Einstein's Theory Improved?

skaet writes to tell us that A Chinese astronomer from the University of St Andrews claims to have fine-tuned Einstein's theory of gravity. Dr Hong Sheng Zhao has created a 'simple' theory which could "solve a dark mystery that has baffled astrophysicists for three-quarters of a century." This new law seeks to discover whether Einstein's theory was correct and if dark matter actually exists.

Comments

Dark matter eh.

[squoozer]

I'm sure that there are lots of people that are far more clued up on this than I am that can find holes in what I am about to say but I always felt like dark matter was a bit of a fudge because we don't understand what is happening.

My problem with dark matter is that it's almost as difficult to believe in as God. The only real proof we have is that the universe doesn't appear to move correctly without it. If that's as good as we can do then we might as well say God (or the FSM) is holding the universe together. To my mind it is a big leap from "the universe isn't moving as we expect" to "90% of the universe is made of something we can't see". Surely if the universe was full of this stuff we would be able to detect it because it would block radiation from distant galaxies - or is dark matter conveniently transparent?

Re:Dark matter eh.

[squoozer]

I certainly don't have a problem with the idea that we don't know everything. Perhaps my problem with dark matter is that it is reported in the press almost as if it is almost fact and yet in reality we haven't got any direct evidence. All we really have to go on is the fact that if dark matter didn't exist things, such as galaxies, wouldn't look like they do. If I had gone to my supervisor with an argument like that when I was doing chemistry he would probably have laughed himself stupid right before he sacked me. As for it not interacting with radiation thinking about it even if it did it could still be very hard to see. After all the universe is very big - you could easily hide something in it.

In the spirit of good science hence forth I am going believe that the FSM holds galaxies together with his noodly appendages. The reason the speed with which the universe is expanding is increasing is easly solved by saving that the universe is created by the FSM using lazy initialization. We gain the ability to see further faster so the FSM has to push on the edge of the universe harder hence making the universe expand faster. Simple really.

Re:Dark matter eh.

[i_should_be_working]

But our theories of gravity don't actually come from what we see. Back in the day the original gravitational theories may have been discoverd from looking at things falling and celestial objects moving through space. But nowadays gravity (and other forces/theories) are tested without actually looking at stuff (unless you count looking at the measurement apparatus to see the result). The gravitational force of various objects is routinely measured to extremely high precision without anyone having to 'see' anything.

My only point was that photons are only one of many particles and carry only one of four fundamental forces. All of those other particles and forces can be used as observational tools independent of photons. And observations based on them are just as valid. People saying that our evidence for dark matter is sketchy because it relies on gravity instead of light to observe it is like saying evidence for radiation in a room is sketchy because our particular detectors rely on the weak force and a click that we hear when a decay happens.

Re: Dark matter eh.

[Black Parrot]

> All we really have to go on is the fact that if dark matter didn't exist things, such as galaxies, wouldn't look like they do.

We also have the fact that dark matter explains why things do look like they do.

> If I had gone to my supervisor with an argument like that when I was doing chemistry he would probably have laughed himself stupid right before he sacked me.

If you went to him with a (valid) argument that chemistry AWKI makes wrong predictions about some easy and repeatable observations, would he have sacked you?

If you followed up with a hypothesis that explained all the anomalies with a single simple mechanism, would he have sacked you?

> After all the universe is very big - you could easily hide something in it.

Yes, but that something would have to be in the right place to explain the gravitational anomalies, and given our observations of that place, it would have to be "hidden" in a certain kind of way.

Restorative

[FishandChips]

What a clear and well-written article. And what a pleasant, unassuming statement from Dr Zhao:

"A non-Newtonian gravity theory is now fully specified on all scales by a smooth continuous function. It is ready for fellow scientists to falsify. It is time to keep an open mind for new fields predicted in our formula while we continue our search for Dark Matter particles."

Even if the theory turns out not to stand up, words like this take us back to what makes science interesting and important. That "falsify" is worlds away from the publicity hounds and egomaniacs who so often represent science to the lay reader.

Your history isn't quite right

[Flying pig]

In fact, from the point of view of generating a mathematical model of planetary orbits from observation it doesn't matter whether the Earth or the Sun is taken as the centre (especially since neither is correct.) The problem was not ad hoc explanations - it was that Aristotle had said that heavenly bodies moved in circles, the Church had bought into this, and in dealing with the Church (just like today with biology) scientists had to be careful. So in order to explain actual motions they used combinations of circles called epicycles. Nikolaus Kupfernigk claimed, over 500 years ago, that the epicycle model was simplified if the Sun was at the centre - but, as he was working to better observations that existed in the past, he actually needed more epicycles than earlier astronomers. It was not surprising that there was dispute over his findings.

It was Kepler who realised that ellipses could be the correct model for orbits, and even there, to try and keep the Church happy, he tried to fit the major and minor axes into the shapes of the "Platonic solids".

History suggests that the example you are quoting is the opposite of what you want to show. It is better to let scientists come up with initially ad hoc explanations because they lead to the truth. Making initial unscientific assumptions and treating them as dogma suppresses and delays progress. Scientists are ambitious and a good way to become important is to replace someone else's theory - so scientists can be relied on to do that. For every established Dark Matter theorist there are probably several PhD students who would love to annihilate Dark Matter.

The line of argument in the parent annoys me because it tries to suggest that scientists left to themselves will produce ridiculous non-explanatory theories and then cling to them forever. It's the anti-scientific agenda of the Creationists who want to discredit science. Creationists and their like want to confuse the public as to the explanatory status of different scientific theories so they can claim their snake oil is on an explanatory par with plate tectonics, quantum electrodynamics or evolutionary biology.

Neutrinos

[Detritus]

Although I share your skepticism about dark matter, I couldn't help thinking about the neutrino, a "hidden" particle that filled another gap in physics. It took 25 years for physicists to finally detect the neutrino.

and the "law" of gravity?

[FreeUser]

No, that's not what happens. Laws say what happens, theories say why and/or how it happens. Laws don't try to explain behaviour, they just state it. Hence the laws of thermodynamics are laws, while the theory of relativity is a theory and always will be.

And the law of gravity? Observations say what happens. Theories say why and/or how it happense. Laws are what we call theories we think will never be falsified, and it's probably a word that should be dropped from any kind of scientific discussion, since we all should have learned by now that even the most basic assumptions and most obvious conclusions drawn from the most irrefutable of observations have a way of requiring revision from time to time, as better observations are made (Newton couldn't look at gravitational motion, and we cannot yet see into the higher folded dimensions of string theory, assuming such in fact exist).

The "laws" of thermodynamics are as theoretical as relativity. Both have been observed, both are mathematically modelled to great precision, both make useful predictions, both are falsifiable, and no one outside of a few religious wackos expects either to be falsified. That doesn't mean they won't be.

Someday we might find conditions in which entropy in a closed system decreases (candidates for something like this include the time leading up to the big bang--if such is found to have existed--and certain theories of the internal workings of black holes, etc.). Not that I or anyone else realistically expects this (but then, who expected the anomalies that would lead to the dark matter/energy vs. non-newtonian gravity debate, either), but the "laws" of thermodynamics are as falsifiable as the theory of relativity and, as it turns out, the "law" of gravity.

Theories do have a habit of becoming "laws" when they are basically considered irrefutable. They shouldn't--we should probably refer to gravity as the theory of gravity, and the laws of thermodynamics as the theories of thermodynamics. It might stop the "big bang theory" and "theory of evolution" rhetorical nonsense we've all been subjected to by communications majors coasting through college with a "C" average only to become network anchors...and help all of us to think clearer. That having been said, I imagine my calls to refer to the laws of thermodynamics as the "theories of thermodynamics" would fall on my old physics professor's deaf ears. Most of us like keeping our language the way it is, no matter how cumbersome or confusing it becomes--but that's a rant for another day. :-)

Re:Confusing creationists

[jc42]

This would be God's Law:
            Thou shalt not kill...

That would be God's instruction to man as reported through the ages, by man, in the Bible and its ancestor documents.

It couldn't have been reported that way "through the ages", because before roughly 1000 years ago, the English language didn't exist, and nobody would have understood the words "Thou shalt not kill".

This is germane to the discussion, because it hinges on the exact meaning of the word that the KJV translated to English as "kill". The original text was in classical Hebrew, not English, and as with any translation, word meanings don't always line up exactly. This always leads to questions about the accuracy of a translation, since there are often alternate words possible that don't quite mean the same thing in the target language. And for a long-dead language, you really can't know all the possible meanings a word may have had to the original speakers.

There is consensus among biblical scholars that the passage was closer to "Don't murder". But that's also ambiguous in English, with many court cases depending on how the jury members interpret the word "murder" (and how they interpret the judge's instructions).

In any case, a claim that the English phrasing of a biblical passage was "as reported through the ages" is absurd. It can't even be close to true. Only a small minority of followers of the Jewish/Christian bible(s) have ever understood English.

Dark Matter is real, and here to stay

[Pausanias]

Dark Matter exists, and in my opinion it is here for good. The attempts to come up with alternative theories of gravity are quite noble, but they only work on certain scales, and the proponents of these theories sometimes neglect examples that invalidate their theory. It would be quite elegant to be able to account for dark matter via a modification of gravity alone, but I am afraid that it will not be possible.

One of the most compelling pieces of evidence for the existence of dark matter is the "bullet cluster of galaxies" discovered by Maxim Markevitch and collaborators. Their 2004 peer reviewed article shows a small cluster of galaxies passing through much more massive one. As the cluster passes through, its gas is stripped, but the dark matter stays behind, detected via weak gravitational lensing. This effect is impossible to reproduce using alternative theories of gravity, because there is a visible separation between the total mass peak and the observable mass peak.

There are dozens of other peer-reviewed articles that argue against these alternative theories of gravity. What about the cosmic microwave background? The CMB is one of the underpinnings of modern cosmology and basically made the big bang the widely accepted theory that it is today. This recent analysis of the CMB show that the kind of alternative gravity proposed here is strongly disfavored by the CMB spectrum, and that it would imply too high a neutrino mass.

I challenge you to look through the literature for yourself. Here is a list of papers discussing modified newtonian gravity and its derivatives... You will find that yes, these alternative theories do work quite well at describing the rotation curves of galaxies, as TFA suggest. But on larger scales, such as in cluster of galaxies and the cosmic microwave background, they seem to fail convincingly.