Explanation for Dark Energy

[Chris Peterson]

I put it to someone on here before I'm sure that dark matter/energy was a simple thing.

There is no such thing as "dark matter/energy".

[Chris Peterson]

reading topics like this, I can't help but imagine what would aliens think reading our "papers published in relevant peer-reviewed scientific journals"

I think they would recognize a culture that is becoming scientifically mature (sadly, not mature in other ways, however), that had identified most of the fundamental concepts underlying the Universe, and was well on its way to describing them.

[wonderboy]

I put it to someone on here before I'm sure that dark matter/energy was a simple thing.

There is no such thing as "dark matter/energy".

I was always under the impression that dark matter and dark energy were the same thing, it just depended on who you spoke to. Perhaps you could explain the difference (as best you can) so I can understand it, because I really wanna know so i don't make a fool of myself again. If you don't want to I understand.

Thank you.

[bystander]

try these

http://en.wikipedia.org/wiki/Dark_matter
http://en.wikipedia.org/wiki/Dark_energy

[Chris Peterson]

I was always under the impression that dark matter and dark energy were the same thing, it just depended on who you spoke to. Perhaps you could explain the difference (as best you can) so I can understand it, because I really wanna know so i don't make a fool of myself again. If you don't want to I understand.

You are certainly not making a fool of yourself... the misunderstanding is very common. No doubt it stems from the rather unfortunate choice of terms used for each of these things. However, they are entirely different.

Dark matter is just that- matter. It probably consists of non-baryonic particles, which don't interact with with electromagnetic forces and are therefore largely invisible. However, because the particles have mass they have gravitational effects, which makes that the primary (but not only) way we observe them. While the particles involved remain hypothetical and uncertain at this point, non-baryonic matter is not hypothetical, and has been directly observed (e.g. neutrinos). The effects of dark matter are observed over local areas- galaxy clusters and smaller.

Dark energy is the name given to a property of space that is responsible for the apparent acceleration of universal expansion with distance. Although it is generally treated as a form of energy, it is very unclear just what it actually is- different theories treat it quite differently. Although the phenomenon of accelerated expansion is pretty well supported by observation, the underlying theory is much less developed. The effects of dark energy are observed over the Universe as a whole, and not seen in any sort of local measurements.

[RJN]

Dark matter, like regular matter, dilutes as the universe expands. Conversely, and quite oddly, dark energy does NOT dilute as the universe expands. Dark energy's density is theorized to have always been the same. A goal of modern observational cosmological research is to check the validity of this conjecture.

[wonderboy]

It was dark energy that I was on about in my previous post. I think RJN was the person who rubbished my theory that dark energy is the by product of gravity. As gravity pulls things in, so dark energy pushes things out.

Thanks for the links bystander

[makc]

I think they would recognize a culture that is becoming scientifically mature (sadly, not mature in other ways, however), that had identified most of the fundamental concepts underlying the Universe, and was well on its way to describing them.

I see you believe humans are one step from becoming gods. But what if we're still just smartest apes? What if there's much more to logic, math, physics and everything?

[Chris Peterson]

I see you believe humans are one step from becoming gods. But what if we're still just smartest apes? What if there's much more to logic, math, physics and everything?

It is a big step from having a basic understanding of the underlying laws of the Universe and becoming gods!

I simply think that most of the physics we now know will turn out to be substantively correct. There are a few key areas that need to be filled in, but I don't think there will be many great surprises. The tool of science, honed over the last couple hundred years, has resulted in the acquisition of knowledge about nature becoming largely evolutionary. I don't know that we'll see revolutionary change again.

[neufer]

I simply think that most of the physics we now know will turn out to be substantively correct.
There are a few key areas that need to be filled in, but I don't think there will be many great surprises..

• Let us honor the forces of unification
  Believing in things as nu oscillation
  And mourn not the monojet that couldn't be deader
  For Carlo is coming with something much better.
  The seventh WOGU we have held in Toyama
  While waiting for word of the death of all matta.
  We must pity the student in his deep dark hole
  Whose thesis depends on that one monopole,
  Or on solar neutrinos that wriggle about
  Unless they are saying our sun has gone out.
  Some of us wonder how all things came to be
  Leaving nary a clue but for old gravity,
  And just seventeen particles, some of them quarks.
  Maybe seventeen more and some of them squarks.
  Something happened, they say, out in Cygnus the Swan,
  Don't bother to look 'cause now it's all gone.
  The Universe from Harvard looks like suds in the sink,
  So crash your computers and take time to think.
  The theory of everything, if you dare to be bold,
  Might be something more than a string orbifold.
  While some of your leaders have got old and scleotic,
  Not to be trusted alone with things heterotic,
  Please heed our advice that you too are not smitten -
  The book is not finished, the last word is not Witten.
  
  - Sheldon Glashow

[Astronut]

It would seem to me that Dark Energy and Dark Matter go together just as Grey Energy and Grey Matter do and White energy and White matter do and Clear energy and Clear Matter do.

Thats simple enought, right?
So it would follow that if you are going to have a conversation about a particular energy, or a particular type of matter, then you would also more or less include its partner also.

But then, what do i know? I do not even have a telescope!

[harry]

G'day

Bystander said

try these

http://en.wikipedia.org/wiki/Dark_matter
http://en.wikipedia.org/wiki/Dark_energy

They are well written and yet we still talk around the subject in theory.

If one could isolate dark matter and dark energy.

Which part would be in the formation of jets?

[Chris Peterson]

If one could isolate dark matter and dark energy.
Which part would be in the formation of jets?

None. Jets are simple byproducts of some spinning masses. They provide a mechanism for accretion discs to shed angular momentum, and in some cases they may redistribute material that eventually forms new stars, or perturb existing material and begin star formation. But they are fundamentally unimportant in terms of cosmology or the Universe. Your obsession with them doesn't change that.

[dougettinger]

Very cold objects are rather black in the infrared.* Likely the material is of a type that has to be very cold in order to remain collected by the objects that hold it. That almost also assures one that they would have to be very far from a star.

I really don't see the point you are trying to make. Sometimes you are talking about matter around stars (like the Oort cloud), and other times matter around galaxies (the mass responsible for explaining galactic rotation curves). These are different things.

Cold objects don't produce much IR. But ordinary baryonic matter interacts with electromagnetic radiation. If you put it around a galaxy, it will absorb short wavelength energy from that galaxy, heat up, and radiate IR. We should be able to observe that. Since we don't, it is a strong argument that dark matter is not baryonic. If you're suggesting some sort of exotic baryonic matter that doesn't heat up when exposed to EM... well, that's a lot less tenable than simple non-baryonic matter, which we already know exists and which has a well understood lack of interaction with EM.

My understanding is, the only way they are now having assurance about the Oort cloud existing is the required trajectory of objects that get knocked out and start falling toward the sun. Actually observation of it is lacking also. At most they may have spotted an object or two beyond Pluto. Kepler belt, as I understand it.

What does the Oort cloud have to do with this? Are you suggesting that material like that in the Oort cloud could be unidentified mass? Well, it is already accepted that there is cold baryonic matter that isn't luminous enough to detect. Its existence is allowed for in the ordinary matter part of the Universe's
energy budget. But it's nowhere near sufficient to explain all the missing mass. Consider the Oort cloud- the reason we can't observe it is because it's so diffuse- a mass of just a few Earth's (a tiny fraction of the entire Solar System) distributed in a cloud vastly larger than the Solar System. It's too diffuse to see its IR glow, and it's too low mass to have a measurable impact on the orbits of planets. This is very different than the sort of missing mass that must exist around galaxies. If there was enough mass in the Oort cloud to affect planetary orbits, it would have a very obvious IR signature.

A good question is brought forward. And, of course,this question has nothing to do with DE or DM. How do we know the Oort Cloud does exist other than postulate its existence because a source for comets is needed ?

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

How do we know the Oort Cloud does exist other than postulate its existence because a source for comets is needed?

It is hypothetical. But the need for a cometary source, the observed orbits of some comets, the observed orbits of a handful of KBOs, and some well regarded models provide enough evidence for its existence that most astronomers consider its existence pretty certain.

[dougettinger]

How do we know the Oort Cloud does exist other than postulate its existence because a source for comets is needed?

It is hypothetical. But the need for a cometary source, the observed orbits of some comets, the observed orbits of a handful of KBOs, and some well regarded models provide enough evidence for its existence that most astronomers consider its existence pretty certain.

I realize there are no models, but could not the hypothetical source be as well the formation and condensation of recent dense intermolecular clouds (DMCs) in interstellar space?

[Chris Peterson]

I realize there are no models, but could not the hypothetical source be as well the formation and condensation of recent dense intermolecular clouds (DMCs) in interstellar space?

I think if that were the case you'd expect rocky material as well as icy material. Out of tens of thousands of specimens, not a single meteorite has been found that doesn't date to the age of the Solar System. And all comets seem to share an ice/gas composition consistent with icy bodies that almost certainly formed with the Solar System. So while your idea may be a possibility, I don't know of any evidence supporting it, and there is plenty of evidence arguing for the Oort cloud being a remnant of the formation of the Solar System.

(From the standpoint of orbital dynamics, I don't see why recent condensates would concentrate in a halo around the Solar System.)

[dougettinger]

I realize there are no models, but could not the hypothetical source be as well the formation and condensation of recent dense intermolecular clouds (DMCs) in interstellar space?

I think if that were the case you'd expect rocky material as well as icy material. Out of tens of thousands of specimens, not a single meteorite has been found that doesn't date to the age of the Solar System. And all comets seem to share an ice/gas composition consistent with icy bodies that almost certainly formed with the Solar System. So while your idea may be a possibility, I don't know of any evidence supporting it, and there is plenty of evidence arguing for the Oort cloud being a remnant of the formation of the Solar System.

(From the standpoint of orbital dynamics, I don't see why recent condensates would concentrate in a halo around the Solar System.)

The majority of asteroids and their brethren, the meteorites, could well be collisional artifacts from the early solar system as well as the mid to late solar system and are not items captured from interstellar space. But the Kuiper Belt planetoids, perhaps like Pluto and Triton, certainly have rocky interiors. I am suggesting many of the comets as well as Kuiper Belt planetoids could have been captured from interstellar space intermittently as the solar system rides along in its orbit around the galaxy. These interstellar captured planetoids (ICP's) would then assume outer orbits, various elliptical orbits crossing other orbits, be captured by the outer planets, or occasionally collide with some pristine body in the solar system. I do not need to invent an Oort Cloud and a star passing nearby to provide perturbations.

Some data from studying the compositions of comets reveals very recent ages which would not allow for them to be remnants of the early solar system.

If you can undermine my line of reasoning, I would appreciate the enlightenment. (?) I will not take offense. I take immense pleasure in discussing these matters with the forum. Thank you.

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

The majority of asteroids and their brethren, the meteorites, could well be collisional artifacts from the early solar system as well as the mid to late solar system and are not items captured from interstellar space. But the Kuiper Belt planetoids, perhaps like Pluto and Triton, certainly have rocky interiors. I am suggesting many of the comets as well as Kuiper Belt planetoids could have been captured from interstellar space intermittently as the solar system rides along in its orbit around the galaxy. These interstellar captured planetoids (ICP's) would then assume outer orbits, various elliptical orbits crossing other orbits, be captured by the outer planets, or occasionally collide with some pristine body in the solar system. I do not need to invent an Oort Cloud and a star passing nearby to provide perturbations.

You still need an Oort cloud. In order to explain the frequency of long period comets, there has to be a lot of material out there. So all your explanation seems to do is shift the origin of the Oort cloud from the creation of the Solar System (when we are pretty certain there was plenty of condensed material available, and for which models support the formation of the cloud) to some vast quantity of debris picked up since then- which contradicts the observation that there doesn't seem to be much condensed material in interstellar space, and can't be explained by any straightforward orbital dynamics.

Some data from studying the compositions of comets reveals very recent ages which would not allow for them to be remnants of the early solar system.

That's not really true. The limited data suggests that some of these bodies have fairly new surfaces on them. There is no evidence I'm aware of that would suggest that the cometary material itself is newer than the Solar System.

[dougettinger]

The majority of asteroids and their brethren, the meteorites, could well be collisional artifacts from the early solar system as well as the mid to late solar system and are not items captured from interstellar space. But the Kuiper Belt planetoids, perhaps like Pluto and Triton, certainly have rocky interiors. I am suggesting many of the comets as well as Kuiper Belt planetoids could have been captured from interstellar space intermittently as the solar system rides along in its orbit around the galaxy. These interstellar captured planetoids (ICP's) would then assume outer orbits, various elliptical orbits crossing other orbits, be captured by the outer planets, or occasionally collide with some pristine body in the solar system. I do not need to invent an Oort Cloud and a star passing nearby to provide perturbations.

You still need an Oort cloud. In order to explain the frequency of long period comets, there has to be a lot of material out there. So all your explanation seems to do is shift the origin of the Oort cloud from the creation of the Solar System (when we are pretty certain there was plenty of condensed material available, and for which models support the formation of the cloud) to some vast quantity of debris picked up since then- which contradicts the observation that there doesn't seem to be much condensed material in interstellar space, and can't be explained by any straightforward orbital dynamics."

Can astronomers actually observe dark condensed matter between the edge of the solar system and adjacent stars 4 or more light years away ? Or are you saying there is no hypothesis for reasoning cold, dark matter between the stars?

Some data from studying the compositions of comets reveals very recent ages which would not allow for them to be remnants of the early solar system.

That's not really true. The limited data suggests that some of these bodies have fairly new surfaces on them. There is no evidence I'm aware of that would suggest that the cometary material itself is newer than the Solar System.

I am not sure what the difference is between fairly new surfaces or new compositions of comets?

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

I am not sure what the difference is between fairly new surfaces or new compositions of comets?

It means that the surface has been modified in some way- new material deposited, old material weathered or modified by radiation or solar wind. There is nothing in the measurements made of cometary material that remotely suggests it came from anywhere other than the formation of our own solar system.

[dougettinger]

Then I am not sure what the new revelation is. Any comet has its surface eroded by the solar winds as it orbits the sun.

doug ettinger

[dougettinger]

The majority of asteroids and their brethren, the meteorites, could well be collisional artifacts from the early solar system as well as the mid to late solar system and are not items captured from interstellar space. But the Kuiper Belt planetoids, perhaps like Pluto and Triton, certainly have rocky interiors. I am suggesting many of the comets as well as Kuiper Belt planetoids could have been captured from interstellar space intermittently as the solar system rides along in its orbit around the galaxy. These interstellar captured planetoids (ICP's) would then assume outer orbits, various elliptical orbits crossing other orbits, be captured by the outer planets, or occasionally collide with some pristine body in the solar system. I do not need to invent an Oort Cloud and a star passing nearby to provide perturbations.

You still need an Oort cloud. In order to explain the frequency of long period comets, there has to be a lot of material out there. So all your explanation seems to do is shift the origin of the Oort cloud from the creation of the Solar System (when we are pretty certain there was plenty of condensed material available, and for which models support the formation of the cloud) to some vast quantity of debris picked up since then- which contradicts the observation that there doesn't seem to be much condensed material in interstellar space, and can't be explained by any straightforward orbital dynamics."

Can astronomers actually observe the absence of dark condensed matter between the edge of the solar system and adjacent stars 4 or more light years away via infared techniques ? Or are you saying there is no hypothesis for reasoning cold, dark matter between the stars?

Or perhaps due to orbital dynamics the gravity field of the solar system cannot capture passing objects into elliptical orbits ?

Doug Ettinger
Pittsburgh, PA

[Chris Peterson]

Can astronomers actually observe the absence of dark condensed matter between the edge of the solar system and adjacent stars 4 or more light years away via infared techniques ?

I think that if it were dense enough for stars to collect halos of it massing several Earths, we would detect its EM emission. At interstellar temperatures, that would be in the radio spectrum, not the IR.

Or are you saying there is no hypothesis for reasoning cold, dark matter between the stars?

I assume that by "cold, dark matter" you mean cold, condensed (ordinary) matter. This was considered at one point as a candidate for dark matter, but that viewpoint has largely been abandoned, in part for the reason you suggest. There isn't a good theory for explaining such material in interstellar space without also requiring it much nearer to stars, where it should be easily detected.

Or perhaps due to orbital dynamics the gravity field of the solar system cannot capture passing objects into elliptical orbits ?

Yes, that's a problem as well. Escape velocity with respect to the Sun in the region of the Oort cloud is very low- not more than a few meters per second. Statistically, we are unlikely to encounter interstellar material with such a low velocity. Any comet we encounter that came from interstellar space should have a hyperbolic orbit with a high velocity. But we don't observe such comets. Any material in interstellar space that interacts with the Solar System will also find itself in a hyperbolic orbit, not trapped in a distant halo.