Galaxies In Dark Matter

[Guest jamongo]

I am trying to visualize "dark matter" as it pertains to our universe. The physicists seem to be getting closer and closer to making an announcement. Physicists running an experiment called DAMA, about 1,400 metres under Gran Sasso, a mountain near L’Aquila in central Italy, have claimed to have detected dark matter. Now, I just read that another group has said they had data suggesting the existence of "WIMPS". (http://www.economist.com/) So the best that I can visualize is a universe enmeshed in this dark matter the way M&Ms might be stranded throughout a big bowl of jello. Does this fly against reason, or do you think it is fairly close?

[Guest MacPhee]

I am trying to visualize "dark matter" as it pertains to our universe. The physicists seem to be getting closer and closer to making an announcement. Physicists running an experiment called DAMA, about 1,400 metres under Gran Sasso, a mountain near L’Aquila in central Italy, have claimed to have detected dark matter. Now, I just read that another group has said they had data suggesting the existence of "WIMPS". (http://www.economist.com/) So the best that I can visualize is a universe enmeshed in this dark matter the way M&Ms might be stranded throughout a big bowl of jello. Does this fly against reason, or do you think it is fairly close?

 

If "Dark Matter" really exists, shouldn't there be some close by? For example, inside our Solar System. After all, the Solar System is part of the Universe. So if the Universe contains Dark Matter, shouldn't there be some of it within our System? Then we could observe it in detail, and study its properties.

 

But Dark Matter seems to be too far away to study properly, and find out if it's really there. That's convenient for theorists, because they can't get proved wrong.

 

Doesn't that suggest, that the theorists have no idea what's going on, and have just made "Dark Matter" up?

[dduckwessel]

Something is holding everything together...they simply called the something, dark matter...afterall, it should have a name and dark matter is as good a fit as anything else!

 

I personally think that dark matter is a form of water (speaking of earth, this basic element of the universe filtered down into every living thing).

 

However, I've also heard dark matter described as sound waves or waves of sound (http://glafreniere.com/matter.htm) as I've read that dark matter pulsates (but I don't know if they mean pulsate as sound does!).

 

If it's a form of water, or as I think liquid sound it might explain why galaxies are in a constant twirling motion, as liquid motion produces certain common characteristics of movement. That's my amateurish view.

 

It's way above my head but could dark matter be sound waves (ripples/are producing the ever-expanding universe) produced from the original big bang (sound)?

[dduckwessel]

I agree with the M&M's in jello theory :)

 

Does the Doppler Effect show that dark matter could be a liquid (viscous) of some kind?

 

http://www.google.ca/imgres?q=the+doppler+effect&hl=en&biw=1024&bih=673&gbv=2&tbm=isch&tbnid=PAPHKokNA0dwYM:&imgrefurl=http://equalrightsforall.net/mechanical_waves/016_waves.htm&docid=iJsKlbiM-57AHM&imgurl=http://equalrightsforall.net/web%252520p20/doppler%252520shift2.gif&w=300&h=233&ei=vezgTveUDcrq0gHKpKzUBw&zoom=1

[Cyberia]

There are some theories which show no need for DM.

 

If it is claimed it exists, then why does no one have a clue as to what it is?

 

A superior Higg's boson maybe?

[JMJones0424]

In the interest of promoting a constructive discussion rather than unsupported fantasy

 

I personally think that dark matter is a form of water (speaking of earth, this basic element of the universe filtered down into every living thing).

Dark matter is not water. Water is baryonic matter. If dark matter were made of water, it would scatter and re-radiate em radiation and there would be no controversy necessitating dark matter to account for the missing mass in observed gravitational interactions of celestial bodies. Dark matter is matter that does not interact with other matter in any way other than gravitationally.

 

However, I've also heard dark matter described as sound waves or waves of sound (http://glafreniere.com/matter.htm) as I've read that dark matter pulsates (but I don't know if they mean pulsate as sound does!).

The link you provided deals with an alternative explanation of matter, not dark matter. It proposes that matter is made of waves, not sound waves, and its veracity appears questionable to me. This is not to say that it's incorrect, nor do I mean to imply that all alternative explanations are automatically invalid, but rather I recommend caution if you (like I) lack the background required to objectively evaluate alternative explanations.

 

... could dark matter be sound waves (ripples/are producing the ever-expanding universe) produced from the original big bang (sound)?

No. Sound is an oscillation of pressure through a medium. It is a mechanical wave. Dark matter is a concept invented to explain observed gravitational effects that require the existence of more mass than can be accounted for using evidence of other interactions with matter.

 

Does the Doppler Effect show that dark matter could be a liquid (viscous) of some kind?

 

No. When trying to measure dark matter, the doppler effect is one way to determine the rotational velocity of normal matter, then we approximate the mass required to maintain that rotation. Dark matter is the mass that is missing that is required to bring about the gravitational effects we observe.

 

For an easy overview of the subject, please see this blog:

http://scienceblogs.com/startswithabang/2011/10/the_status_of_dark_matter.php

 

 

There are some theories which show no need for DM. If it is claimed it exists, then why does no one have a clue as to what it is?

 

What theories are you referencing? Astronomers have a clue what dark matter is. The problem is that all we have to work with is indirect evidence. Dark matter is currently the best guess way to explain some observations.

[maddog]

I am trying to visualize "dark matter" as it pertains to our universe. The physicists seem to be getting closer and closer to making an announcement. Physicists running an experiment called DAMA, about 1,400 metres under Gran Sasso, a mountain near L’Aquila in central Italy, have claimed to have detected dark matter. Now, I just read that another group has said they had data suggesting the existence of "WIMPS". (http://www.economist.com/) So the best that I can visualize is a universe enmeshed in this dark matter the way M&Ms might be stranded throughout a big bowl of jello. Does this fly against reason, or do you think it is fairly close?

I have been contemplating what "dark matter" would look like as well. I have two scenarios and I have my personal preference of the two.

 

1. Dark Matter is something exotic that relates to the early universe and remains today somewhat non-interacting.

 

2. Dark Matter is pervasive throughout the universe and has internal processes though interacting with conventional matter on (so far) by way of gravity.

 

My personal preference is the latter though I have no evidence other than my intuition to conclude this.

 

We shall see once papers get published.

 

maddog

[maddog]

If "Dark Matter" really exists, shouldn't there be some close by? For example, inside our Solar System. After all, the Solar System is part of the Universe. So if the Universe contains Dark Matter, shouldn't there be some of it within our System? Then we could observe it in detail, and study its properties.

 

But Dark Matter seems to be too far away to study properly, and find out if it's really there. That's convenient for theorists, because they can't get proved wrong.

 

Doesn't that suggest, that the theorists have no idea what's going on, and have just made "Dark Matter" up?

 

Se my post #7 <-- this is what I mean by being "pervasive". To be this then - there is likely "some" dark matter on your shoe.

 

maddog

[maddog]

Dark matter is not water. Water is baryonic matter. If dark matter were made of water, it would scatter and re-radiate em radiation and there would be no controversy necessitating dark matter to account for the missing mass in observed gravitational interactions of celestial bodies. Dark matter is matter that does not interact with other matter in any way other than gravitationally.

For the most part I agree with you. Though I am not at this point willing to declare that "dark matter" or whatever it is -

is not baryonic in nature. True from what we know of the SM (Standard Model) Baryonic matter would have EM processes that

we could "see" this matter. This is not to say that other things are going on to prevent us from viewing these processes that we

currently are not a aware of. What we can say of "dark matter' is that gravity affects it and must therefore have some form of

mass. Much else and we are firing arrow at a target in the dark, blindfolded pointing in another direction.

 

Early on in the discovery of "dark matter" it was posited that maybe we need to consider that in the Halo of a galaxy are more "dead" brown dwarfs than we once thought. I have not seen this definitively shot down, just discouraged as no implicate reason this might be so.

 

... Astronomers have a clue what dark matter is. The problem is that all we have to work with is indirect evidence. Dark matter is currently the best guess way to explain some observations.

I was not aware of a specific "clue" other than its indirect affect by gravity as I alluded to earlier.

 

maddog

[dduckwessel]

Dark matter is not water. Water is baryonic matter. If dark matter were made of water, it would scatter and re-radiate em radiation and there would be no controversy necessitating dark matter to account for the missing mass in observed gravitational interactions of celestial bodies. Dark matter is matter that does not interact with other matter in any way other than gravitationally.

 

that's what I don't understand...if the universe is expanding it must have mass (of some kind!)? How can expansion happen if there isn't some kind of mass pushing it along?

 

I was thinking of water that had a greater mass, more like jelly...I can't find the link now but I read on one site that the planets were initially caught in a gravitational pull, which over time created a rut in dark matter (that keeps getting deeper and deeper) and it's not so much gravity but the rut that keeps the planets on their course...although way over my head I think the following may be alluding to this idea:

http://books.google.ca/books?id=TpMOAAAAIAAJ&pg=PA102&lpg=PA102&dq=planets+following+a+rut+orbit&source=bl&ots=S8VAkrZ9WW&sig=t-PgLmqa29Doa-hpELzsrmXe3n4&hl=en&sa=X&ei=UyX_TreoLsbMiQK12vC9DA&sqi=2&ved=0CCYQ6AEwAw#v=onepage&q=planets%20following%20a%20rut%20orbit&f=false

 

Regarding our moon, and others...why are they a certain distance from their host planet and then stop?...are all moons the same distance fromt their host planet or do the distances and spin vary from planet to planet?...did the moons slingshot or were they always that same distance from their host planet or were they closer at some point and gradually gained their present orbit (like a ball on the end of a long string being swung around very fast and so maintaining the same orbit)?

[JMJones0424]

I'm not the right person to be evaluating alternative ideas, however, the magazine you link to is from 1820, and seems to be describing the motion of the planets through aether, a concept which has been discredited and discarded from modern cosmology. You can find nearly every possible explanation for an observation online, the key is to be able to identify those that are likely to be valid and those that can be thrown out immediately. This is a skill that you develop over time, but you've got to start somewhere. One of the simplest ways of immediately judging the consensus view on a subject is to check wikipedia.

 

The observed accelerating expansion of the universe implies the existence of a force, not mass, causing the expansion. This force is called dark energy and should not be confused with dark matter, which is the mass required to hold together, gravitationally, various observed cosmic bodies like galaxies, galaxy clusters, etc.

 

I'm not sure I follow your questions about moons. No, there is no set distance from a moon and the planet it orbits. Earth's moon is not orbiting at a fixed distance, the distance from the Earth to the moon increases slowly over time, about 38 mm per year. . I don't think one can accurately make a blanket statement applying to all moons everywhere.

[CraigD]

that's what I don't understand...if the universe is expanding it must have mass (of some kind!)? How can expansion happen if there isn't some kind of mass pushing it along?

You’ve sort of have it backwards, dduck. Mass – that is to say the force all bodies with non-zero mass exert, gravity – doesn’t push, expanding a collection of bodies, but pulls, contracting it.

 

Expansion of such a collection can go on forever if the bodies have more kinetic energy – that is, are moving faster – than they have negative (don’t worry for now about the “negative” qualifier there – it’s just a technical correctness) gravitational potential energy – that is, the maximum energy gravity can store from the bodies getting further apart. If we call the collection “the universe”, we can call this condition “every body exceeding the escape velocity of the universe”. Cosmology has a special symbol to measure whether the real universe has this state, [imath]\Omega[/imath] (omega). If [imath]\Omega < 1[/imath], it does, and classical physics predicts it will expand forever, its expansion constantly slowing, but never enough to halt and reverse it. If [imath]\Omega > 1[/imath], it doesn’t, and the universe will eventually begin contracting, falling back into a “big crunch”, the opposite of a classical “big bang”.

 

There’s a dire problem with describing the universe using classical physics, though: no matter what the value [imath]\Omega[/imath], the expansion of the universe must be decreasing. Decades of observation and analysis lead present day astronomers and cosmologists to conclude that, inexplicably by classical theory, the expansion is actually increasing. When present day cosmologists use the term expansion, they’re usually talking about this, not the simple expansion described by classical physics.

 

It can still be put in classical terms, by just calculating the mechanical work necessary to explain the difference between theoretical prediction and observed reality, without attempting to explain its cause. This work (or, technical, the energy required to do it) is called dark energy. As with dark matter, “dark” here means essentially, “we can’t directly see it and am far from sure what it is or even if it ‘really’ exists”.

 

I was thinking of water that had a greater mass, more like jelly...

You seem to be confusing mass with density, or perhaps with viscosity. None have much to do with the motion of moons, planets, stars, and galaxies, however, because they move through near vacuum, not liquid.

 

I can't find the link now but I read on one site that the planets were initially caught in a gravitational pull, which over time created a rut in dark matter (that keeps getting deeper and deeper) and it's not so much gravity but the rut that keeps the planets on their course...although way over my head I think the following may be alluding to this idea:

http://books.google.ca/books?id=TpMOAAAAIAAJ&pg=PA102&lpg=PA102&dq=planets+following+a+rut+orbit&source=bl&ots=S8VAkrZ9WW&sig=t-PgLmqa29Doa-hpELzsrmXe3n4&hl=en&sa=X&ei=UyX_TreoLsbMiQK12vC9DA&sqi=2&ved=0CCYQ6AEwAw#v=onepage&q=planets%20following%20a%20rut%20orbit&f=false

The idea that the planets follow track, ruts, crystal spheres, or whatever, is an old, pre-scientific, one, discredited around the time that the idea that the sun and planets revolved around the Earth rather than the Sun was. Kepler spent a lot of time thinking about the idea (he was fond of the idea that the planets followed tracks determined by nesting the Platonic solids, know these days to gaming geeks as polydice), before concluding (reluctantly – he never really gave up on trying to find a more-or-less mystical geometric explanation) around 1609, that they don’t, and deriving his famous laws that almost perfectly describe how the planets and moons do move.

 

By the time the journal you reference was printed, in 1820, Newton’s theory of gravity was almost universally accepted. The article you reference, “Observations on the Phaenomena of the Universe. By A Newtonian”, doesn’t disagree with the theory, but debunks a theory by Richard Phillips that proposed that the planets float, like balloons, in a gas that surrounds the Sun. In short, it’s a debunking of a now obscure 19th century crank theory by a now obscure English (but prolific!) politician with a penchant for ranting about stuff he didn’t understand very well.

 

You seem to be casting around, dduck, for an intuitive grasp of astrophysics. I’m not sure how possible it is to have this, as being able to at least use (like Yours Truly, vs. derive, like Newton did) the classical formulae to calculate motion of gravity-interacting bodies is how most people develop and tune their intuition. I think the best course of study is just to start at the beginning and master the basics of classical physics. Otherwise, you’ll always have to take on faith the conclusions of people who do, or worse, of people who don’t, and worse still, won’t easily be able to tell one sort of person from another.

[dduckwessel]

You’ve sort of have it backwards, dduck. Mass – that is to say the force all bodies with non-zero mass exert, gravity – doesn’t push, expanding a collection of bodies, but pulls, contracting it.

 

Yes, I had it backwards. I was trying to make sense of dark matter as having 'flow' properties. Thank you for clarifying.

 

You seem to be casting around, dduck, for an intuitive grasp of astrophysics. I’m not sure how possible it is to have this, as being able to at least use (like Yours Truly, vs. derive, like Newton did) the classical formulae to calculate motion of gravity-interacting bodies is how most people develop and tune their intuition. I think the best course of study is just to start at the beginning and master the basics of classical physics. Otherwise, you’ll always have to take on faith the conclusions of people who do, or worse, of people who don’t, and worse still, won’t easily be able to tell one sort of person from another.

 

Yes, I was trying to 'fast-track' it or rather condense information. I will start at the beginning. Thank you :)

[sigurdV]

The observed accelerating expansion of the universe implies the existence of a force, not mass, causing the expansion. This force is called dark energy and should not be confused with dark matter, which is the mass required to hold together, gravitationally, various observed cosmic bodies like galaxies, galaxy clusters, etc.

 

At last!

 

Dark Energy enters into discussion... So why is not that force generated by our universe rotating?

[JMJones0424]

Because there is no evidence that the universe is rotating and that explanation does not explain the observed phenomenon.

 

EDIT: As usual, a flippant response is, on reflection, insufficient. Would you care to start a thread expounding on what leads you to think that universal rotation could explain dark energy, or what evidence you have that there is a universal rotation?

Edited January 12, 2012 by JMJones0424

[sigurdV]

I was asking WHY the dark force could not be considered an effect of rotation. I am under the impression that rotation causes a centrifugal force that increases with distance just like they tell me the dark force does. So at first sight rotation might explain the phenomen and could be taken as the first indication that the universe rotates. Therefore I would like to know HOW the possibility is ruled out. And: No, At first sight I dont think a new thread is necessary. Surely the matter is not THAT complicated?

 

PS On second thought: If there is no thread on Dark Energy then one should be constructed! Its no minor subject :)

 

PPS Done!

[JMJones0424]

As this thread is about dark matter, dark energy is indeed a different topic. I cannot fully answer your question. There are some recent studies that show there could be a slightly measurable rotation of the universe (for example http://arxiv.org/abs/1104.2815 ), but this is insufficient to explain dark energy. Centrifugal force is actually inversely proportional to distance. F=mv²/r .

 

A quick google search led me to this FAQ entry that places upper limits on the possible rate of rotation of the universe:

http://physics.stackexchange.com/questions/1048/what-if-the-universe-is-rotating-as-a-whole/12781#12781

 

I claim ignorance though, and would happily defer to someone else who could answer your question more effectively.