ajb

So i understand what you mean by this, there was a 1 in 100,00 chance that temperatures would be variant in the pattern they were described?

No, this is the scale of the differences in temperature as compared with the average. This means that the CMBR is quite uniform until you get to 1 part in 100,000.

There are also some hot and cold spots in the CMBR that are unexpected and may just be down to not subtracting the local environment properly.

On the subject to this ring structure, you can read the paper here http://arxiv.org/abs/1507.00675

The point is that it seem to be too be larger than the scales that we would expect the Universe to appear homogeneous and isotropic. This violates the cosmological principle, which is of course an approximation - though thought to be a good one.

I just dont understand how someone can look at pictures of the CMB and call those anomalies "small". [/size][/background]

The temperature fluctuations are something like 1:100,000. We think this is quite small - but what we expect from theory.

Riiiiight, but you aren't dense enough not to understand the implications of the CMB being anisotropic.

Sure - the anisotropies are small but very important, for instance they are linked to structure seeding in the early Universe. I think that Strange also knows this.

Nah, sorry. You cant have both ajb its either the cosmological principle or nothing, there is no in-between here bud...no matter how much you and strange want to minimize the findings.

I am talking about the CMBR and the scale of the fluctuations.

The ring of gamma ray bursts is something else. If these bursts really are all connected then they form a larger structure that the current models really allow - and the details of the CMBR support the current models. So, either it is chance that they formed in this way they have, or some of the data on their positions is poor, or we have to think more about the models. Interesting stuff either way.

"A question of scales" you say eh?

Yes - the CMBR has very small fluctuations in temperature when compared to the average. This is well established science.

Why did they send up so many satellites then?

To carefully measure these small fluctations... and remember there has also been balloon made measurements.

If it was as minor as you and strange say, why didnt they write it off in 1982 or whenever the first time they mapped the CMB?

Because the details of these small fluctuations are important in understanding models of cosmology. They are like the fingerprint of the Universe and allow us to rule out certain cosmological models. So right now the best model is the Lambda CDM model with inflation.

I think you are misunderstanding the fact that these fluctuations are small with the idea that they are not important. None of us has said that these fluctuations are not important - just that they are small and that the CMBR is near homogeneous.

Is it possible for you to translate your last ( clearly very significant ) comment about the nature of space-time and its ( medium style ) workings with em and gravity waves .

Space-time has 'two parts'

i) the structure of a smooth manifold of dimension 4 - meaning locally it looks like R^4.

ii) on that manifold we have a metric of signature (-1,1,1,1) (or (1,-1,-1,-1) depending on conventions)

The manifold structure we think of as the collection of all possible events - we don't dwell too much on what that means. The metric structure gives us a notion of the distence between two near by points, which we can also use to denfine the length of paths joint two points. This really encodes the causal structure.

Gravity we can think of in terms of this metric - the metric is like the gravitational potential found in Newtonian gravity. When there is no gravity the space-time is Minowski space-time, but when we have gravity the metric is different to the Minkowski metric.

Now, we like to measure how this is different. To do this we construct a connection - which gives us a way of moving vectors from one point to another near by point - and then we look at the curvature of this connection. We can think of the gravitational degree of freedom in terms of this connection rather than the metric.

We can do something similar in the case of EM, but we start with a connection (on a specific fibre bundle over the space-time) which we understand as the potential A. The field strength is the curvature of this connection (all mod possible plus or minus the complex unit).

Nothing about the CMB is homogeneous at all.

It is very nearly homogeneous and the scale of the fluctuations is very small compared to the average temperature. It is all a question of scales.

As for the possible structure you ask about - I have no idea, it is far from my area of knowledge.

It's possible that he should "walk away" happy in the knowledge that the answer to his questions were "no" and "yes".

You are right - so I we change my statement to 'one could look up Galois theory to understand the reasons why the answer is no'.

If I can party poop ,by that definition can the Gravitational Field also be seen as a medium for EM waves and so EM waves would have 2 mediums, the Gravitational Field as well as the EM field.?

Both the EM and gravitational field need space-time thought of as the underlying manifold of 'events'. But be careful here, gravity is really the local geometry of space-time and not 'just' space-time.

Gravitational waves are ripples in the local geometry of space-time - or really the frame bundle thereof - and electromagnetic waves are ripples in the local geometry of a U(1) principle bundle over space-time.

It is impossible in general for polynomials of order 5 and above - see the Abel–Ruffini theorem which states there are no algebraic solutions of such polynomial equations.

Note that this does not mean there are no solutions (real or complex), just that you cannot write then in an algebraic form (in terms of radicals). Also it does not mean that you cannot find algebraic solutions to some polynomials of higher order.

You should also look up Galois theory which is the theory that deals with this question properly.

Please expand further - By that I presume you mean experiments such as Gravity Probe B lend support to the substantivalist (Space-Time as a Physical Entity) view as opposed to the relationist view?

You take a peice of paper and a pen, and do some calculation that say I will measure some value of something to be X. I then do some experiment and I see that I do, near enough measure the value of that thing to be X.

We can claim no more that this.

A great cover... I won't make you suffer the original

It is like good porn - you know it when you see it, but can't quite describe it to others.

By the tests of general relativity matching 'Physical Theory' do you mean the substantivalist view of Space-Time?

I am not sure we can decide what metaphysical view of space-time is correct. All we can really do is put our models to the test - and with that general relativity works. I don't think one can say a lot more..

A ' real thing ' as opposed to a 'mathematical thing '.

You will have to think carefully about this. As all our interpretations of experiements and observations require a mathematical model, can you really separate the two?

You speak of a field , which field ? The Field , that is out there , permeating all space and the universe .

Without introduces the other forces at this stage, lets say the electromagnetic field and the gravitational field.

If so, where did this field come from , I am saying it came from dark energy ...

The problem is we don't know what dark energy is and so saying that it gave rise to the fields of the standard model - or just gravity and electromagnetism - is just a story. You need so show some mechanisms here.

As to where the fields came from, we don't really know. What we do know is that with supersymmetry all the running couplings ('interaction strengths') of the standard model come together at a high enough energy. This suggests, in the same sort of way as electromagnetism and the weak force can be unified, all the fields of the standard model an be unified. This leaves out gravity, however maybe at or near the Planck sale a full unification is possible. We just don't really know.

Now , steady up there , . This is where I have to watch , you don't take me off in a maths rapture , and you leave me for dead by the wave side ! I have to check you have not subdueced be , away from reality .

Well, what is the problem?

Do you have a real objection to the electromagnetic field as a mathematical object? You can understand this field in terms of some differential geometry - it is related to a connection on a U(1) principle bundle. Not that details matter at all, just that we do understand EM in terms of geometry.

In a similar, but different way, we can understand the gravitational field to be a mathematical object that encodes all that we need. This object we understand, again in terms of differential geometry - in the standard formulation we understand the gravitational field to be a metric tensor. But we can also understand it it terms closer to EM as a connection on a principle bundle known as the frame bundle.

Again, details are less important than the ideas. You will have to think about the objections you have to gravity and if these are really any different to your objections to electromagnetic theory.

I personally find this contradictory...

I don't think that Einstein was greatly interested in metaphysics and so I would not be surprised if you can find differing quotes.

I know for sure that he was not impressed by some philosophical views on time.

Someone like Brian Greene for example in his book 'Fabric Of the Cosmos' makes it specifically clear that he regards space-time as a physical entity and not a mathematical abstraction which I guess would make him a substantivalist...

He is free to hold that view. The problem is that as our understanding of space-time changes, and it must do at some level when we take quantum effects into account, will the classical view of space-time still be 'physical'?

I am not sure, other than mathematically we should have a good understanding of how the classical notion comes from the quantum one - otherwise we will be at a complete loss as to why classical general relativity has worked so well so far.

...in a recent documentary he expressed his belief that Gravity Probe B which measured an effect on space-time curvature provided evidence to support this view, how plausible is this claim?

All the tests of general relativity tell us that the physical theory matches nature very very very well. I don't think one can really say much more.

Electromagnetic waves originate from accelerated charges.

Gravitational waves originate from accelerated masses.

The problem is also one of language here - by medium one usually means a mechanical medium, something like how sound moves through the air. By a wave, we of course need something to 'wiggle' and we have been saying more-or-less from the start that we usually think of wave solutions to some field theory. For example, a gravitational waves is a little 'wiggle' in the gravitational field - which we understand to be the local geometry as described by a metric tensor.

I dedicate this to someone who was special - you know who you are.

I can imagine that as theoretical physics advances some metaphysical questions will evaporate - but only to be replaced with others!

Very interesting, so did Einstein himself have a substantivalist or relationist view of Space-Time?

" ... In my opinion the answer to this question is, briefly, this: as far as the propositions of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality. ... "

Albert Einstein, "Geometry and Experience", 1921

Which shows that if physics progress enough to explain the problem of time, the metaphysical issue may vanish.

But there is no problem of time as time is inherent in mathematics, right?

IOW that the metaphysical arises only because there is no affordable explanation from the physicists.

In a sense I think you are right. Physics deals with mathematical models and matching them with nature. Physics does not really say much about what 'exists', what is 'real' and so on. Physics is about what we can calculate and measure - and if we can measure it then it is 'real'. But this definition I am sure will fall flat on its face if we think about it too hard!

Though a layperson, I have been saying this in so many words in more than one post now.

We have all been saying this all along...

It's obviously an error in translation. They probably meant David's projectile broke the speed of sound. I'm pretty sure the Hebrew word for "sling" is very similar to the Hebrew word for "rail gun".

Physics at the time of writting of the old testament had no idea how fast light travels - if you could not see the projectile in flight then did it more faster than 'sight'?

Anyway, the paper is total trash in a really stupid journal. Publishing it was not fair on the guys who wrote it - they actually think they have done something meaningful.

Now, rejection I doubt would have changed their minds on this.

Waves just can't exist without a medium to wave about in !

In a sence you are right - but this need not be a mechanical medium. We don't need some rubber sheet or chains of particles or anything like that.

Electromagnetic waves are ripples in the electromagnetic field (the potential A) and this field itself is 'the medium'.

Gravitational waves are ripples in the gravitational field (so the metric in the standard understanding) and this field itself is `the medium'.