Cosmology

[BobHegwood]

Much appreciated here Good Doctor...

This is a fascinating thread.

Thanks all, Brain-Dead

[cartrite]

So no systematic searches for Dark Energy beforehand.

I am a little confused about the differences between Dark Matter and Dark Energy. I always thought that matter and energy were different manifestations of the same thing. I'll have to look into this subject more.
cartrite

[t00fri]

So no systematic searches for Dark Energy beforehand.

I am a little confused about the differences between Dark Matter and Dark Energy. I always thought that matter and energy were different manifestations of the same thing. I'll have to look into this subject more.
cartrite

From the microscopic perspective of Particle Physics, Dark Matter is associated with a certain kind of non-luminous massive particles (Neutralinos of Supersymmetry, Axions,...), while dark energy manifests itself as a force that provokes an accelerated expansion of the Universe AGAINST the deceleration that occurs due to the gravitational pull of the mass distribution in Space.

One day, a close dynamical connection between Dark Matter and Dark Energy may indeed emerge. Yet at the present incomplete level of understanding, the two are treated as separate components.

Bye Fridger

[cartrite]

From the microscopic perspective of Particle Physics, Dark Matter is associated with a certain kind of non-luminous massive particles (Neutralinos of Supersymmetry, Axions,...), while dark energy manifests itself as a force that provokes an accelerated expansion of the Universe AGAINST the deceleration that occurs due to the gravitational pull of the mass distribution in Space.

Well put. I can understand what your saying here, but ..........

I am a little confused about the differences between Dark Matter and Dark Energy.

what I have trouble understanding is that if a tiny amount of dark matter would equal a very large amount of dark energy, why would this even be questioned since there is supposed to be so much (90%) of dark matter.
In other words, If there is Dark Matter then there must be Dark Energy?
Unless of course DE!=DMC^2.
cartrite

[t00fri]

One of my deepest scientific principles is to always assume that there is something more out there that nobody knows anything about yet.

While such an attitude might seem promising at first, usually it is NOT. While it is always intellectually valuable to ask "piercing" questions, a thorough formation in this difficult field is inevitable for making real progress!

This has VERY little to do with understanding fancy mathematics, as you tend to put it. Math is just a "shortcut" of our physics language. Also clicking Websites won't help much and often may be misleading . What is really at stake is a grasp of the underlying physical picture and transparency of argumentation.

Firstly, there are many traps that require lots of theoretical physics Know How. A simple example: when you talk about the distance of galaxies in an expanding Universe, how do you define distances? That requires e.g. the knowledge of General Relativity in order not to talk nonsense...

But most importantly, one needs to KNOW the theoretical framework to filter the bad or accidental arguments from the promising ones. Physics is a huge puzzle that requires to see the WHOLE picture in order to have a chance for success!

Amateurs usually get hooked at an isolated argument that happens to appear attractive to them.

But it should not be forgotten that many bright scientists and a huge investment of money in clever experiments have set a reliable basis of knowledge that amateurs usually ignore...

Bye Fridger

[t00fri]

In other words, If there is Dark Matter then there must be Dark Energy?
Unless of course DE!=DMC^2.
cartrite

cartrite,

this famous equation does NOT mean that the amount of energy in the Universe has to equal the amount of matter!

It rather means that mass is a form of energy or under certain conditions can be converted to energy (and vice versa).

Bye Fridger

[Nick]

While I'm at it, here's another fun theory. Would anyone be able to explain to me why this couldn't POSSIBLY be the case:

Suppose there is a class of particles in the universe that has a similar sort of interaction to electromagnetic particles. (I believe what I'm thinking of is called "guage symmetry". Correct me if I'm wrong.) For these particles, however, the rules of interaction are exactly reversed: whereas in electromagnetics, like charges repel and opposite charges attract, suppose instead that in these hypothetical particles, like "charges" attract and opposites repel. This would cause particles of like "charge" to clump together, and oppositely charged clumps to push away from each other, all the while collecting and combining with other clumps of like charge. Ultimately, you would end up with large regions of space filled entirely with only one type of charge. Any particles of the opposite charge that were hypothetically placed inside such a region would quickly be expelled from it.

Now suppose inside one such region - let's say a region of "positive" matter - on one particular spherical clump of this matter, intelligent life emerged and began observing the universe around it. At least at first, these lifeforms would only be familiar with half of this interaction: all of the matter surrounding them, including that which made up their own forms, would be entirely of the "possitive" type. The nearest sizable coagulation of "negative" charge would be, say, several thousand lightyears away. The lifeforms would naturally assume at first that there only was one kind of charge involved in this particular force.

Now lets give this hypothetical type of "charge" some sort of name. How about "mass"? Yeah, mass would be a good name for it.

There is much I don't understand about current observations of the universe and the mathematics of current theory, but what I've just proposed fits verrrry nicely with everything I do understand.

If no other force of the universe ever overtook this one at any scale, this force would ultimately cause ALL the matter of "positive" mass and ALL the matter of "negative" mass to coagulate into exactly two regions of opposite masses. This would effectively divide the entire universe into two universes (universi?), whose main interaction between each other would simply be to push further apart. However, if instead there was a certain scale at which other forces began to dominate the movement of matter, the result would be a rough limit to the size of these coagulations. Instead of resulting in exactly two sub-universes, this force would instead result in a scattering of "island universes"...anyone heard that term before?

I believe this could help explain the spiral nature of galaxies as a result of the seperation process of the two types of mass. It could explain why the outer regions of galaxies rotate faster than "positive mass" alone could account for. It could help explain why something between the galaxies seems to be pushing them apart. What's more, I expect relativity theory could quite easily be modified to include both types of mass and the "antigravity" produced between them.

If we assumed that "positive mass matter" and "negative mass matter" was identicle in every way, then we would expect identicle types of coagulation structures from each type. I.e: "negative mass" galaxies should be expected to be identicle in structure and distribution to "positive mass" galaxies. Observing our "positive mass" galaxies, however, makes it clear that this cannot be the case. This suggests that the most common "negative mass" matter is different in several ways from our "positive mass" matter. This would not be unexpected, however. After all, protons and electrons, the primary particles by which electromagnetism makes its effects known, are different in almost every respect, excepting only the magnitude of their electromagnetic charge.

Is that not beautiful? If I turn out to be a genius, I hold all of you witness that I thought this stuff up completely independently.

[t00fri]

This is now really for another forum ("alternative" physics or whatever these are called)

Selden?

Bye Fridger

[cartrite]

In other words, If there is Dark Matter then there must be Dark Energy?
Unless of course DE!=DMC^2.
cartrite

cartrite,

this famous equation does NOT mean that the amount of energy in the Universe has to equal the amount of matter!

TRUE. But what I thought is that with so much Dark Matter around some of it must have been converted to energy. And if we are "looking" for Dark Matter ........why not also look for Dark Energy. Unless the two have nothing to do with each other.
cartrite

[t00fri]

In other words, If there is Dark Matter then there must be Dark Energy?
Unless of course DE!=DMC^2.
cartrite

cartrite,

this famous equation does NOT mean that the amount of energy in the Universe has to equal the amount of matter!

TRUE. But what I thought is that with so much Dark Matter around some of it must have been converted to energy. And if we are "looking" for Dark Matter ........why not also look for Dark Energy. Unless the two have nothing to do with each other.
cartrite

Certainly, the search for Dark Energy has been and still is ongoing VERY intensively. We know meanwhile that 70% of the Universe's energy fraction is in form of Dark Energy (Omega_Lambda=0.7)! There is NO doubt about this. The matter fraction (Omega_matter) is very small in comparison. Since the WMAP experiment about the Cosmic Microwave background radiation, we have very precise data about these quantities.

Knowing about the evolution in time of these different components since the Big Bang within GR, what is most mysterious is WHY at our present time these ratios are what they are! We usually call this problem by the slogan "Why Now?".

Bye Fridger

[Nick]

This is now really for another forum ("alternative" physics or whatever these are called)

Selden?

Bye Fridger

I'm afraid I don't understand you. Or rather, I'm afraid you don't understand me.

My purpose here is not to argue for alternative theories as much as it is to argue against the current popular ones. More accurately, I am trying to have a dialog about why current theories are so popular (although that dialog is clearly not happening here). My "crazy theories" as you would probably label them are more presented as arguments. Look at these theories, and explain to me why they are impossible. I do not think inflationary cosmology is the religion of close-minded conformist zealots, or anything like that. However, I do believe that, if it is indeed the correct model, anyone who is really familiar with it should be able to able to refute any alternative theories effortlessly - not just bad theories, but good ones too (I flatter myself my theories fall into the second category).

Consider the presentation of my alternative theories a challenge, as part of a philosophical discussion entirely relevant to all areas of physics and astronomy.

[Cham]

Consider the presentation of my alternative theories a challenge, as part of a philosophical discussion entirely relevant to all areas of physics and astronomy.

The problem with this, here, is it will most probably "diffuse" in various OFF topic subjects and degrades. According to the topic's title : "cosmology", we should talk about what we currently think we know about our expanding universe. Or isn't ?

[Nick]

Thats a very good point, and I'm thinking in the same general direction. I've already started what I hope will be a more fruitful discussion (for my personal purposes) at the Bad Astronomy forum as Selden originally suggested (I go by TheNick there, if anyone is interested).

[BobHegwood]

Since dark matter or dark energy does not radiate at any detectable wavelength, only it's effect can be seen. So is it really there or is this a patch for all our current theories?
cartrite

This is an extremely interesting question, but let's apply it another
way too. Gravity - as far as *I* know - does not radiate at any
detectable wavelength either does it? I mean, we can obviously
observe it's effects, but how does one measure gravity other than by
observing the amount of mass involved in the selected object? It's
effects are the only determining factor are they not?

Please keep in mind that I have absolutely NO education here, but am
still very much intrigued by this topic. It seems to me that you're
saying the same thing with regard to gravity here...
i.e. - Is gravity really there or not?

PS - If you would prefer that I just keep my mouth shut, please
just tell me. No problem at this end if that's the case. It's just
that - again - I'm facinated by this topic.

Thanks, Brain-Dead

[cartrite]

Gravity - as far as *I* know - does not radiate at any
detectable wavelength either does it?

Did you ever hear of gravitational radiation? I think there are some experiments that try to detect gravitational waves.

Is gravity really there or not?

No I'm not saying that at all. I was trying to point out that we don't really know what is causing stars at the outer edge of the galaxy to orbit as fast as they do. The gravity theory doesn't explain the speed they are moving unless you add more mass to the system. We can not detect this "extra" mass at any wavelength so it is called Dark Matter or "Missing Matter". What I was trying to say is maybe there is no extra matter and there is some other unknown force causing this or we got the theory of gravity wrong for large complex galactic systems.

cartrite

[BobHegwood]

Did you ever hear of gravitational radiation? I think there are some experiments that try to detect gravitational waves.

No ia haven't, but that's generally a given with me.
You can rest assured that I'll be having a look though.

Is gravity really there or not?

No I'm not saying that at all. I was trying to point out that we don't really know what is causing stars at the outer edge of the galaxy to orbit as fast as they do. The gravity theory doesn't explain the speed they are moving unless you add more mass to the system. We can not detect this "extra" mass at any wavelength so it is called Dark Matter or "Missing Matter". What I was trying to say is maybe there is no extra matter and there is some other unknown force causing this or we got the theory of gravity wrong for large complex galactic systems.

cartrite

Well I understand that answer at least, and I appreciate very
much your taking the time to explain it to me. Still good stuff
here. I really do enjoy these explanations, so thanks again.

Take care, Brain-Dead

[cartrite]

No ia haven't, but that's generally a given with me. Wink
You can rest assured that I'll be having a look though.

Bob,
I just plugged "gravitational waves" into google and came up with this quickie
http://imagine.gsfc.nasa.gov/docs/featu ... waves.html
cartrite

[BobHegwood]

No ia haven't, but that's generally a given with me. Wink
You can rest assured that I'll be having a look though.

Bob,
I just plugged "gravitational waves" into google and came up with this quickie
http://imagine.gsfc.nasa.gov/docs/featu ... waves.html
cartrite

Yes, I have visited that site now too. Very interesting...

Gravitational waves and interferometry to measure same. Can't wait
to see the outcome of that research. It makes me wonder though.
Isn't this merely a way to measure the "effect" so to speak? In other
words, when the spacecraft actually record gravity waves as
determined by distance fluctuations between the satellites,
aren't they still just seeing the "effects" of gravity and not the
"stuff" of it for lack of better words?

At any rate, still much appreciated by the Brain-Dead and
thanks again for the information. Good stuff!

[Fenerit]

As authority in matter, can I ask to you, Fridger, what do you think about the M.O.N.D. theory and about the Dirac's suggestion concerning the variation in time of the gravitational constant? I find these ipotheses very interesting as alternatives to the "dark" questions which seems to me to grant science of "misticism" and "mistery" and to play down what would be the scientific enterprise. My irony about dark matter and dark energy is the irony of who see in these paradigmatic forms the old ones, as the phantomatic "ether's wind" which was supposed "carry away" the electromagnetic field as now the dark energy is suppose, in similar sense, "carry away" the expansion of the universe. Yet for the ether were lot of evidence. Hope the thread go ahead.

[cartrite]

t makes me wonder though.
Isn't this merely a way to measure the "effect" so to speak? In other
words, when the spacecraft actually record gravity waves as
determined by distance fluctuations between the satellites,
aren't they still just seeing the "effects" of gravity and not the
"stuff" of it for lack of better words?

Personally, I would like to see the results of this. It would be interesting to have this experiment running while a star, perhaps at the distance of the crab nebulae or closer, go supernova. What would really be interesting is to have LISA detect "strong"gravity waves for say a month or so and then bam, a supernova lights up the sky. It would probably detect these waves soon after or at the same time. Or maybe not at all. Who knows.
cartrite