Nobel Prize for Dark Energy trio

Saul Perlmutter, Brian Schmidt & Adam Riess

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Nobel Prize for Dark Energy trio

#1  Postby THWOTH » Oct 05, 2011 6:42 pm

geek.com wrote:Dark energy physicists nab Nobel Prize for Physics

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No, not that kind of dark energy

Dark energy is a mysterious phenomenon in the study of the physical universe. Its theoretical existence has been bandied about for years, with little understanding of what it actually is. But three astronomers who made the study of dark matter their lives’ missions have helped to shed some light on the mysterious darkness. As a result, they have snagged the 2011 Nobel Prize for Physics.

Dark energy refers to a curious phenomenon. Scientists know that the universe is expanding. That has been well-documented for years. But the part that left many scratching their heads was that this expansion is actually picking up in pace. The idea is that something must be making it do that. While it still isn’t known exactly what the force is that causes this acceleration, dark energy is the term that scientists use to describe it.

Saul Perlmutter, Brian Schmidt, and Adam Riess, all astronomers, have spent years collecting data, attempting to document and understand the concept of dark energy. They were the first astronomers to observe the increasing expansion of the universe over 20 years ago, when the light from distant supernova were weaker than expected.

After coming to the conclusion that this meant the universe was expanding faster, they took it upon themselves to largely carry the torch in the continued study of dark energy since then. It is now thought that dark energy makes up about 75% of the universe. 21% is supposed to be dark matter, with the rest being ordinary matter.

In presenting the Nobel Prize to the group, the Academy stated that their work has “helped to unveil a universe that to a large extent is unknown to science. And everything is possible again.” ...

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Reading about the prize awarded today led me to wondering; what does it actually mean to say the universe is expanding?

:dunno:

(Then again, perhaps it's not be that tricky and I've just been spending far too much time on the William Lane Craig thread!)

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Re: Noble Prize for Dark Energy trio

#2  Postby Dudely » Oct 05, 2011 7:04 pm

It means that everything in the universe is getting further apart, relatively speaking. It's kind of like bread dough with raisins or something in it. As it sits on the counter to rise the raisins get further apart. The size of the 'dough' doesn't matter- it could very well be infinite. (Whether or not the universe is infinite, and what that means for expansion is a fascinating subject that I won't go into right now, but trust me- it's pretty cool stuff)

Remember, you can't think about the universe in a normal three-dimensional way because it IS the normal three dimensions. Asking what it's expanding into, for example, is like asking what happens when you go south of the south pole.
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Re: Noble Prize for Dark Energy trio

#3  Postby tuco » Oct 05, 2011 7:08 pm

So, if everything is getting further apart then new matter is being created, new bread?
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Re: Noble Prize for Dark Energy trio

#4  Postby newolder » Oct 05, 2011 7:15 pm

Unruh effect sez there r moar particles in an accelerating frame than an intertial 1. ani fewtewer big rip onli rips a bag to initiate teh next aeon, an on...
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Re: Noble Prize for Dark Energy trio

#5  Postby Dudely » Oct 05, 2011 7:24 pm

tuco wrote:So, if everything is getting further apart then new matter is being created, new bread?


Huh? No. . .

You're not making more bread when it rises, you're just watching yeast convert sugar into carbon dioxide.
You're not making more matter when the universe expands, you're just watching all the current matter move further apart. Consider the raisins analogous to galaxies or particles- it makes no difference.


As a side note you can make matter all you like, you just have to lock up energy to do it. Conversely you can destroy it but you release a proportional amount of energy when you do so. That implies if the expansion were to create 'new' matter it would actually be creating energy. And as we all learned in science class creating energy is impossible.
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Re: Nobel Prize for Dark Energy trio

#6  Postby tuco » Oct 05, 2011 7:38 pm

So .. I am making bigger holes? What's in them? I don't like making matter without energy.
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Re: Nobel Prize for Dark Energy trio

#7  Postby Lion IRC » Oct 05, 2011 7:52 pm

One thing which is expanding is our knowledge about how LITTLE we know.

Everytime we make a new discovery it always seems to come with a realisation that "the horizon" is even further away than what we previously thought.

The primitive human who thought the universe was just a few miles from one end to the other or that you could build a "Tower of Babel" to reach God had a limited understanding of their own ignorance and short-sightedness.

How lucky are we? We get to glimpse "cosmic bruising" and faster than light particles, and dark energy. Our Towers of Babel, like SETI and CERN aim for that which is infinitely beyond us in light years and infinitely miniscule in space/time - yocto-seconds, atto-seconds.

Is there no limit to how much we have yet to learn about how little we know?
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Re: Nobel Prize for Dark Energy trio

#8  Postby Calilasseia » Oct 05, 2011 8:18 pm

The expansion of the universe isn't due to motion of its constituents. It's due to the fact that the fabric of space-time itself is expanding. If you want an analogy, inflate a balloon to about 1/3rd of its fully inflated size, then draw little dots on it, representing galaxies. Then inflate the balloon some more. The "motion" of the dots isn't because they possess any intrinsic motion, it's because they're embedded in a metrical frame that is expanding. Space-time expansion is similar to this.

The fun part about space-time expansion is that it's happening even inside your body, and for that matter, the space between subatomic particles is also expanding. But on the everyday scale, the rate of expansion is so small, that it cannot even be measured. However, once you start to point telescopes at bodies that are millions of light years away, the expansion becomes measurable, courtesy of doppler shift of the received light. The Hubble Constant H0 is a measure of this spacetime expansion, and figures for H0 usually over around 70 Km s-1 Mpc-1. Convert that into SI units, and you end up with a lowly 2.3 x 10-18 (m/s) per metre. To put this into perspective, an atomic nucleus has a size (assuming a spherical mass distribution) of r0A1/3 (courtesy of Kaye & Laby) where r0 is a constant whose value is approximately 1.2 x 10-15, and A is the mass number of the nucleus in the Periodic Table - therefore a Hydrogen nucleus is around 1.2 x 10-15 metres across. It soon adds up though when you consider objects that are large distances apart - a galaxy that is 100 megaparsecs (3.09 x 1024 metres) away from us has a recession velocity of:

(2.3 x 10-18) x (3.09 x 1024) = 7.1 x 106 m/s or 7,100 Km/s

Calculating backwards, you can work out how far away an object has to be in order for its recession velocity to equal c - the requisite distance is 1.30 x 1026 metres, or 4.22 billion parsecs (13.8 billion light years) and 13.8 billion years is conveniently close, within the limits of experimental error, to the quoted value for the age of the observable universe.

This all leads to some interesting mental gymnastics, however, when you consider what's happening to you or I. Thanks to the expansion of space, if you or I stand still for a moment, and stick out our arms, then our fingertips are receding from each other (assuming for the moment that you and I both have a 2 metre arm spread) at 4.6 x 10-18 metres per second. Consequently, for our fingertips to end up 4 metres apart instead of 2, we will have to wait approximately 8.7 x 1017 years. I suspect the universe as a whole will have undergone some profound changes itself in that time, let alone you or I. :)
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Re: Noble Prize for Dark Energy trio

#9  Postby THWOTH » Oct 05, 2011 8:27 pm

Dudely wrote:It means that everything in the universe is getting further apart, relatively speaking. It's kind of like bread dough with raisins or something in it. As it sits on the counter to rise the raisins get further apart...

Now, I get this but, relatively speaking of course, are the raisins expanding, and their pips too?

Dudely wrote:Remember, you can't think about the universe in a normal three-dimensional way because it IS the normal three dimensions. Asking what it's expanding into, for example, is like asking what happens when you go south of the south pole.

The notion of what the universe is or might be expanding into is an interesting one, but in the sense of what the universe will become rather than in the sense of what volume it is occupying or inhabiting. However... :D

Saying that "everything in the universe is getting further apart" specifically seems to conjure the idea of a volume - for if thing-A and thing-B are getting further apart then the volume of the universe which encompasses both of them is also increasing. The conception of the universe being a thing which comprises and/or is occupying a bounded volume, like the dough ball etc., seems to come along with the discovery that the universe 'expands' I think.

Hmm. :think:
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Re: Nobel Prize for Dark Energy trio

#10  Postby Dudely » Oct 05, 2011 8:30 pm

tuco wrote:So .. I am making bigger holes? What's in them? I don't like making matter without energy.


Are you being facetious? Perhaps preying on an imperfect analogy?

The universe is expanding because for some crazy unknown reason it started expanding at the big bang. Gravity is slowing it down by. . . being gravity. At a certain density the matter in the universe should be enough to let gravity take over and collapse everything back again.

However, our observations of galaxies orbiting each other threw a bit of a kink in this. Given the mass contained in any given galaxy we can calculate how they should orbit another galaxy. We actually observe them orbiting as though they contained more mass- mass we didn't account for because we couldn't see it. The only explanation is there must be some kind of mass which interacts with virtually NOTHING. It doesn't reflect light, it doesn't bump into atoms- nothing. This is what we call dark matter. The problem is if we plug dark matter into the equation we get a universe too heavy to keep expanding. Our best observations indicate the expansion is speeding up, not slowing down. It's postulated, then, that there must be a dark energy which works on a universal scale to push everything apart.

Even though the universe is expanding we don't see the objects around us increase in size proportionally because gravity is still doing its thing keeping everything together. In billions of years nothing will have changed but the distance between the islands where gravity is strong enough to overcome the expansion- galaxies. As the expansion speeds up, however, so too does the amount of mass needed to have gravity overcome this and keep everything stuck together. Eventually, it will slowly rip galaxies apart. After that, it will pull on atoms themselves until it is stronger than the forces holding THOSE together and the universe becomes devoid of everything we consider matter. Because heat is a function of how fast atoms are wiggling around and because more space means more space to wiggle, and therefore less heat, this is referred to as "heat death".

So to explain the properties of space further:
"Space" describes an aspect of the universe just as "south" describes an aspect of movement in relation to a finite sphere (or any other object, really). They are both descriptions or labels of properties. They are a way for our mind to make sense of what's around us and hierarchically sort things out. Passing beyond or outside the subject makes the description of that aspect invalid. There is nothing south of the south pole because south describes how to move about the earth. Leaving the earth makes that description invalid because you're not dealing with something that contains that property as you understood it before. Passing outside of the universe is the same thing in regards to both space and time. They are descriptions of aspects which no longer apply.

It's not even that there is nothing there. It's not even "nothing". It's just. . . nothing. There is no proper word to describe it. It's not an empty existence, it's the lack of any existence at all.


All that being said . . .

The expansion of space is just a thing the universe is doing. We know what it is, we can look at it, and we can sort out what we think it's going to do as time goes on. It's not even that hard to understand once you know how it interacts with everything else.
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Re: Nobel Prize for Dark Energy trio

#11  Postby THWOTH » Oct 05, 2011 8:32 pm

Lion IRC wrote:One thing which is expanding is our knowledge about how LITTLE we know.

Everytime we make a new discovery it always seems to come with a realisation that "the horizon" is even further away than what we previously thought...

Then we need to discover more things more quickly, until we've gone all the way round.

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Re: Nobel Prize for Dark Energy trio

#12  Postby Dudely » Oct 05, 2011 8:37 pm

Calilasseia wrote:Thanks to the expansion of space, if you or I stand still for a moment, and stick out our arms, then our fingertips are receding from each other


Doesn't gravity stop this? Surely as the universe expands it does not cause Earth to occupy a greater volume?

Heck, even if this is true your arms would STILL be the same distance apart so far as you could tell. If everything expanded then so too would both your arms and the meter stick used to measure the distance between them.

It works as a thought experiment (more or less) but it wouldn't actually happen would it?
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Re: Nobel Prize for Dark Energy trio

#13  Postby tuco » Oct 05, 2011 8:59 pm

Facetious? Those are questions one gets when one starts to ask what the nature of space-time is. Nothing, but not that kind of dark energy, sounds good to me as it brings us back on topic - 2 < 0
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Re: Nobel Prize for Dark Energy trio

#14  Postby newolder » Oct 05, 2011 9:03 pm

Dudely wrote:
tuco wrote:So .. I am making bigger holes? What's in them? I don't like making matter without energy.


Are you being facetious? Perhaps preying on an imperfect analogy?

The universe is expanding because for some crazy unknown reason it started expanding at the big bang. Gravity is slowing it down by. . . being gravity. At a certain density the matter in the universe should be enough to let gravity take over and collapse everything back again.

isn't this primitive cyclic model what the prize winning entry disproves by repeated experiment? :ask:
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Re: Nobel Prize for Dark Energy trio

#15  Postby Dudely » Oct 06, 2011 11:57 am

newolder wrote:
Dudely wrote:
tuco wrote:So .. I am making bigger holes? What's in them? I don't like making matter without energy.


Are you being facetious? Perhaps preying on an imperfect analogy?

The universe is expanding because for some crazy unknown reason it started expanding at the big bang. Gravity is slowing it down by. . . being gravity. At a certain density the matter in the universe should be enough to let gravity take over and collapse everything back again.

isn't this primitive cyclic model what the prize winning entry disproves by repeated experiment? :ask:


I said "At a certain density the matter in the universe should be enough to let gravity take over and collapse everything back again." I did not say the density IS above that value, or that it ever would be. In fact- as I explain a few sentences later- it isn't. Precisely because we don't see the expansion slowing down we know this not to be the case. However, we have to add a bunch of crazy unproven variables into the mix to make all our observations jive with one another. This is what dark energy and dark matter is for.

If the density was above that critical value a collapse is what would happen. You can do the math yourself if you like- I did, so it cant be that hard :lol:. Of course, now we have to take into account all the dark stuff, but we really don't even know if that's the right answer yet.
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Re: Nobel Prize for Dark Energy trio

#16  Postby Dudely » Oct 06, 2011 12:04 pm

tuco wrote:Facetious? Those are questions one gets when one starts to ask what the nature of space-time is. Nothing, but not that kind of dark energy, sounds good to me as it brings us back on topic - 2 < 0


Ok, excuse me then. It's hard to tell online, especially when you have such a density of sarcasm as on this forum (I would have it no other way)!


You asked me about new matter being created when the universe expands and when I explained that isn't what would happen (and that it is, in fact, impossible), your response was to ask what was in the new space and that you didn't like making matter without energy. . . which is what I had just said wouldn't happen. That's why I thought you were being facetious.

Expanding space-time increase mass in the same way bread rising increases the number of raisins in the dough. It doesn't.
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Re: Nobel Prize for Dark Energy trio

#17  Postby Jumbo » Oct 06, 2011 12:22 pm

Dudely wrote:
Calilasseia wrote:Thanks to the expansion of space, if you or I stand still for a moment, and stick out our arms, then our fingertips are receding from each other


Doesn't gravity stop this? Surely as the universe expands it does not cause Earth to occupy a greater volume?

Heck, even if this is true your arms would STILL be the same distance apart so far as you could tell. If everything expanded then so too would both your arms and the meter stick used to measure the distance between them.

It works as a thought experiment (more or less) but it wouldn't actually happen would it?

In some sense the expansion and its acceleration is part of gravity. (The terms that drive the expansion are present in the General theory of Relativity which describes gravity). The scale of the effect is overwhelmed by things like the strong nuclear force, and the more conventional parts of gravity over smaller scales so galaxies and planets etc do not expand but the universe does. If the rate of the universe expanding becomes high enough though the effect may dominate even those things keeping the galaxies and planets together and the whole lot may be torn apart eventually.

The expansion of the universe is tricky to visualise because its not really a volume expanding into anything else which is what virtually all analogies imply. Its more a case of all of the bodies within the universe finding over time that the distances between them are increasing. The rate of increase getting faster over time.
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Re: Nobel Prize for Dark Energy trio

#18  Postby Dudely » Oct 06, 2011 12:28 pm

Jumbo wrote:
Dudely wrote:
Calilasseia wrote:Thanks to the expansion of space, if you or I stand still for a moment, and stick out our arms, then our fingertips are receding from each other


Doesn't gravity stop this? Surely as the universe expands it does not cause Earth to occupy a greater volume?

Heck, even if this is true your arms would STILL be the same distance apart so far as you could tell. If everything expanded then so too would both your arms and the meter stick used to measure the distance between them.

It works as a thought experiment (more or less) but it wouldn't actually happen would it?

In some sense the expansion and its acceleration is part of gravity. (The terms that drive the expansion are present in the General theory of Relativity which describes gravity). The scale of the effect is overwhelmed by things like the strong nuclear force, and the more conventional parts of gravity over smaller scales so galaxies and planets etc do not expand but the universe does. If the rate of the universe expanding becomes high enough though the effect may dominate even those things keeping the galaxies and planets together and the whole lot may be torn apart eventually.

The expansion of the universe is tricky to visualise because its not really a volume expanding into anything else which is what virtually all analogies imply. Its more a case of all of the bodies within the universe finding over time that the distances between them are increasing. The rate of increase getting faster over time.


I explained it that way in an earlier post so was wondering if my understanding was correct. Good to see that it is! Makes for less editing of previous posts ;)
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Re: Nobel Prize for Dark Energy trio

#19  Postby THWOTH » Oct 06, 2011 12:45 pm

Jumbo wrote:[...] The expansion of the universe is tricky to visualise because its not really a volume expanding into anything else which is what virtually all analogies imply...

This is my problem. I don't think there is any imagery available to properly illuminate what it actually means to say the universe to be expanding.

Jumbo wrote:Its more a case of all of the bodies within the universe finding over time that the distances between them are increasing. The rate of increase getting faster over time.

These are the dry facts of the matter, but I think the difficulty in conceiving of the universe as an expanding is that one generally plumps for the idea of a volume expanding or of a volume in which cosmological bodies are getting further apart. The issue is further confused by the fact that what we call the universe is actually the observable universe and may not even be the universe proper.
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Re: Nobel Prize for Dark Energy trio

#20  Postby Jumbo » Oct 06, 2011 12:55 pm

I explained it that way in an earlier post so was wondering if my understanding was correct. Good to see that it is! Makes for less editing of previous posts

I hadn't noticed that! It looks like we agree which is reassuring. Of course we could both be wrong but im sure if we are someone will point it out pretty soon.

This is my problem. I don't think there is any imagery available to properly illuminate what it actually means to say the universe to be expanding.

I know. This is the issue with lots of physics. There are plenty of analogies that sort of describe the situation but at the same time are misleading if examined in any detail. Our minds evolved to survive on this planet with little need in the past to contemplate such ideas as cosmology. I think one of the greatest challenges for anyone researching such things is to discard the preconceptions and imagery that has been accumulated over the years of experience of the more local world.

Yes what we often call the universe is just the bit that we see but its likely that the whole lot is following the same general pattern.
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