, you're curving toward the same point - a massive singularity that is of zero size, yet 'surrounds' the entire universe. As matter moves from the center of the universe toward the edge, it's falling into a gravity well, and therefore accelerates. From our perspective, everything moving outward speeds up.

I call the singularity that serves as the universe's perimeter the 'pangularity', from the Latin 'pan' meaning 'all', an all-surrounding singularity (from a certain point of view).

Came up with that nutty idea back when I was 15. Decided I was wrong because back then we thought everything was slowing down. Was surprised when the newer observations demonstrated everything accelerating. Probably wrong somehow, but I still like the idea.

You're welcome, scientists.
 
2011-05-11 02:43:54 PM

tankjr: Dark Energy. 21st century Aether.


Aether. 19th century God.
 
2011-05-11 03:23:32 PM

SordidEuphemism: Wasn't there a theorist who put together a different cosmological structure that did away with Dark Matter & Dark Energy? I could have sworn I saw it posted in this very forum but my google-fu is weak.


Modified Newtonian Dynamics (MOND), Mordechai Milgrom, perhaps? Wiki's got lots on this.

I read a review of MOND, saying "it fails, but in an interesting way".

Geoff Burbidge compared dark matter and inflation to the old "epicycles", and that was even before they knew about the "dark energy" accelleration.
 
Displayed 50 of 59 comments

First | « | 1 | 2 | » | Last | Show all



This thread is archived, and closed to new comments.

Continue Farking
Submit a Link »






Report