Dark Matter

Originally posted by sasquatch672
Come on lad, I've read your posts, you're more educated than that. I don't imply that and I don't need to; furthermore, if I stated that, I would be as humble an emissary of that concept as there has ever been. As to your second question - this is a theory, not a law, because it doesn't fit the definition of a scientific law, but it's a pretty damn we ...[text shortened]... ake reasonable assumptions about it - among them, that the laws of physics apply to it.

Actually, we may have already 'seen' dark matter, albeit indirectly, through gravitational interactions with regular matter. See this link:
http://www.universetoday.com/2008/09/02/pushing-the-polite-boundaries-of-science-about-dark-matter/

Originally posted by FabianFnas
Do you imply that mass and energy is equivalent? Even that dark mass and dark energy is equivalent? Do we really know that much about dark mass and dark energy to make this asumption? I don't know...

Mass of the ordinary matter has a gravitational attraction. One thing I want to know is if dark matter has a gravitational repellation, and if this has to ...[text shortened]... ting expanition of the Universe? Or is it a fifth force of nature, besides the four well known?

Dark matter and dark energy are not the same thing. The notion of dark matter came about because galaxies have the wrong rotation speeds for the amount of visible matter. It´s called dark matter because telescopes, including radio telescopes, can´t see it. There are cosmological bounds on what types of matter the dark matter can be (hadronic, neutrinos etc.). There are various speculative theories about what it could be made of, including the lowest mass supersymmetric particles or other types of exotic matter.

Dark energy basically means what ever produces the cosmological constant. If you solve the Einstein field equations for a spherically symmetric space and include a positive cosmological term you get a solution known as de Sitter space which corresponds to a universe with an accelerating expansion. You can get the same effect from a matter sector with the right properties. The name dark energy is just a generic term for the physical mechanisms which generate the cosmological constant. There are a bunch of speculative particle physics based theories for what dark energy could be.

Dark energy seems to be making our universe expand. There are three forms and theories. In all of the equations that incorporate relativity, there is a value called "the equation of state" and it is represented by a small "w".

w = 1/3 = Electromagnetic radiation
w = 0 = Non-relavitistic matter
w = 1 = Relativistic matter
w = -1 = Cosmological Constant; aka vacuum energy
-1/3 > w > -1 = Quintessence: the value of w can change with time
w < -1 = Phantom energy.


The punch line when viewing w as a "final state of the universe" is as follows:

If w = -1 as per Einstein then the universe will continue to expand forever, and resolve itself into heat death. This has a lot going for it because the proposed results closely match OBSERVED cosmic background radiation measurments. The problem is that when calculations are done, this w predicts 10^120th power more vacuum energy than can be observed.

Quintessence implies that its density can change over time and from one location in the universe to another, making the "end of everything" difficult to predict. Think of this "something" being constant, exherting a force that may be diluted (like pouring red dye into a swimming pool as it is filled) or it may not dilute. Either is possible.

Phantom Energy (Robert Coldwell?) is an attempt at unifying Quantum reality to relativity in the form of "virtual particles" that comprise "empty space". In this theory the phantom energy driving all matter apart MAY be a perverse type of particle that relaxes by vibrating faster and faster.

The thing about states of w less then -1 is that they all end in the "big rip". The big rip means that all matter will be pulled apart into quarks(?) or some end particle. At the end of time, using phantom w:

At terminalRip(tRip) - 200 million years, Milkomeda destroyed
At tRip - 1 year Solar system unbound
At tRip - 1 hour Earth explodes
At tRip minus -1^-19 seconds atoms ionize
At tRip minus -10^22 seconds Nuclei and nucleons dissociate

Dark matter seems to be able to hold large structures like galaxies and galaxy clusters and superclusters together. Dark matter seems to be needed to counter the expansion attributed to dark energy, but they do not seem to have a link at this time.

btw... assuming w = -1.1 then expect the big rip in about 85 billion years. And may the force be with you, not at you.

Originally posted by DeepThought
Dark matter and dark energy are not the same thing. The notion of dark matter came about because galaxies have the wrong rotation speeds for the amount of visible matter. It´s called dark matter because telescopes, including radio telescopes, can´t see it. There are cosmological bounds on what types of matter the dark matter can be (hadronic, neutrinos ...[text shortened]... There are a bunch of speculative particle physics based theories for what dark energy could be.

Sorry if it was me leding this thread into dark energy, when the title of this thread is "Dark Matter".

Originally posted by sonhouse
Actually, we may have already 'seen' dark matter, albeit indirectly, through gravitational interactions with regular matter. See this link:
http://www.universetoday.com/2008/09/02/pushing-the-polite-boundaries-of-science-about-dark-matter/

That link is about as reliable as a clock in a brothel.

Originally posted by sasquatch672
Very superficial, not well thought-out - come on, you're capable of more than this as well.

My point is that describing a substance that is both invisible and
non-pervasive to radiation as 'matter' and 'energy' immediately
sends us on the wrong course for what to expect. What we are in
fact describing is the absence of mass and energy.

Regarding the space-time fabric you are seeking, you may be
interested to read that Ether is making a knockout comeback.
The idea is that Ether, being an all-pervasive field, behaves
in a similar way to Einsteins proposed 'elastic sheets'. The key
differences are that firstly it acts to 'soften' space rather than
'bend' it and secondly that it houses a threshold value for the
acceleration of a mass passing through it. Thereafter
it behaves in a different manner. A good analogue of this would
be the viscosity of air after an object breaks throught the sound
barrier.
The implications of this would mean that slower moving objects
on the outskirts of galaxies experience a greater mass.
The observation that is currently described by dark matter.
http://www.eurekalert.org/pub_releases/2006-08/ns-ert082306.php

With this in mind, I believe it is important when assigning labels
to universal constructs that we bear in mind, that we are in fact
labelling information.
When we speak of matter we are also speaking of energy which is
information. The same can be said of velocity, acceleration and
forces that we encounter.
The description of Ether above is for all intents and purposes, the
description of Mathematics. It is a description of how one substance
moves through another. It is information.

Why is it then such a leap of the imagination to consider that an increase
in the complexity of this information such as the addition of observers.
Or the loss of information by means of the cosmic horizon, black
holes etc . should be one of the "forces"/"masses"/"energies"/"fields" in our
universe today?

Originally posted by FabianFnas
Sorry if it was me leding this thread into dark energy, when the title of this thread is "Dark Matter".

Originally posted by sasquatch672 E=MC^2
This was the thing leading me into the equivalence between dark matter and dark energy.
He implied that E very well can be dark energy when M is dark matter.
A think you can very well bring energy out of dark matter, but this energy cannot be described as specifically dark energy.
Am I at the right track?

When dealing with dark matter, apply the Withnail principle: do not attempt anything without the gloves.

Originally posted by FabianFnas
Originally posted by sasquatch672 [b]E=MC^2
This was the thing leading me into the equivalence between dark matter and dark energy.
He implied that E very well can be dark energy when M is dark matter.
A think you can very well bring energy out of dark matter, but this energy cannot be described as specifically dark energy.
Am I at the right track?[/b]

Yes, you are on the right track. As a theory dark matter was thought of first - they hypothesized some invisible matter so dark matter is a logical name. It´s also nice from a marketing of science point of view. When they wanted a catch all name for the various types of theory that give an accelerated expansion they called it dark energy because dark matter already existed and they could jump on the dark science bandwagon. I assume the reason for using the word energy is because the matter sector appears in the Einstein Field equations as the energy-momentum density tensor.

I´ve got problems with the notion of dark matter - there´s some observations which contradicted the theory and so you decide that the observations are wrong and not the theory? Despite this there is some evidence (apart from galaxy rotation) that it exists (see the Wikipedia article for some links).

As a piece of science dark energy is fine, the observations agree with the basic prediction, and as this type of expansion is driven by the vacuum energy of scalar fields with non-zero vacuum expectations it´s something that is reasonable enough, as this exists in the standard model already. This doesn´t mean it´s right, on the basis of the Higgs vacuum you´d expect a cosmological constant about 80 orders of magnitude larger than the upper bound on the observed value.

Originally posted by Thequ1ck
That link is about as reliable as a clock in a brothel.

I dunno, I fixed plenty of 'em🙂