In 1916, Albert Einstein dared to declare that Isaac Newton was wrong. No, he said, gravity is not a mysterious force emanating from Earth.
[...] And while the genius mathematician referred to this perplexing notion as his theory of general relativity, a title that stuck, his peers called it "totally impractical and absurd," a title that didn't. Against all odds, Einstein's mind-numbing idea has yet to falter. Its premises remain true on both the smallest of scales and the incomprehensibly large. Experts have attempted to poke holes in them again, and again and again, but general relativity always prevails.
And on Wednesday, thanks to an ambitious satellite experiment, scientists announced that, yet again, general relativity has proven itself to be a fundamental truth of our universe. The team conducted what it calls the "most precise test" of one of general relativity's key aspects, named the weak-equivalence principle, with a mission dubbed Microscope.
[...] The weak-equivalence principle is a weird one.
It pretty much says all objects in a gravitational field must fall in the same way when no other force is acting on them -- I'm talking external interference like wind, a person kicking the object, another object bumping into it, you get the idea.
[...] The Microscope project sent a satellite into Earth's orbit that contained two objects: a platinum alloy and titanium alloy. "The selection was based on technology considerations," Rodrigues said, such as whether the materials were easy and feasible to make in a lab.
[...] If you're into the technicalities, the results of the experiment showed that the acceleration of one alloy's fall differed from the other by no more than one part in 10^15. A difference beyond this quantity, the researchers say, would mean the WEP is violated by our current understanding of Einstein's theory.
[...] In a way, general relativity theory's solidity is kind of a problem. That's because even though it's an essential blueprint for understanding our universe, it isn't the only blueprint.
We also have constructs like the standard model of particle physics, which explains how things such as atoms and bosons work, and quantum mechanics, which accounts for things like electromagnetism and the uncertainty of existence.
[...] Both of these concepts seem just as unbreakable as general relativity, yet aren't compatible with it. So… something must be wrong. And that something is preventing us from creating a unified story of the physical universe. [...]
But the bright side is that the vast majority of scientists consider all of these theories to be unfinished. Thus, if we can somehow find a way to finish them – locate a new coupling, for instance, as Rodrigues says, or identify a new particle to add to the standard model – that might lead us to the missing pieces of our universe's puzzle.
"It should be a revolution in physics," Rodrigues said, of breaking the WEP. "It will mean that we find a new force, or maybe a new particle like the graviton – it is the grail of the physicist."
(Score: 2) by MIRV888 on Saturday September 17 2022, @12:16AM
No one can defy gravity.
(Score: 2, Insightful) by Anonymous Coward on Saturday September 17 2022, @12:32AM (4 children)
If I'm reading this right, it's like a very sophisticated version
of the experiment where an astronaut drops a feather and a rock
on the Moon?
Platinum and aluminum have densities of 21.09 and 2.7 g/cm^3 respectively.
I'm guessing they machined both pieces to the same size to see
if the density would make a difference, all else being equal and they
found no difference within measurement error.
(Score: 3, Informative) by RS3 on Saturday September 17 2022, @01:36AM (3 children)
Sorry, TFS says: "two objects: a platinum alloy and titanium alloy".
(Score: 1, Insightful) by Anonymous Coward on Saturday September 17 2022, @05:08AM (2 children)
I have no idea why my brain did that. Perhaps because titanium and aluminum are both used in aircraft. Stupid brain.
(Score: 2) by RS3 on Saturday September 17 2022, @12:48PM (1 child)
Perhaps you're human? :)
Or, maybe, bots are programmed to make random mistakes so we humans think you're human? :)
Titanium and aluminum are both used in bicycles and I'm not sure which is better for frames.
(Score: 2) by krishnoid on Saturday September 17 2022, @08:56PM
Or bots, for that matter :-)
(Score: 5, Insightful) by darkfeline on Saturday September 17 2022, @12:44AM (9 children)
Unfortunately, GR already failed the "dark matter" test; namely, do you have to add arbitrary padding scalars to your equations to make them balance and match experimentally observed values?
This is not to dismiss Einstein's contributions, he is undoubtedly a genius who has advanced human knowledge. But we know that there's something wrong with GR.
Join the SDF Public Access UNIX System today!
(Score: 5, Informative) by Gaaark on Saturday September 17 2022, @01:28AM (4 children)
Just like Newton passed for, what, a few centuries, now GR is passing... but it's only a close approximate like Newtonian Gravity.
It's not the answer yet, but everyone treats GR as if it is Gods word and so we have that non-scientific Dark Matter.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 5, Insightful) by acid andy on Saturday September 17 2022, @02:30AM (2 children)
It makes me wonder if the true physics could have infinite complexity. I suppose once you have a theory that would never be falsified even if you observed every object in the universe over all time, you still won't be able to tell if it's really exactly right or not, but no-one will care anymore (well, almost [wikipedia.org] no-one [wikipedia.org]). There are limits to the precision of our measurements due to quantum effects so presumably there's a limit to how accurate our predictions will ever need to be.
Master of the science of the art of the science of art.
(Score: 4, Interesting) by RS3 on Saturday September 17 2022, @01:06PM (1 child)
The word "atom" was coined because scientists thought they had isolated the thing that was the smallest most elementary particle that made up anything and everything.
Then they discovered electrons, protons, and neutrons.
When they smashed them apart and found quarks, leptons, bosons, muons, neutrinos, well: https://en.wikipedia.org/wiki/Subatomic_particle, [wikipedia.org] I started to figure that there's no end to finding what's inside of them. Kind of an infinite nested doll situation.
Especially when you think of mass / energy equivalence: what's the smallest measure of energy? Better: is there a smallest quantum of energy?
I'm pretty sure we can't ever measure it because of quantum limitations of our measurement systems.
Now my brain hurts and I'm hungry, what's for lunch? :)
(Score: 5, Informative) by Immerman on Saturday September 17 2022, @09:29PM
Hey now - the word atom was coined by ancient philosophers LONG before the discovery of what we now know as atoms. I was *used* for them because they initially seemed to fit the ancient philosophical concept. And is honestly a reasonable fit even now - it (roughly) marks the limit of where matter can be subdivided and remain matter in a conventional sense.
The ancients reasonably figured there were only two possibilities - either you could cut matter up smaller and smaller forever, or eventually you reached a point where you couldn't go any further. Instead we found that we reached a point where cutting it up further made it cease to behave in the ways we associate with matter, becoming complex wavefunctions instead.
(Score: 3, Interesting) by PiMuNu on Saturday September 17 2022, @04:50PM
If there was a theory that didn't invoke DM and could explain the features that are observed, I am sure folks would adopt it. No such theory exists.
Meanwhile, there exists a perfectly reasonable model which offends people on the internet because they want all matter to interact via electromagnetic force to satisfy some sort of strange prejudice against weakly-interacting (or - gasp - gravitationally-interacting only) matter.
(Score: 5, Interesting) by maxwell demon on Saturday September 17 2022, @06:20AM (3 children)
The dark matter distribution is not arbitrary. In particular, it still has to follow the laws of General Relativity. If it clearly didn't behave like matter should, nobody would consider dark matter to be matter.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 3, Insightful) by Immerman on Saturday September 17 2022, @09:08PM (2 children)
It is though - that's kind of the point. It has to be there in certain distributions for what we see to match the predictions of GR. But that's the *only* evidence we have for it - At present there's exactly as much evidence for dark matter as there is for invisible cosmic unicorns pulling stars around.
Which makes it equally possible that there's a flaw in GR at large scales. A possibility which becomes even more compelling given that at even larger scales we need to introduce a second, even larger arbitrary component - dark energy, to make GR predictions match with observations. Given the fact that despite half a century of searching we've still found no corroborating evidence that either exists, it doesn't look great for GR.
Plus there's that finicky fact that DM to visible matter ratios appear to be constant in virtually every galaxy we can see - a correlation that I haven't even heard a credible speculative explanation for, and hints strongly that visible matter is in fact the only gravitational source and it's GR that needs to be modified.
(Score: 1, Interesting) by Anonymous Coward on Sunday September 18 2022, @02:31AM
I think it is quite the opposite, that the ratios are all over the place. You have some that have very little DM [wikipedia.org] and some with quite a lot [space.com].
(Score: 4, Interesting) by maxwell demon on Sunday September 18 2022, @06:34AM
That's not true. For cosmic unicorns pushing stars around, we would not have any constraints that we could put into our equations to test the hypothesis. For dark matter we do, and dark matter passes those tests.
Also note that dark matter is not just about galaxy rotation curves. [medium.com]
Of course that's possible. But that's a very different claim than your original one: “GR already failed the "dark matter" test”. Dark matter is possible, and at the moment it's the more plausible explanation. There's simply no known modification of GR that explains all observations that are explained by dark matter.
Also note that those same evidences had led to the prediction that there's twice as much ordinary matter in the universe than we had observed until then, and indeed that ordinary matter has been found. [soylentnews.org] That is evidence for the correctness of the models, and thus also evidence for dark matter.
To that, you've already gotten an answer from AC. Now many galaxies do have similar ratios, but then, if they formed under similar circumstances, that is to be expected. But the fact that dark matter content does differ in different galaxies is again a strong argument in favour of dark matter.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 3, Interesting) by dltaylor on Saturday September 17 2022, @08:28PM (1 child)
The standard model explains nothing, it is just bookkeeping. This is rather like the early days of the periodic table, where new elements were predicted because there was a gap in the table.
The "why" of the various arbitrary constants is always "because it makes the bookkeeping balance". Mass/energy of products don't quite work? Add another particle or field. It's how we got from indivisible atoms to nuclei and electrons, and why we needed neutrinos to exist.
When particle physicists can actually detail why the charge of an electron or positron are 3x (or 3/2) the charge of a quark, other than "it works", or why the supersymmetric partners of electrons (...) have those exact values, then they will be "explaining". Standard model fans whine about the string theorists arbitrary constants, but the entire standard model is nothing but a collection of such.
I'm not saying the work has no value, but currently they're still exploring the beastiary, rather than delving into paleogenetics to see from whence we got camelids in Peru and what we call "camels" of more than one flavor in Africa and Asia.
(Score: 3, Interesting) by hendrikboom on Monday September 19 2022, @01:59AM
See The Algebra of Grand Unified Theories [wordpress.com] for a delightful discussion about how properties of the various fermions can be obtained from the SU(5) symmetry group.
The link shows the way to both a long youtube video and a published paper. Fascinating stuff.
We're not all the way there, but we're a long way from being clueless.