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ryanm
2009-Apr-24, 04:23 PM
Moved from http://www.bautforum.com/space-astronomy-questions-answers/87466-distance-between-planets-universes-expansion.html

This may be a bit off topic, but this is the closest thread I could find regarding what I was thinking.

I am still not sold on the whole "Dark Matter" concept or "Dark Energy". It seems like "We don't understand so lets make something up".

I am not a math major, so forgive my lack of data inclusion--there are far better than I on this forum.

I have some questions...

#1. Do we take the relative increase in mass due to velocity into account when estimating the overall mass of the universe? There is apparently 90%+ of the mass unaccounted for, but is this possibly due to relative velocity? How are we accounting for the invarient mass with so many different velocties in play?

#2. Are we able to account for all the differeing types of velocity that could affect the mass equation? For example, if the universe is expanding at 71Km/s, that is one factor to estimate. Then there is the rotation of that particular galaxy, followed by the rotation of the solar system, the orbit of the planets and finally the rotation of a planet.

To me, all of this "Relative Velocity" may need to be accounted for when trying to guesstimate the overall "Relativisitic mass" of the universe.

I understand that "relatively", two like objects moving in the same direction at the same speed are going to have "relatively", the same mass. However, if you take those objects and have them travel away from each other at the same speed, what happens to their relative mass?

#3. Again, another relativistic question--if an object approaching the speed of light, acheives a state of near infinite mass--is it possible we just have a few objects that are moving at an extreme speed that could account for this missing mass?

#4. If the two objects I mentioned earlier, were traveling at 3/4 the speed of light in opposite directions, would this not mean that the gravitational effect between these two objects would have to be traveling faster than light?

Forgive me if this has been asked before, I did a few searches but I didn't come up with anything that closely mirrors my questions.

I'm probably missing some key points of understanding in my questions.

Ken G
2009-Apr-24, 05:11 PM
It seems like "We don't understand so lets make something up". That is a rather general and complete description of the entire endeavor of science, I'm not clear where you are having a problem with it. Science always starts with observations that are not understood, and it composes the best models with the least added complications that can describe those observations, and then it looks for other observations that can be unified within that new model. If it finds them, it replaces the idea that we have "described" the observations with the idea that we now "understand" the observations. At every point, it is a process of "making things up", with the important caveat that what is made up is constantly subjected to testing and error-correcting. That's just exactly how science works, you are merely seeing it at an earlier stage than you are accustomed to, in regard to the observations that support "dark matter" and "dark energy".

#1. Do we take the relative increase in mass due to velocity into account when estimating the overall mass of the universe? Yes, all of relativity is included, including general relativity (it sounds like you may be thinking mostly in terms of special relativity, but that's not adequate for cosmology).
#2. Are we able to account for all the differeing types of velocity that could affect the mass equation? For example, if the universe is expanding at 71Km/s, that is one factor to estimate. Then there is the rotation of that particular galaxy, followed by the rotation of the solar system, the orbit of the planets and finally the rotation of a planet. Yup, all the motions that we observe are in there in principle, but most of the things on your list are quite unimportant compared to the simple mass of these things.


To me, all of this "Relative Velocity" may need to be accounted for when trying to guesstimate the overall "Relativisitic mass" of the universe.You have enough math skills to test that-- the correction to relativistic mass has a size that depends on the ratio of the velocities you mention, divided by c, all squared. Most of the things on your list are less than 300 km/s motions, so the correction is of size (300/300,000)^2 = one part in a million. So it's not of consequence.

#3. Again, another relativistic question--if an object approaching the speed of light, acheives a state of near infinite mass--is it possible we just have a few objects that are moving at an extreme speed that could account for this missing mass? Anything's possible, the question for science is, what is the most promising direction for forming new models. Science often gets that wrong, so all ideas need to be on the table, but "dark matter" seems a more promising avenue if we are going to postulate populations of matter that we have not yet observed. Still, all ideas should remain on the table.


#4. If the two objects I mentioned earlier, were traveling at 3/4 the speed of light in opposite directions, would this not mean that the gravitational effect between these two objects would have to be traveling faster than light?
No. Gravity requires general relativity, you can't just do special relativity with relativistic masses. But you can probably at least get somewhere by doing that, so if you do, you need to pick a reference frame to do the analysis. In the frame you mention, each mass is enhanced by a factor of 4/root(7) = 1.5 only. In the frame of either mass, the other mass is not moving > c, it is moving at 96% of c, (there's a different formula for adding speeds) and the mass enhancement will not be anything spectacular.

I'm probably missing some key points of understanding in my questions.You are really asking questions that require general relativity, and that's one of the harder areas of physics.

ryanm
2009-Apr-24, 05:54 PM
For lack of a better term, it just feels like we're missing something.

I know much of science is hypothesis and testing those ideas. In this case, dark matter and dark energy are proposed as possibilities for explaining things that at the present--we can't.

In the missing mass formulas, are we also taking thermodynamics into account? If dark matter is made up of neutrinos, how did the universe create such an incredible amount of them?

When we talk about the observation of gravitational lensing--how are we accounting for the incredible diversity of gravitational effects that could be involved in between our vantage point vs. what the actual state of the observed position?

If velocity by its nature, is an understanding of the "time" it takes for an object to travel between a known "relativsitic" distance, is it possible that we lack the proper understanding of the effect gravity has on time as a unit of measure at the observed location?

Maybe what we view as a constant for time for us greatly varies between galaxies as well as positions in the universe? If our understanding of time is incomplete in this respect, that would affect our understanding of the velocities we "perceive" in these galaxies which do not make sense given our mass estimations.

Ken G
2009-Apr-25, 03:41 AM
For lack of a better term, it just feels like we're missing something.We're always missing something, that's the nature of the beast. But I would say that many times in history, that feeling came when we were on the brink of a great discovery, but other times it came after we'd already had our great discovery and people were just having trouble letting go of some old way of thinking. Which is it this time? Who knows, time will tell.

I was once asked if I "believed in dark matter". The question took me aback for a moment-- what possible difference could it make whether or not I believed in it? As a scientist, I'm only qualified to answer if I think it is our current best model. That is much easier to answer in the affirmative.

In the missing mass formulas, are we also taking thermodynamics into account? If dark matter is made up of neutrinos, how did the universe create such an incredible amount of them? Good question, that's exactly why it is not widely thought that the dark matter is neutrinos. We think we have a good idea how many neutrinos there ought to be, and it isn't enough.


When we talk about the observation of gravitational lensing--how are we accounting for the incredible diversity of gravitational effects that could be involved in between our vantage point vs. what the actual state of the observed position? That's the job of astronomers, to bring to bear everything they can and try to think of all possibilities, and still come up with a best interpretation of what they are seeing. In that regard, history is dotted with stunning successes and less fortunate outcomes.


If velocity by its nature, is an understanding of the "time" it takes for an object to travel between a known "relativsitic" distance, is it possible that we lack the proper understanding of the effect gravity has on time as a unit of measure at the observed location? You are asking if our current best theory of gravity might be wrong. That is certainly possible, and is an active area being pursued. It often gets called "MOND"-- modifications to Newtonian gravity (you only need Newtonian gravity to understand the need for dark matter).


Maybe what we view as a constant for time for us greatly varies between galaxies as well as positions in the universe? If our understanding of time is incomplete in this respect, that would affect our understanding of the velocities we "perceive" in these galaxies which do not make sense given our mass estimations.Now you are getting at what science is all about, which is trying to find the simplest explanation, the least violent modification of what already works, in response to new phenomena. So all ideas need to be on the table, but the "current best model" will always be the simplest, the one that adds the least new and unconstrained phenomena. That's what Occam's razor really is, not the pop version you often hear (that the simplest explanation is "most likely to be right", if only that was generally true!). The lure of dark matter is that you can unify all these problems under one umbrella, you have one new kind of matter and poof everything (or many things) can be made to work out. If we instead follow the question you ask above, how complex will we need to make our theory of these "variations in time" to get everything to work out? Will that end up looking like the awkward cluge, instead of dark matter? Science has a constant need for fixing itself, but it must follow the dictum of seeking the "least awkward cluge".

DrRocket
2009-Apr-25, 03:55 AM
For lack of a better term, it just feels like we're missing something.

I know much of science is hypothesis and testing those ideas. In this case, dark matter and dark energy are proposed as possibilities for explaining things that at the present--we can't.

Ken G answered your questions pretty well. But this one is worth addressing again.

Dark matter and dark energy at this point are not really explanations. We observe that the expansion of the universe is accelerating. We observe that galactic rotation rates are inconsistent with the gravity that should come with amount of mass that is observed. We observe some gravitational lensing that is not consistent with the amount of mass that is observed. This is puzzling.

So "dark matter" is offered as a guess -- the guess that there is an awful lot of matter out there that we don't seem to be able to detect. And "dark energy" is offered as a guess that something is creating a repulsive effect (this is accounted for in general relativity with the addition of a cosmological constant). But we don't have an explanation, because we cannot, yet, say what dark matter is. And we cannot say what dark energy is or what causes it either. To paraphrase Prof. Muller (whose videos from the class "Physics for Future Presidents" are highly recommended --- Google it), "in the highest tradition of physics when we can't explain it, we name it."

Ken G
2009-Apr-25, 04:05 AM
There is a lot of truth to that, but it's not really quite fair. There are actual theories of dark matter, involving a range of mass of the particles that would be needed, and how such particles would actually behave, that does work pretty well toward explaining a lot of what we see. So "dark matter" (or more correctly, cold dark matter, CDM) is really an actual model. But it is not yet so well constrained, and yes, it's primary weakness is that the particles it is giving names to have never been detected in any way independent from the CDM theory itself. That's not a satisfactory state of affairs, I'd place it somewhere between a "guess" and a "law". Which end it's closer to is hard to say, and depends on who you ask-- some researchers who work on CDM are virtually certain it must be there, and will hardly bat an eyelash if and when it is independently detected. Others are more skeptical, and want to keep all options open at this point. I just don't know the body of evidence to judge who is being the more scientifically honest, but observations like the Bullet Cluster are often mentioned.

DrRocket
2009-Apr-25, 04:29 AM
There is a lot of truth to that, but it's not really quite fair. There are actual theories of dark matter, involving a range of mass of the particles that would be needed, and how such particles would actually behave, that does work pretty well toward explaining a lot of what we see. So "dark matter" (or more correctly, cold dark matter, CDM) is really an actual model. But it is not yet so well constrained, and yes, it's primary weakness is that the particles it is giving names to have never been detected in any way independent from the CDM theory itself. That's not a satisfactory state of affairs, I'd place it somewhere between a "guess" and a "law". Which end it's closer to is hard to say, and depends on who you ask-- some researchers who work on CDM are virtually certain it must be there, and will hardly bat an eyelash if and when it is independently detected. Others are more skeptical, and want to keep all options open at this point. I just don't know the body of evidence to judge who is being the more scientifically honest, but observations like the Bullet Cluster are often mentioned.

I agree that CDM offers a possibility for some of the dark matter, maybe even most of it. But I bet the researchers would bat an eye rather vigorously if it turns out to be the whole enchilada. There might even be a meeting with some of the chemistry boys who have access to ethyl alchohol. If they are right and the neutralino, a leading candidate, is a major component then I would think that the discovery of a real, no-kidding, identifiable, supersymmetric partner to a known particle ought to rate at leas an eye bat. I'd personally bet on a ticker-tape parade and a Nobel Prize or three.

They may be right. But it seems to me a bit early to call the game.

There is something of a history of over-optimism with regard to theoretical models. In his book A Brief History of Time Hawking expressed a lot of optimism that we would have a theory of everything by about ten years ago. Then string theory was going to save us all. That was followed by M theory, but the very existence of M theory is still a conjecture, and the biggest open problem is "what is M theory?" So, the cynic in me says lets wait until we have a real model, confirmed by real experiments, that show the existence of real matter before we declare the dark matter issue solved.

ryanm
2009-Apr-25, 07:53 AM
I just read up a little bit on cold dark matter, but I guess I still have some questions on this.

#1. If we are trying to detect this via background radiation and can't because it doesn't radiate any--can we try and detect what it absorbs? There should be some thermodynamics in action either way. If dark matter does not participate in the exchange of energy within a thermodynamic system--how do we account for its ability to not produce or retain heat?

#2. Are we determining the velocities we are observing to be unobtainable given mass estimations? For example, galaxy X seems to be spinning faster than it should be able to without flying apart. By the same example, can we see galactic contraction where there are galaxies collapsing on themselves with also seemingly unaccounted for mass? I would think we would see both examples of how the mass in dark matter would come into play.

In my over-simplified view of dark matter, we are saying matter exists that does not participate in at least one set of physical laws (thermodynamics), does not interact with light, but has detectable mass and mass interactions with traditional matter.

I guess, if I have to go along with it--shouldn't we see "hovering".\? If I am observing an object that should be gravitationally drawn towards another object, but seems to be holding position or progressing more slowly than expected--there has to be another force acting on the object. For example... If an object the size of our sun was close enough to another solar object, we'll just say 100x its mass--we should see an attraction between our sun and that object. Now, if we also observe that for some reason, this object does not seem to be moving towards the other super massive object in line with our estimates--can't we then guess the mass generating the opposing force at work?

To add another example, which I know is far too neat and clean---lets say this solar object is 1 light year from the 100x more massive object----and 1 light year away from an object 50x but made up of dark matter (and essentially invisible to our instrumentation), can't we almost pinpoint that gravitational source and try to make more careful observations of that area?

In this case, the path or arc of that the sun is traveling in should show a secondary favoritism towards that alternate mass area. Once we measure enough objects affected by such an area, shouldn't that give us at least a gravitatioanl view of a dark matter "blob"?

I am referencing solar sized objects because if there is enough dark matter to keep an arm of a galaxy from spinning off into space--then there should be huge blobs of this stuff out there. Otherwise, aren't we saying that we are surrounded by dark matter and its an invisible micro-particle that we interact with every day?

Ken G
2009-Apr-25, 03:23 PM
I'd personally bet on a ticker-tape parade and a Nobel Prize or three. No question the discovery of the dark matter particle will result in a Nobel prize-- for the people who find it. Those who did not find it will be glad for them, and they will be excited, but most won't actually be surprised. The surprise will be that it was possible to detect, and that will be the Nobel prize too, because it's going to take a pretty clever experiment.

So, the cynic in me says lets wait until we have a real model, confirmed by real experiments, that show the existence of real matter before we declare the dark matter issue solved.I don't know of anyone who is declaring that issue is solved. There is very little optimism that the particle will be discovered-- it is more the expectation that it is out there that is widespread. That was true even before the Bullet Cluster-- which is widely viewed as "the smoking gun". But we could always be fooled, until the actual particle is identified-- if that ever becomes possible.

DrRocket
2009-Apr-25, 06:21 PM
I just read up a little bit on cold dark matter, but I guess I still have some questions on this.

#1. If we are trying to detect this via background radiation and can't because it doesn't radiate any--can we try and detect what it absorbs? There should be some thermodynamics in action either way. If dark matter does not participate in the exchange of energy within a thermodynamic system--how do we account for its ability to not produce or retain heat?

The basic idea is that there may be some form of matter (elementary particles) that does not feel the electromagnetic force that accounts for dark matter. That is a little different from not retaining heat, which is kinetic energy at a molecular or particle level.

With regard to thermodynamics you would need to think about this in terms of statistical mechanics, but statistical mechanics that involves interactions not governed by the electromagnetic force. I'm sure that someone has thought about this, but I don't who and don't have any references.

#2. Are we determining the velocities we are observing to be unobtainable given mass estimations? For example, galaxy X seems to be spinning faster than it should be able to without flying apart. By the same example, can we see galactic contraction where there are galaxies collapsing on themselves with also seemingly unaccounted for mass? I would think we would see both examples of how the mass in dark matter would come into play.


In my over-simplified view of dark matter, we are saying matter exists that does not participate in at least one set of physical laws (thermodynamics), does not interact with light, but has detectable mass and mass interactions with traditional matter.

This is a little dated, but here is a serious tutorial by a real expert http://web.mit.edu/~redingtn/www/netadv/specr/012/012.html

And this Wiki article contains a pretty good overview including a discussion of the experimental evidence. You are pretty much on track in your thoughts, except that the distribution of dark matter does not seem to be consistent with any gravitational collapse.

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


. Otherwise, aren't we saying that we are surrounded by dark matter and its an invisible micro-particle that we interact with every day?

I think that the supposition is that we are indeed surrounded by dark matter, but we don't interact with them except through gravity. That first link discusses some ideas regarding the distribution of dark matter. But it seems to be concentrated in the vicinity of galaxies, and within them. This paper is a recent Ph.D. thesis that addresses the distributin of dark matter. http://arxiv.org/PS_cache/arxiv/pdf/0903/0903.4588v1.pdf

Cougar
2009-Apr-25, 07:03 PM
...can we try and detect what it absorbs? There should be some thermodynamics in action either way. If dark matter does not participate in the exchange of energy within a thermodynamic system--how do we account for its ability to not produce or retain heat?


Well, we account for it by saying that dark matter "particles" apparently do not participate in the electromagnetic or strong nuclear interactions, otherwise we would be detecting them. Neutrinos are much too light to account for the apparent discrepancy, but they are a good example of something that does not participate in the electromagnetic or strong nuclear interactions, and interacts only rarely via the weak nuclear force.


#2. ...galaxy X seems to be spinning faster than it should be able to without flying apart. By the same example, can we see galactic contraction where there are galaxies collapsing on themselves with also seemingly unaccounted for mass?

No, we don't see collapsing galaxies. We see that the orbital velocities of visible objects within most spiral galaxies do not generally slow down with increasing radius. This is in contradiction to the observed mass of all the electromagnetically visible matter within the galaxy (stars, gas, dust, etc...).


In my over-simplified view of dark matter, we are saying matter exists that does not participate in at least one set of physical laws (thermodynamics), does not interact with light, but has detectable mass and mass interactions with traditional matter.

Well, not with such absolute certainty, but that's one of the front-running hypotheses.


...an object 50x but made up of dark matter...

Oh - dark matter wouldn't clump like that. It only very rarely interacts with itself (other than gravitationally). So when its gravity pulls it together, it always squirts out the other side, so to speak. It's very diffuse.

.

Ken G
2009-Apr-25, 07:24 PM
#1. If we are trying to detect this via background radiation and can't because it doesn't radiate any--can we try and detect what it absorbs?No, because what does not emit also does not absorb.


If dark matter does not participate in the exchange of energy within a thermodynamic system--how do we account for its ability to not produce or retain heat?It does exchange and store energy, just not using light. There is no problem with thermodynamics, just turn off the opacity. This is already true for other kinds of "dark matter" like neutrons, for example, but they just always come with plenty of electrons around, and for neutrinos, but there just aren't enough of them. By and large, the only "bright matter" is electrons, so that's why the basic concept of "dark" matter is nothing new to thermodynamics.


#2. Are we determining the velocities we are observing to be unobtainable given mass estimations? For example, galaxy X seems to be spinning faster than it should be able to without flying apart. By the same example, can we see galactic contraction where there are galaxies collapsing on themselves with also seemingly unaccounted for mass? It's hard to see galaxies collapsing on themselves, because the timescale for them to do that would be quite quick, so if it were going to happen, it would have by now (see "supermassive black holes").

ryanm
2009-Apr-25, 09:08 PM
Thank you for the responses :) I'm glad I found this forum because I don't really have anyone to pose these kinds of questions/thoughts too here in Iraq.

m74z00219
2009-Apr-25, 10:09 PM
I just read up a little bit on cold dark matter, but I guess I still have some questions on this.

#1. If we are trying to detect this via background radiation and can't because it doesn't radiate any--can we try and detect what it absorbs? There should be some thermodynamics in action either way. If dark matter does not participate in the exchange of energy within a thermodynamic system--how do we account for its ability to not produce or retain heat?



If dm are simple particles and they don't interact with EM energies and they form no dark matter compounds, then the only thing that defines a dm particle's temperature would be its kinetic energy. So, a "cloud" of dark matter would have a temperature of ...

T = (2/(3k))*average_KE

However...since dm doesn't seem to have different electronic states, there is no kind of em emission or absorption. So, it'll have a heat capacity of something like (3/2)Nk...but all of this useless to me because there are no electronic transitions which would indicate temperature of normal matter. This also means it could only lose temperature (and thus heat) by gravitational interaction (to change its mean KE).

Perhaps this was a waste of a post (I'm rambling...) But, normal matter can exchange thermodynamic energy with dark matter by way of gravitational interaction. A cloud of dm could potentially change the mean KE of a cloud of normal matter and thus change its temperature.

Ken G
2009-Apr-26, 12:27 AM
Thank you for the responses :) I'm glad I found this forum because I don't really have anyone to pose these kinds of questions/thoughts too here in Iraq.Our pleasure, especially since it sounds like I am in the country that voted in such a way as to ask you to make the sacrifice it sounds like you are currently making.

Ken G
2009-Apr-26, 12:30 AM
So, a "cloud" of dark matter would have a temperature of ...

T = (2/(3k))*average_KECorrect.

Perhaps this was a waste of a post (I'm rambling...) But, normal matter can exchange thermodynamic energy with dark matter by way of gravitational interaction. A cloud of dm could potentially change the mean KE of a cloud of normal matter and thus change its temperature.Also correct, and that's all included in the current DM models. It's part of why DM is believed to be a good path to follow, because the kinds of exchanges you are talking about can be made to work out well and explain what we see (though there's always a few flies in the ointment, I'm sure).

m74z00219
2009-Apr-26, 01:42 AM
it's all very exciting!

Ken G
2009-Apr-26, 03:56 AM
Indeed it is, I hope it gets resolved in my lifetime.

George
2009-Apr-27, 08:10 PM
Accelerating onward with DE....

Is it correct to state that the DE at 120 orders above that currently vacuum energy level observed is very critical to BBT? I understand that the range of energy needed to be within about a factor of 10. Thus values less than, roughly, 119 orders, or values greater than, roughly, 121 orders, would be very problematic for us to have the universe that we do. If so, that seems incredibly tight as a restraint, though some see a factor of 10 as much too broad and lends itself more favorable to the multiverse idea, I think I read.

My main question is... why wasn't something so beyond gigantic in magnitude not be part of the early years of the bang idea, or at least long before accelerated space was discovered? Of coure, maybe it was known, and I must have missed this along my convoluted and contorted way. So, when did the Bang Gang, if there was one, pick-up on DE?

Ken G
2009-Apr-28, 03:04 AM
Is it correct to state that the DE at 120 orders above that currently vacuum energy level observed is very critical to BBT? I understand that the range of energy needed to be within about a factor of 10. Thus values less than, roughly, 119 orders, or values greater than, roughly, 121 orders, would be very problematic for us to have the universe that we do.It depends on what you mean by the universe we have. If you only look at it now, dark energy has not really done anything important yet. If you come back in 100 billion years, it's a totally different universe. So with some kind of anthropic kind of thinking, you might try to argue that dark energy puts us in a more likely universe, perhaps, but if you just look at the universe as we actually know it, dark energy has not played any substantial role. You can tell that from the fact that the Big Bang models seemed to give consistent results before dark energy was even discovered (if it has been discovered yet).
My main question is... why wasn't something so beyond gigantic in magnitude not be part of the early years of the bang idea, or at least long before accelerated space was discovered?I think you might have something mixed up there, dark energy is not gigantic-- it is 120 orders of magnitude less than particle physicists would have guessed, once they were told that it's not zero. Basically, you have two possible scales, zero, and what you can make from the fundamental constants, and dark energy is 120 orders of magnitude less than the latter. So it has its own scale, independent from the rest of physics, and no one knows why-- there would have to be new physics there.

George
2009-Apr-28, 04:37 AM
It depends on what you mean by the universe we have. If you only look at it now, dark energy has not really done anything important yet. If you come back in 100 billion years, it's a totally different universe. So with some kind of anthropic kind of thinking, you might try to argue that dark energy puts us in a more likely universe, perhaps, but if you just look at the universe as we actually know it, dark energy has not played any substantial role. My limited knowledge of DE, which is sadly obvious after only one post, assumed DE behaves as an emergent property that is only recently becoming the dominant player by accelerating spacetime, and that it was not considered much prior to this. In other words, with no acceleration, no DE was necessary. I was wrong, but I wouldn't be surprised if many have such a limited view. [This also means that DE could have been even lower in value and not have a negative effect on our universe, contrary to my prior suggestion.]

I'm still puzzled on how much a factor DE seems to have played in controling, along with many other factors, how our universe evolved. Apparently, Steven Weinberg, an anthropicist (sp?), has claimed that a modest increase, perhaps no more than 10x, in magnitude for DE would have limited galactic formation within the universe.


I think you might have something mixed up there, dark energy is not gigantic-- it is 120 orders of magnitude less than particle physicists would have guessed, once they were told that it's not zero. :eek: Yikes, I hate it when I'm off by 10240! [ I feel like I should start reading those Darwin Award stories to have any hope of self-preservation. :( ] As above, I took the assumption that if you want to accelerate the universe you needed something really, really big, and you hand me something really, really small. Figures! :wall:

"Less" does explain a great deal more, nevertheless. Thanks. :)

Ken G
2009-Apr-28, 06:22 AM
My limited knowledge of DE, which is sadly obvious after only one post, assumed DE behaves as an emergent property that is only recently becoming the dominant player by accelerating spacetime, and that it was not considered much prior to this. In other words, with no acceleration, no DE was necessary.That's all true, I don't see the connection with the questions in the last post.


[This also means that DE could have been even lower in value and not have a negative effect on our universe, contrary to my prior suggestion.]
Right, if DE was less, or zero, the universe of today would not be much different, although it might have been some analogous property that caused inflation (if inflation happened).


I'm still puzzled on how much a factor DE seems to have played in controling, along with many other factors, how our universe evolved. Apparently, Steven Weinberg, an anthropicist (sp?), has claimed that a modest increase, perhaps no more than 10x, in magnitude for DE would have limited galactic formation within the universe.Yes, cranking up DE would have had an impact, by causing the expansion to start accelerating too early. It's cranking it down that wouldn't do much as of yet.


:eek: Yikes, I hate it when I'm off by 10240!That could be some kind of record... :shifty:


As above, I took the assumption that if you want to accelerate the universe you needed something really, really big, and you hand me something really, really small. Ah, but what you need is something really really small that is acting over a really really big volume-- and that's just what we seem to have.

George
2009-Apr-28, 12:58 PM
That's all true, I don't see the connection with the questions in the last post. I was connecting the wrong dots. It seemed to me that DE was somewhat critical in the formation of the small anisotropy necessary for the galaxies to form, thus it should have been recognized from the get go, more or less. Now I see that DE was not that influential and easily unrecognized if we only are looking at the primal period of BBT, and ignoring zero point energy spacetime stuffings.


Right, if DE was less, or zero, the universe of today would not be much different, although it might have been some analogous property that caused inflation (if inflation happened). That's interesting. Isn't the proposed Higgs field the main character for inflation -- though, perhaps, an anti-Higgs field would be more apt a term during this very early phase? Of course, I suppose the two, DE and the Higgs Field, could be related somehow.


That could be some kind of record... :shifty: Another trophy for Georgecentricity -- though, perhaps, anti-Georgecentricity would be more apt a term during this continuous mental phase transition. ;)


Ah, but what you need is something really really small that is acting over a really really big volume-- and that's just what we seem to have. What I missed, somehow, was that the zero point energy (?) calculations demonstrated that there should be insane amounts of energy per cubic cm, and that DE puts it in its place, sorta, I think, maybe. :)

Ken G
2009-Apr-28, 02:58 PM
Of course, I suppose the two, DE and the Higgs Field, could be related somehow.Yeah, that's what I was driving at, but I have nothing specific in mind.

What I missed, somehow, was that the zero point energy (?) calculations demonstrated that there should be insane amounts of energy per cubic cm, and that DE puts it in its place, sorta, I think, maybe.
Yeah, that's the 120 orders of magnitude-- if there's energy in the vacuum, the only way we can think to estimate it comes out that high. One might imagine this energy doesn't do anything because it can't be extracted in any way, but it's very hard to imagine how one part in 10120 only could be extracted!

zhamid
2009-Apr-28, 03:10 PM
I think the science community did some disservice to non-scientists by naming it 'dark energy' and 'dark matter'. I sounds so mysterious and science-fictionist. "Unknown" or "Still to be figured out" would be better terms :-)

George
2009-Apr-28, 04:17 PM
Yeah, that's the 120 orders of magnitude-- if there's energy in the vacuum, the only way we can think to estimate it comes out that high. One might imagine this energy doesn't do anything because it can't be extracted in any way, but it's very hard to imagine how one part in 10120 only could be extracted! That's an interesting possiblity, but a little awesome to think about as this potential energy is unfathomable in magnitude.

Ken G
2009-Apr-28, 08:33 PM
I think the science community did some disservice to non-scientists by naming it 'dark energy' and 'dark matter'. I sounds so mysterious and science-fictionist. "Unknown" or "Still to be figured out" would be better termsAnd that's before we know what it is--- science tends to respect its traditions enough to keep the same name even after things have been figured out. So we still have the "Big Bang", even though we know it wasn't an explosion, and we still have "Black Holes", even though in quasars and supernovae they are the engines for the brightest objects in the universe. Indeed, a better name for "dark matter" is certainly "invisible matter", because it is invisible, and something that's invisible would rarely be called "dark". (As I recall, there is a big difference between "Darkman" and "The Invisible Man"). But things are named in fairly arbitrary ways in science-- and once a name catches on, there's a lot of inertia against changing it, so we just live with the misconceptions.

George
2009-Apr-28, 08:50 PM
I think "transparency" is yet another, and now popular, term (but that's another matter). ;)

Ken G
2009-Apr-29, 02:07 AM
Yes, I think "transparent matter" triggers the buzzword overload warning sensor.

George
2009-Apr-29, 04:02 AM
Yes, I think "transparent matter" triggers the buzzword overload warning sensor. :) Agreed, it ain't remotely catchy like "Big Bang".

We are now prepared for the next unusual substance (http://www.bautforum.com/astronomy/82605-astronomy-humor-2.html#post1474606) found:

Besides condensed matter and dark matter astromoners have recently discovered doesn't matter....which apparently has no effect whatsoever on the universe. :)