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The cosmologies described here are based on the inference that the universe is expanding in a manner proportional to the observed roughly constant redshift-to-distance ratio (Hubble constant). The idea is that as space is stretched, the wavelength of light is stretched along with it, as it transverses that space.

The problem with all these mainstream cosmologies is that observations have been made that require rather different (non-cosmological) mechanisms for redshift to exist. Halton Arp has made and detailed these observations, and the surrounding controversy http://www.amazon.com/Seeing-Red-Redshifts-Cosmolo gy-Academic/dp/0968368905. Paul Mermet is another astrophysicist that has studied the matter http://www.newtonphysics.on.ca/HUBBLE/Hubble.html.

Essentially, current mainstream cosmology is likely to be complete bunk, because it is predicated on one particular ill-founded interpretation of redshift.

Gee, we would have missed out on Anomalous acceleration if we had pulled the plug the first time they wanted to. (Have they adequately explained that yet?)

One proposed explanation is here. I have no idea what the consensus opinion is.

BTW, it was Pioneer, not Voyager, that revealed the phenomenon.

I can't comment on all of his site, but this page should provide a good example of his crank-ness.

His argument is, in a nutshell, "quantum mechanics is wrong, because it doesn't make sense to me". However, he doesn't seem to provide any alternative explanations...

The author of the site is (or at least was) highly reputed. It was also him who first pointed out that the so-called gravitational anomaly, found by Pioneer spacecrafts, probably has a simple (Newtonian) explanation: dust in the Kuiper Belt--and this explanation has been entirely ignored by most physicists.

Some physicists seem to prefer complicated explanations over simple ones.

The author of the site is (or at least was) highly reputed. It was also him who first pointed out that the so-called gravitational anomaly, found by Pioneer spacecrafts, probably has a simple (Newtonian) explanation: dust in the Kuiper Belt--and this explanation has been entirely ignored by most physicists.

Some physicists seem to prefer complicated explanations over simple ones.

I like the following explanation of the anomalous acceleration. No dark matter/20 dimensions/new gravity theory needed here. A small amount of dust in the kuiper-belt that transfers momentum with the probe should be enough to explain the slowdown. Look at: http://www.newtonphysics.on.ca/Anomalous/Accelerat ion.html

According to this paper, it could be drag from dust in the outer solar system.

I guess there are a few professional rocket scientists hanging out here (and plenty of amateurs...), so now is a good time to ask a question that has bugged me for a long time:

Has any consensus been reached over what has caused the unexpected change in velocity of the Pioneer 10 and 11, Ulysses and Galileo probes? Remember this?

Since this was announced I've done some regular googling to see if this has ever been adequately explained. There are plenty of pages out there with plenty of theories, but most of the sites discussing this also have theories about things like zero-point energy generators, perpetual motion machines, that sort of stuff... Hardly the sort of thing that smells of proper scientific method.

Other theories include drag from dust, Changing velocity of light and "tired light redshift" (what the HELL is THAT???)

I have found this paper, which looks very interesting, and much more authoritive, but its is unfortunately waaay over my head!

There is still a lot of discussion on this topic, can any astrophysics lurking here comment? Are we looking at a modification of gravity? Does this tie in with dark matter/energy?

Ta :)

It isn't that convincing to me. It's too smooth to account for our 'clumpy' universe. See, for example, the third paragraph of this page. Something worth thinking about, if nothing else.

Actually, many scientists believe that the earth is at the center of the universe

Actually, not.

The attenuation of gravity, according to one of the papers I ran across is about a kiloparsec, or about 3,300 light years from each single source.

It can help get around the apparent contradiction that intact spiral galaxies present.

Regardless, the attenuation is one of the predictions of one of the theories, and can be used to prove or disprove it. Currently, very little resources are being expended on such observations. Even Majorana's careful gravity shielding experiments have not yet been redone.

Other LeSagian-type theories make no such assertion at a distance, but still modify the Newtonian equation for the insides of bodies. They establish upper and lower bounds on the strength of gravity with a 'weak' solution (negligible graviton absorption) to a 'strong' solution (complete graviton absorption).

Gravity at long distances is still open to interpretation. You have some of the more recent cosmological theories posit cosmos-wide antigravity to 'speed up the expansion of the universe', and other more mundane Big Bang interpretations assuming that the universe is flying apart, there's the "Great Attractor" purportedly pulling us towards it, but is still red-shifted.

As to the anomalous acceleration of the Pioneer probes, there's another potential explanation with some good links to various other explanations.

We're unfortunately a bit hamstrung in that we can rarely ever see phenomena happen, so a lot of interpretation of what we see - and those are what frequently get overturned.

On a more personal note, I'm just a little shocked at how much the 'party line' is expected to be followed in most fields of physics. In biology, there's not nearly the same embarrassment about being wrong, and it's a vibrant field. In physics, most work outside of quantum physics and computing seems (on a relative scale) practically dead.

So, a special plea from me to revive the field.

("No, sir, it's not dead, it's resting" :)

You'll enjoy reading this then!

I sorted out my confusion on this FAQ web site.

I made it a few pages down the FAQ, and I'm afraid I have to say that it's one of the worst that I've ever seen. The author's argument seems to amount to "Well, you can describe the universe mathematically using four dimensions, but because I only see three of them this is purely bunk.".

At this point, I stopped reading.

In point of fact, if you want to see the effects of space being four-dimensional, you need only look at two reference that are moving quickly with respect to each other. The time and space directions measured by observers in each frame are different - this is the Lorentz transform (if I remember the term correctly). Space in one frame corresponds to a skewed space-and-time axis in another frame.

This has been verified experimentally by very careful measurements of atomic clocks moving at different speeds with respect to each other. A more dramatic illustration is measuring the decay times of unstable particles moving at different speeds. As they approach the speed of light, the lifetime as measured by the observer gets longer. This is called "time dilation", and is one of many effects caused by the "time" and "space" axes not being the same for observers moving with respect to each other.

You can find a very good FAQ on relativity here:
http://math.ucr.edu/home/baez /physics/relativity.html

This links to a FAQ on general physics, and many other FAQs that may be of interest.

I sorted out my confusion on this FAQ web site.