Re: Explanation for Dark Energy
Posted: Fri Apr 09, 2010 1:02 pm
There is no such thing as "dark matter/energy".wonderboy wrote:I put it to someone on here before I'm sure that dark matter/energy was a simple thing.
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There is no such thing as "dark matter/energy".wonderboy wrote:I put it to someone on here before I'm sure that dark matter/energy was a simple thing.
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.makc wrote:reading topics like this, I can't help but imagine what would aliens think reading our "papers published in relevant peer-reviewed scientific journals"
Chris Peterson wrote:There is no such thing as "dark matter/energy".wonderboy wrote:I put it to someone on here before I'm sure that dark matter/energy was a simple thing.
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.wonderboy wrote: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.
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 wrote: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.
It is a big step from having a basic understanding of the underlying laws of the Universe and becoming gods!makc wrote: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 wrote: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..
http://www.cithep.caltech.edu/macro/songs/glashow.html wrote:
- 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
They are well written and yet we still talk around the subject in theory.
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.harry wrote:If one could isolate dark matter and dark energy.
Which part would be in the formation of jets?
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 ?Chris Peterson wrote: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.gmellott wrote: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.
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.
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'sMy 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.
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.
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 wrote:How do we know the Oort Cloud does exist other than postulate its existence because a source for comets is needed?
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 wrote: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 wrote:How do we know the Oort Cloud does exist other than postulate its existence because a source for comets is needed?
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.dougettinger wrote: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?
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.Chris Peterson wrote: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.dougettinger wrote: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?
(From the standpoint of orbital dynamics, I don't see why recent condensates would concentrate in a halo around the Solar System.)
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.dougettinger wrote: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.
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.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.
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?Chris Peterson wrote: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."dougettinger wrote: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.
I am not sure what the difference is between fairly new surfaces or new compositions of comets?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.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.
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 wrote:I am not sure what the difference is between fairly new surfaces or new compositions of comets?
Chris Peterson wrote: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."dougettinger wrote: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.
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.dougettinger wrote: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 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 are you saying there is no hypothesis for reasoning cold, dark matter between the stars?
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.Or perhaps due to orbital dynamics the gravity field of the solar system cannot capture passing objects into elliptical orbits ?