Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Newton's law of gravity passes its biggest test

science.org

Post reply on HN
Print view View original

21–30 of 162 posts

Re: Newton's law of gravity passes its biggest test

#21

Post by adgjlsfhk1 »

PaulHoule wrote: post #4
GuB-42 wrote: post #2

If you follow Sabine Hossenfelder's channel, she has a MONDOmeter. With MOND (modified Newtonian gravity) on one side and dark matter on the other side. As new papers come out the needle goes back and forth, and I guess that she will make a new video if she hasn't already, with the needle moving one step towards dark matter. I find it interesting how it doesn't seem to settle. Dark matter is still the favorite, but t…

MOND does amazingly well at galactic rotation curves, less well at anything else. If you think it started with Vera Rubin in 1966 MOND seems natural, but if you know that it started with Fritz Zwicky in 1933 than dark matter is easier to believe.

MOND only really does well on galactic rotation curves because it has free parameters that are tuned to "predict" the correct answer for galactic rotation curves.

Re: Newton's law of gravity passes its biggest test

#22

Post by rhdunn »

Lvl999Noob wrote: post #7

I thought newtonian gravity was already proven to be inaccurate with Einstein's Special Relativity (or General Relativity?) giving better results on cosmic scales (basically analogous to an approximation vs an exact formula)?

Special Relativity is an extension of Galilean/Newtonian mechanics (motion of projectiles and other objects) to the case where the object is travelling at speeds that are a fraction of the speed of light. It deals with non-accelerating frames of reference. Satelites need to use this to correct for time dilation effects, but tracking the trajectory of an arrow/etc. or a car/etc. travelling from one location to another then classical mechanics is sufficient.

General Relativity is an extension of Newtonian gravity. It is also an extension of Special Relativity to cover accelerating frames of reference. Satelites need to use this, as does tracking the orbit of Mercury. However, for the orbits of other planets and the moon, using Newtonian gravity is sufficient for a reasonable degree of accuracy, and is used for tracking things like equinoxes/solstices, full moons, etc..

Re: Newton's law of gravity passes its biggest test

#24

Post by stronglikedan »

cwmma wrote: post #13
GuB-42 wrote: post #2

If you follow Sabine Hossenfelder's channel, she has a MONDOmeter. With MOND (modified Newtonian gravity) on one side and dark matter on the other side. As new papers come out the needle goes back and forth, and I guess that she will make a new video if she hasn't already, with the needle moving one step towards dark matter. I find it interesting how it doesn't seem to settle. Dark matter is still the favorite, but t…

my understanding is that there are a few MOND champions who are still holding on to the idea while everyone else has moved on.

so MOND is the new String Theory...

Re: Newton's law of gravity passes its biggest test

#25

Post by pfdietz »

stronglikedan wrote: post #24
cwmma wrote: post #13

Earlier quoted context omitted.

my understanding is that there are a few MOND champions who are still holding on to the idea while everyone else has moved on.

so MOND is the new String Theory...

It never had the institutional imprimatur of string theory.

Re: Newton's law of gravity passes its biggest test

#26

Post by gus_massa »

cowl wrote: post #18
GuB-42 wrote: post #2

If you follow Sabine Hossenfelder's channel, she has a MONDOmeter. With MOND (modified Newtonian gravity) on one side and dark matter on the other side. As new papers come out the needle goes back and forth, and I guess that she will make a new video if she hasn't already, with the needle moving one step towards dark matter. I find it interesting how it doesn't seem to settle. Dark matter is still the favorite, but t…

It's funny how for MOND we cant accept that it has some unknowns yet but we are more than willing to accept the FULL UNKNOWN Dark Matter. it's easy. put "Dark" in front of something and you don't have to explain it at all, no matter that something else explains at least 60-70% instead of 0.

We make a similar guess for the stuff that is in the center of Earth. We measure local gravity and speed of sound velocity, and we guess here is liquid, here is solid, here is this rock, here is this another rock [1]. See for example https://www.livescience.com/64943-nobody-understands-the-gia... nobody has seen them, we guess they are there.

Dark matter is another guess. We guess there is more matter in galaxies than what the telescopes show. We can compare the amount of mater guessed from galaxy rotation with other measurements. In this case they compare it with the gravity between a few galaxies.

Nobody is happy that we don't know what dark mater is. There are a few theories, but none of them has enough experimental support. More lack of confirmed details in https://en.wikipedia.org/wiki/Dark_matter#Composition

[1] I don't know enough about rocks https://xkcd.com/2501/

Re: Newton's law of gravity passes its biggest test

#27

Post by layer8 »

stronglikedan wrote: post #24
cwmma wrote: post #13

Earlier quoted context omitted.

my understanding is that there are a few MOND champions who are still holding on to the idea while everyone else has moved on.

so MOND is the new String Theory...

String theory is still the leading contender for quantum gravity.

Re: Newton's law of gravity passes its biggest test

#28

Post by cowl »

gus_massa wrote: post #26
cowl wrote: post #18

Earlier quoted context omitted.

It's funny how for MOND we cant accept that it has some unknowns yet but we are more than willing to accept the FULL UNKNOWN Dark Matter. it's easy. put "Dark" in front of something and you don't have to explain it at all, no matter that something else explains at least 60-70% instead of 0.

We make a similar guess for the stuff that is in the center of Earth. We measure local gravity and speed of sound velocity, and we guess here is liquid, here is solid, here is this rock, here is this another rock [1]. See for example https://www.livescience.com/64943-nobody-understands-the-gia... nobody has seen them, we guess they are there. Dark matter is another guess. We guess there is more matter in galaxies tha…

Dark matter is not another Guess. is no guess at all. its the same as saying the center of the earth is made of Dark Core. and when someone proposed liquid core, there would be papers how a liquid core doesnt explain 100 %, and neither does rock or solid so Dark Core it is because it's sIMpLer to have just one Dark Something than 3 different somethings to explain anything.

The fact that there are tentatives to identify what it might be does not ammegliorate the fact that at it's core (pun intented) Dark matter is something to make equations fit without any other thought behind it or whether there might be several things behind it or god forbid that we juddge the equations themselves. I mean we got relativity because of a minor discord with newtonian Laws. (the orbit of Mercury). just a tiny percentage of obeservable behaviour at that time but it was a different time. a time where you could bring down the existing science of the day for a tiny percentage and now we accept 90% observation disaccordance (dark energy+dark matter) with what the equation require.

Re: Newton's law of gravity passes its biggest test

#29

Post by wongarsu »

fooker wrote: post #19
GuB-42 wrote: post #2

If you follow Sabine Hossenfelder's channel, she has a MONDOmeter. With MOND (modified Newtonian gravity) on one side and dark matter on the other side. As new papers come out the needle goes back and forth, and I guess that she will make a new video if she hasn't already, with the needle moving one step towards dark matter. I find it interesting how it doesn't seem to settle. Dark matter is still the favorite, but t…

We are likely going to find out that both are unfixably faulty. It'll take either the next Einstein or some groundbreaking experimental observation to get there in my opinion. If it was possible to incrementally fix these theories, the army of postdocs working on these would have already done so in the last decade or so.

But at least the experimental results disproving these incremental fixes should be exactly the kind of thing the next Einstein should need for coming up with an entirely new way of looking at things

Re: Newton's law of gravity passes its biggest test

#30

Post by fooker »

wongarsu wrote: post #29
fooker wrote: post #19

Earlier quoted context omitted.

We are likely going to find out that both are unfixably faulty. It'll take either the next Einstein or some groundbreaking experimental observation to get there in my opinion. If it was possible to incrementally fix these theories, the army of postdocs working on these would have already done so in the last decade or so.

But at least the experimental results disproving these incremental fixes should be exactly the kind of thing the next Einstein should need for coming up with an entirely new way of looking at things

Interestingly, more often than not it happens the other way.

Some once-in-a-generation scientist has an intuition that turns out to be true and mathematically elegant.

It gets proven experimentally years or decades later.

Relativity was exactly like this.

Post reply on HN