Dark Energy

[xelasnave]

I have proposed my ideas as to the nature of dark energy in an effort to have others tell me I am wrong ( I learn more by my mistakes so I like that system) but I suspect that approach must be seen by others as me saying lets have an arguement that I have decided I am going to win.
So I make this promise anyone offerring me clues or their ideas will not be met with any arguement. I will greatfully read your opinion or the links but prefer casual "chat" type of view in loose terms presenting any view on dark energy as it fasinates me:eyepop: .
But I promise I will respond with no more than a thank you for the help rather than say yes but its really this way approach:) . No matter what comes out of this I will not oppose but thank you for your welcome input:D .
Please offer a view on it if you can. I know most of you are so much better equiped to comment than I am.:help:
I know my rantings on dark energy (ok most things) is cause enough for my plea to be ignored but I really value your input. It is the only way I can move forward. Science moves forward on firm ground I except that and would not like to see it any other way but please a little speculation and I will not argue the toss:) . and I will be humble so its worth having a go just to see that miracle dont you recon:lol: :lol: :lol:
alex

[xelasnave]

Sorry to present such a difficult question I went looking for answers early today. It seems to be a very speculative area of thought dictated bt the observations suggesting that not only is the Universe is expanding but the expansion is speeding up. I dont agree but as it suits my purposes I will go along with it;) .
Here is a snip from Physicsweb this morning
"The existence of gravitationally repulsive dark energy would have dramatic consequences for fundamental physics. The most conservative suggestions are that the universe is filled with a uniform sea of quantum zero-point energy, or a condensate of new particles that have a mass that is 10-39 times smaller than that of the electron".
I knew it this could be the gravity rain particle I have imagined. Speculation only but it suits my idea of it would have to be small even in relationship to the electron.

Anyways goto go found some good leads and I cant wait to follow them.
alex

[Doug]

Alex, what ever happened to the idea that like charges repel?
If scientists are looking for a force of mutual repulsion, the only seemingly obvious culprit would be the old 'Like forces repel' It seems that it isn't limited to electrostatic charges either. Any hypothetical particle smaller than an electron would most likely be hard put to have a net electric charge.
Ok, so I'm maybe 120 years or so out dated on my science knowledge, but elementary particles can and do have a magnetic moment; they can interact with an external magnetic field. It could be that even at the elementary particle level magnetic moment interaction might account for the proposed dark energy effect. Even elementary particles it seens have an intrinsic spin moment. Gravity rain? maybe some relationship could exist at this level to the hypothetical gravitron, I don't know. I have yet to see any evidence of gravitational self repulsion, which leads me to think that gravity is an effect rather than a force of or in itself.

To sum up, if 2 elementary particles having an intrinsic magnetic moment come close enough to each other, mutual repulsion might well be observed.

Doug

[PeteMo]

Alex just another whacky idea, but what if it is gravitational attraction that is causing the galaxies to disperse from each other by some greater mass drawing them that is beyond the limits of our telescopes? Also, how do we explain galaxies like the Andromeda heading towards us when other galaxies are heading away at an even greater rate of knots.
The existence of dark matter would seem to help explain things better than gravity alone.

[Doug]

Petermo posted:
Would this mean that the universe as we perceive it, would be suspended in a humongous shell? Such that that model would be analogous to something like the yolk of an egg being stretched to ultimately be smeared over the interior of the shell?

Interesting thought:confuse3:

[xelasnave]

AS promised I thank you Peter and I thank you Doug.
Whilst reading about dark energy I had to laugh when one article sort to explain it, another then said scientists were having second thoughts and the another saying the evidence for dark energy is growing.
Thank you very much for taking the time to offer an input I think about everything that I see and hear about and am always ready to sit back and hear the views in respect of this exciting aspect of our Universe.
Thank you
alex

[mill]

For what it is worth, here is my opinion on dark energy and why the universe is expanding at a accelerating rate and not at a decreasing rate.
Scientists think that dark energy acts as a sort of vacuum energy.
So what i think is that there is more dark energy outside the universe than inside the universe and that would also explain the accelerating expansion of our universe.
Ps: this is just my observation from reading some articles about dark energy and to me it sounds very logical :P

[xelasnave]

Mill thank you also for taking the time to consider the information that has come before you and posting something that helps me think about the matter.
I really appreciate you making the post
alex

[AGarvin]

This is because within our local group and local supercluster, galaxies and clusters are gravitationally bound. Beyond that, distances are to great and cosmic expansion dominates over gravity. There is slight variation in galaxy redshifts, the source of which has been dubbed the Great Attractor, but it is not enough to overcome the Hubble flow.

On the subject of dark energy, I'll have to defer to the professional community. We seem to have plenty of observational evidence that there is a repulsive energy at play, but no real theory to explain what it actually is. I guess for me the neatest explanation is the cosmological constant, as it based on our two existing theories, General Relativity and Quantum Mechanics.

Andrew.

[xelasnave]

Thank you for your contribution Andrew and indeed the existence of dark energy from observation makes one wonder if the great man was in the middle of his greatest blunder I have felt for some time he was in the middle of his greatest insite. Over the last 12 months it appears others see it similar. Thank you again.
alex

[PeteMo]

Hi Alex it seems that we assume that the universe is as big as the limits of our observation. We may only be glimpsing a tiny fraction of the true universe. We also tend to think 'finite', that everything must have a beginning and an end, so it is natural for us to apply this to the universe.

Andrew thanks for straightening out my logic. It looks like our local group have sufficient mass to prevent the galaxies within form being 'flung away from each other'. This got me thinking could it be some kind of centripetal force that is 'repelling' galaxies away from each other? I'm assuming that all galaxies revolve around some kind of central point in the universe.

Doug, I like your analogy of an egg, it explains what I was thinking better than I could verbalise it. I was working from the assumption that since we date the age of our universe on how far back we can see, so there could be more out there beyond our present observational limits. What if we are only seeing just 1% of the universe and basing all our observations on that? That means there would be 99% out there that we can't see (yet), and assuming similar composition of matter and mass to the parts of the universe we can see, could this account for the galaxies accelerating away at an ever increasing rate to a greater mass beyond our limits? I realise I have no empirical evidence to support any of this, hence it is just an idea.

From a documentary I saw a few months ago, there seem to be indications that dark matter exists, and seems to present a more accurate model of the universe that we are observing.

[AGarvin]

No worries. The thing to understand with the expanding universe is that even though galaxies billions of light years away are receeding from us at incredible speeds (even faster than light), locally through their own space they would only be moving around the same speed as Andromeda is as it lumbers slowly towards us. This is because it's actually the space between them and us that is expanding.

Hope that makes sense.

Andrew.

[xelasnave]

Peter I happen to think the Universe is infinite in time and the other dimentions... only because I cant imagine it floating in a sea of "nothing" I certainly dont think the Universe stops where our observations sign off.
The expanding of space is the point to get ones head around. Galaxies in their space as Andrew said may have the same speed in that part of space as we do but the point is the space between us and them is expanding... er but I am not sure of that either but thats the popular thought as I read it.
People say well how can we have them travelling faster than light..well they are not in fact it is the expansion of space that accounts for seeing them travelling so fast...mmm I think thats it. Observations support this idea or theory possibly a better way to put it a theory being really almost an established fact in this context an idea being an unsupported notion. Big bang is a theory gravity rain is a notion or an idea.Bail me out someone if I have anything wrong or if you think you can add clarity please. But Andrew has realy said that.
alex
alex

[ispom]

It will take still some years, until the supernova /Acceleration sample (SNAP)
http://snap.lbl.gov/ (http://snap.lbl.gov/)
brings us clarify of the question:

is „the dark energy “(70 per cent of our universe consists of) the by Einstein postulated „cosmological constant “or is it the second possibility considered by the cosmologists: a „quintessence “?

in the first case we would have an accelerated expansion never ending, our universe becomes more and more empty and bleak, until remaining only a lepton desert.

the accelerated expansion by the quintessence sketches however a less hopeless future picture, because after this conception the accelerated expansion continues only briefly.

now I ask myself (and the others): the ominously „energy of the vacuum “, http://en.wikipedia.org/wiki/Vacuum_energy (http://en.wikipedia.org/wiki/Vacuum_energy)
postulated by the quantum theory, is that a cosmological constant or is it a quintessence???

[xelasnave]

Thanks for that input, I recall an article I must find it, and in that it says as much and includes another proposition I must look it up.
alex

[PeteMo]

Andrew, one thing puzzles me about the expanding space between galaxies. If we use their distance and recessional velocities to extrapolate back to a point of origin (say the big bang), if their speed appears to be in excess of c, how can we accurately measure their true distance from us? Can we accurately measure the component of their recessional velocity that is due to the expansion of space?

[Karls48]

I’m also very sceptical of our present ability to measure speed and the distance of the objects millions of light-years distant. After all it is well known that the certified scientific instrument (speed camera) can clock lamppost at 48km/h and park car at 16km/h.

[AGarvin]

From what I understand there is still considerable observation going on to try and fine tune and calibrate the tools we use to determine these distances. This is why astronomers have been chasing down Type 1a supernovas. Type 1a SN are believed to be white dwarf stars that accrete mass from a companion star that has gone red giant. When they reach 1.44 solar masses (called the Chandrasekar limit after the physicist who discovered it), they detonate in what is basically a carbon bomb. Because they all detonate at the same mass and are pretty much made of the same stuff, they will all have pretty close to the same absolute brightness. Using this, we can then infer their distance by applying the inverse square law using their apparent brightness. I think it was through Type 1a SN observation that the acceleration of the universes expansion was first discovered...hello dark energy, but don't hold me to that one.

When Type 1a are discovered, they can then be used to help calibrate other tools such as Hubbles redshift distance law. This law basically relates distance and velocity to redshift. It uses what is called the Hubble parameter which is currently estimated at around 72 metres per second per megaparsec. In other words, for every megaparsec away an object is, its recessional velocity increases by 72 metres per second under cosmological expansion....and yes, local motion through space, known as peculiar motion should be taken into consideration, but hey, when something is 5 billion ly away, what's a few million among friends :P .

Andrew.

[PeteMo]

Hi Karl
I like the analogy, but although there are speed devices, they are designed for specific applications. for example, a speed radar gun designed to capture the speed of tennis balls, will give false readings on stationary cars it is now outside the operational parameters the gun was designed for. A Multanova on the other hand will not detect a cycle very well because there is not enough metal to return a radar signature. All equipment is based on some operational assumptions.

I think calculating the age/size of the Universe it's a bit like when the Ancient Greeks like Aristarchus tried to calculate the distance between the Earth and the Sun, their methodology was right based on calculating angles, but they had no accurate means of taking measurements of these angles. Hence the maths was correct, but based on wrong measurements gave the wrong answer. They did eventually arrive at a value of half the 92 million miles.

I wonder if our calculations to determine the age and/or size of the universe suffer in a similar manner, but for now it's the best we have to go on.

Pete

[PeteMo]

Hi Andrew, where did you learn all this stuff? I only learned about the basic Type I and Type II SN on my Astronomy course at Uni. Mind you that was over 11 years ago. Now each Type can be broken down into further sub groups.

I used to think that once a star was over 8 solar masses we saw CNO (Carbon Nitrogen Oxygen) reactions predominantly replace the PPI and PPII type reactions. Does this apply to a star in it's White Dwarf stage as all the Hydrogen should have been converted to Helium?

Apologies for the questions, only it looks like you have more advanced knowledge than I do.
Pete

[AGarvin]

Hi Pete,

No problems with the questions. If I can answer I'll will, if not .... I'll stay out of it.

The onset of the CNO cycle is related to the level of impurities in the star (ie, heavy elements) and temperature. I think (?) it's at around 2 solar masses that the CNO cycle begins to dominate in main sequence stars. It plays no role in a white dwarf as a white dwarf is a dead star. It's the left over core of a star after it's red giant stage. There is no fusion going on in the star and they're held up from collapse by what is call electron degeneracy pressure (a quantum thing based on the Pauli exclusion principle). It's generally believed that stars below 8 solar masses will end up as white dwarfs. Basically they're not big enough to produce enough pressure and heat to allow fusion beyond carbon. The core ends up a white dwarf and the the outer layers just slowly blow away and leave behind a wonderful planetary nebula for us to observe. The Sun will end up a white dwarf at the end of its life. Stars above 8 solar mass are believed to end up going supernova leaving behind a neutron star or black hole. They are large enough to allow fusion beyond carbon. When they hit iron fusion stops as energy has to be supplied to fuse beyond iron. Splitting atoms (fission) beyond iron is what produces energy, eg, atomic bomb.

Cheers,
Andrew.

[PeteMo]

Hi Andrew
Thanks for that. According to my old notes we had CNO Fusion as the dominant process in Main Sequence stars >8 Solar Masses, and the elements heavier than Iron produced by Type II SN. I was quite surprised at how small a white dwarf was considering the amount of matter crammed into it can be up to 1.5 Solar Masses.

One thing that still puzzles me is how to determine whether a Type II SN will become a Black Hole (like the Type I 30-40 solar masses) or a Neutron Star. This is one thing I never fully understood.

I know a lot can happen in a decade, so appreciate your explanations.

Pete

[AGarvin]

Now you've got me curious. I'll do a bit if research and see if I can clarify when the CNO cycle becomes dominant in main sequence stars. Certainly the heavy elements come from Type II SN and Type Ib/Ic SN.



I don't think anyone knows or can predict this that I'm aware of. From what I understand it's also entirely possible that neither is left and that the entire star blows up, core and all.

We seem to have hijacked this thread away from its topic (sorry Alex).

Andrew.

[xelasnave]

Andrew and Pete,
there is no need to be sorry you are covering very interesting stuff that many will love to follow, I urge you both to continue. Maybe the outpouring of energy contributes to dark energy.. have you thought of how a star blasting itself apart may help form a pressure in space for example. Just a thought to keep you guys rolling. Thank you both for having a discussion on these matters as I feel it is indeed relevant to the matter at hand and if its not who cares its neat stuff.
alex

[DobDobDob]

Digging up my 8 year old notes, I find this interesting summary of the CNO cycle.

For the CNO cycle to proceed, there must be 12C nucli present. While this is the most common isotope of carbon, it makes up only a tiny fraction of a star's composition. Not much is needed, however. Furthermore, the 12C nucleus is restored at the end of the cycle, so the process does not use up any carbon.