Our understanding

[velo]

Hi everyone.

 

My interest is mainly cosmology and i would love your views on its

progress/lack of.

From what i can discover string theory and quantum loop gravity do

not as yet work.

Dark matter and Dark energy are yet to be discovered, (reading between

the lines) Dark energy seems to be an unwelcome addition to cosmology.

The Higgs boson, the graviton ,predicted by some theories remain

undiscovered, (but are ever more constrained). the same with gravitational radiation.

In short it seems every way we try to explain our universe comes up

against obstacles that are as yet uncrossable.

[Bettina]

Hi everyone.

 

My interest is mainly cosmology and i would love your views on its

progress/lack of.

From what i can discover string theory and quantum loop gravity do

not as yet work.

Dark matter and Dark energy are yet to be discovered, (reading between

the lines) Dark energy seems to be an unwelcome addition to cosmology.

The Higgs boson, the graviton ,predicted by some theories remain

undiscovered, (but are ever more constrained). the same with gravitational radiation.

In short it seems every way we try to explain our universe comes up

against obstacles that are as yet uncrossable.

 

Because we are still in our infancy yet we have come a long way since the telescope.

 

Bettina

[Martin]

Hi everyone.

My interest is mainly cosmology and i would love your views on its

progress/lack of.

 

I have a 20 year perspective roughly 1987-2007

From my perspective cosmology has made amazing progress, especially since COBE (in the 1990s) and the HST and WMAP (since 2002).

 

There is a world of difference since say 1998. Like somebody turned the lights on.

 

Progress in Astrophysics and Cosmology is much faster than, say, High Energy Particle Physics (which has been fairly static since around 1980 or whenever the standard model was developed)

the annual number of papers in the various fields, and the numbers of highly cited papers, show the contrast.

 

Cosmology has become an empirical quantitative science since 1998.

Instead of speculating using rough estimates, they spend their time meticulously fitting their model to masses of data. the parameters that go into the mainstream consensus model (LCDM) are being measured with some reliability and precision. One has errorbars.

 

If you like quantitative empirical science this is really thrilling.

 

In a certain sense string theory is irrelevant, even basic things like Higgs are irrelevant. Cosmologists don't really need to know what particles make up Dark Matter----although it would be nice to know. They just need to observe how much there is and how it behaves.

 

the frustrations you mention are mainly PARTICLE physics problems.

 

they are not roadblocks for Cosmology. The field is hot. they are on a roll.

 

Here is a sample recent paper by Ned Wright

http://arxiv.org/abs/astro-ph/0701584

Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant

 

the title already says a lot. he is narrowing down the possible numbers for Dark Energy using SIX kinds of data (Supernovae data, GRB data, CMB oscillations data, etc etc.)

 

The reason cosmology is hot, the basic reason, is INSTRUMENTS especially orbital but also new groundbase instruments.

 

If you have specific questions, please ask. Several people here may provide specific responses. So far your questions is somewhat impressionistic so hard to give definite answers.

[fredrik]

In short it seems every way we try to explain our universe comes up against obstacles that are as yet uncrossable.

 

This is a general physics thing though but I am intrigued to see how we will eventually will cross these "uncrossable obstacles".

 

Is it that we just haven't found the answer "yet", or are our questions flawed and therefor doesn't have a sensible answer? Ever since I started taking interest in physics and throughout education I have had the feeling that sometimes one can spend 5 pulling out a question, and then 10 years trying to find the answer. At what point do you ask yourself if something is wrong with the question? The next step is to ask, if finding the answer and finding the question isn't almost the same thing? If that is so, perhaps an easy question with a hard answer can be transformed into a harder question but with an easier answer, if we spend more than the traditional 5 minutes thinking about the question.

 

This had little specifically to do with cosmology though.

 

/Fredrik

[velo]

Martin, i do agree that cosmology is at an exiting age, with some tests

narrowing the options to a (standard model) LCDM, my problem is, if the

foundation for this model, if the predicted particles ,are not found, then

what is the construct to this model? one could just say, this is what we

see so it must be so.

Maybe one can accept that our galaxies spin to fast without dark matter?

Or the expansion of the universe is accelerated without dark energy?

That GR works without gravitational radiation ?

Martin there is more, and i am an awkward so and so who questions almost

everything, and to my mind cosmology has a heck of a lot of things to

answer

[velo]

Because we are still in our infancy yet we have come a long way since the telescope.

 

Bettina

 

 

Bettina, i would agree if only we had a standard ruler.

[Martin]

..

Maybe one can accept that our galaxies spin to fast without dark matter?

Or the expansion of the universe is accelerated without dark energy?

...

 

Yes one could accept that, given good evidence

There are proposed modifications of the law of gravity that would make dark energy unnecessary, and also ones that would obviate dark matter.

 

I expect you know the difference between an "effective theory" and a "fundamental theory"

An effective theory is just one that gives you a good fit but may still be somewhat AD HOC.

It successfully describes the phenomena but one still is unsatisfied because it does not provide the desired deep understanding.

 

Having an effective theory is a helpful step along the way. It is better to have one than NOT to have one!

 

If you wish, you can think of LCDM as an excellent effective theory that fits the data and describes the phenomena, one just must plug in these numbers 0.73 for the DE and 0.23 for the DM. and the curious equation of state number w = -1.

 

OK that still leaves lots to wonder about! But that is how things progress.

 

Maybe a more fundamental understanding of the quantum physics of spacetime geometry will emerge from quantum gravity research.

 

This year is scheduled to appear a book by Daniele Oriti published by Cambridge University Press called Approaches to Quantum Gravity: Towards a New Understanding of Space, Time, and Matter

 

maybe this book will have seeds of an idea for an understanding of spacetime geometry interacting with matter---a better understanding of what underlies the Einstein equation of GR. And perhaps DM and DE or at least one of them will be rendered unnecessary.

 

but the effective theory LCDM will still be the effective theory and it is already a splendid achievement.

 

this is just my private opinion, but you asked for our personal views.

[velo]

As i am only a watcher/reader of cosmology and something of a realist,

i find it difficult to get excited about a theory, ad hoc or whatever, that

has a 95% unexplained component, maybe in the years to come DE, DM

will be found, but it seems to me constraints are ever tighter ,with to date

no detection, by the way i would be one of first jumping with joy if there

was.

As for quantum gravity, i have followed string and quantum loop for some

time, maybe it is time for another book to revive interest, the way

string has survived 30yrs with no testable predictions has all ways

struck me as unique.

[swansont]

As i am only a watcher/reader of cosmology and something of a realist,

i find it difficult to get excited about a theory, ad hoc or whatever, that

has a 95% unexplained component, maybe in the years to come DE, DM

will be found, but it seems to me constraints are ever tighter ,with to date

no detection, by the way i would be one of first jumping with joy if there

was.

 

One might note that the neutrino followed a somewhat similar course. Energy and momentum were violated in beta decay without it, but by applying knowledge of what was missing, the properties of the neutrino were ascertained, and it was eventually confirmed.

[foodchain]

Yes one could accept that, given good evidence

There are proposed modifications of the law of gravity that would make dark energy unnecessary, and also ones that would obviate dark matter.

 

I expect you know the difference between an "effective theory" and a "fundamental theory"

An effective theory is just one that gives you a good fit but may still be somewhat AD HOC.

It successfully describes the phenomena but one still is unsatisfied because it does not provide the desired deep understanding.

 

Having an effective theory is a helpful step along the way. It is better to have one than NOT to have one!

 

If you wish, you can think of LCDM as an excellent effective theory that fits the data and describes the phenomena, one just must plug in these numbers 0.73 for the DE and 0.23 for the DM. and the curious equation of state number w = -1.

 

OK that still leaves lots to wonder about! But that is how things progress.

 

Maybe a more fundamental understanding of the quantum physics of spacetime geometry will emerge from quantum gravity research.

 

This year is scheduled to appear a book by Daniele Oriti published by Cambridge University Press called Approaches to Quantum Gravity: Towards a New Understanding of Space, Time, and Matter

 

maybe this book will have seeds of an idea for an understanding of spacetime geometry interacting with matter---a better understanding of what underlies the Einstein equation of GR. And perhaps DM and DE or at least one of them will be rendered unnecessary.

 

but the effective theory LCDM will still be the effective theory and it is already a splendid achievement.

 

this is just my private opinion, but you asked for our personal views.

 

Could dark matter just qualify as a title for matter that’s not part of a galaxy or larger body that emits something detectable. Such as just basically "inert" rock floating in space for instance. I just don’t see a nebula, or the theory of such as how it relates to planetary or star formation for instance as being able to draw in every bit of matter, though the matter on the fringes could be effected by such still, but via the nebula itself be somewhat ejected away from whatever does become of such, the nebula that is. Or for that matter galaxies. I just try to imagine that in the “vacuum” of space I doubt for any physical forces to exist, or matter and energy being absent from the equation how could anything do anything, but on that idea does all matter that existed then simply exist just in galaxies for instance, or it is possible that out in space there just might exist intensely large asteroid fields for example. I mean from big bang--à to present, could all the matter really have been absorbed by galaxies, or would the big bang produce a big nebula, or really what’s going on I am so confused.

[velo]

Foodchain, this is what Wikipedia has under Dark Matter

 

 

The Concordance Model requires that, to explain structure in the universe, it is necessary to invoke cold (non-relativistic) dark matter. Large masses, like galaxy-sized black holes can be ruled out on the basis of gravitational lensing data. Possibilities involving normal baryonic matter include brown dwarfs or perhaps small, dense chunks of heavy elements; such objects are known as massive compact halo objects, or "MACHOs". However, studies of big bang nucleosynthesis have convinced most scientists that baryonic matter such as MACHOs cannot be more than a small fraction of the total dark matter.

 

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To date i think it is (accepted) that 95% of all matter is Dark Matter.