Einstein equations don't work at large scale?

[gen x]

Below short video explain that Einstein equations don't work at large scale and dark matter/energy are just "fix" to make equations try to work. I also know that Einstein theory dont fit in quantum world.

I am interested what are the consequences that theory not works in large and micro scale, does it mean that fundament of theory is maybe wrong so we need new theory of gravity or that theory need just little correction ?

<Instagram video removed by moderator>

 

[Dale]

Below short video

This source does not meet the PF standards. So we can certainly discuss your questions, but we will not be relying on or discussing the source itself.

Einstein equations don't work at large scale and dark matter/energy are just "fix" to make equations try to work.

I agree with this statement regarding dark matter, but not dark energy. Dark energy is the cosmological constant, which is a fully legitimate free parameter of the theory itself.

I am interested what are the consequences that theory not works in large and micro scale, does it mean that fundament of theory is maybe wrong so we need new theory of gravity or that theory need just little correction ?

This is not an uncommon situation in science. It can go either way. Historically, slight deviations in Saturn’s orbit led scientists to propose the existence of additional planets that had not been observed. Eventually with improvements in their telescopes they were able to observe Neptune and Uranus. Slight deviations in Mercury’s orbit led scientists to propose the existence of another planets closer to the sun. Despite improvements in telescopes it was never found. When GR was developed it explained the slight deviations in the orbit of Mercury.

So two very similar deviations from the theory. One led to the discovery of new sources. The other led to discovery of new physical laws.

At this point dark matter could go either way. We have neither observed dark matter nor invented a suitable new theory. But work is proceeding on both fronts.

 

[Ibix]

Back in 1780, it was discovered that Newtonian gravity did not correctly predict the positions of the outer planets. Herschel proposed a previously unknown planet, backed its location out of the maths, and discovered Uranus. If social media had been a thing at the time, it would have been awash with armchair scientists (and legit ones pushing their own theories, to be fair) saying what an idiot Herschel was trying to prop up an obviously dead theory by proposing a new planet. They'd have been wrong.

(Edit: I see I've confused my history of the outer planets. Uranus seems to have been discovered just by improved observational techniques. Neptune, however, was identified from anomalies in Uranus' observed orbit compared to prediction and then sighted based on the orbit of an unknown planet required to correct those anomalies.)

They'd have been right in the late 1890s about the failure of Newton to correctly predict the position of Mercury - we needed GR for that.

Social media wasn't yet called that but did kind of exist in the 1990s/2000s when the so-called Pioneer Anomaly was unexplained, and it did have many people arguing that this was definitely a failure of gravitational theory. It turned out to be a modelling oversight - a totally mundane but subtle interaction between the power supply and antenna that nobody had thought to include in the model.

I don't think we should rule out any of these three possibilities with respect to the dark sector. It could be evidence of GR failing (as MOND advocates would say). It could be evidence of new forms of "stuff" that we haven't yet seen elsewhere (the mainstream view). It could be a failure to model correctly (as Deur says, for example). I can't see the video, but if it's taking the view that GR is definitely wrong because of dark energy/matter then I would say it's stuck its neck out a long way at this point.

 

[Dale]

I don't think we should rule out any of these three possibilities with respect to the dark sector. It could be evidence of GR failing (as MOND advocates would say). It could be evidence of new forms of "stuff" that we haven't yet seen elsewhere (the mainstream view)

And indeed this is the current situation. We are currently working along both paths.

 

[Ibix]

And indeed this is the current situation. We are currently working along both paths.

I see we said much the same things!

 

[gen x]

And indeed this is the current situation. We are currently working along both paths.

Today we know that Newton mechanics is wrong(even it is enough accurate for every day life for low speeds...)
So there is possibility one day we will find that time and space are absolute instead relative and there is no space-time curvature and something else cause gravity?

 

[Dale]

So there is possibility one day we will find that time and space are absolute instead relative and there is no space-time curvature and something else cause gravity?

That is certainly a possibility. It is under investigation.

However, even if it turns out to be true, relativity and spacetime curvature will still be taught in schools. Just like Newtonian gravity is still taught in schools.

 

[gen x]

@Dale
@Ibix

I would like that some day it turns out that time is absolute, it better suit human intuition.

If time is relative as we learn today, universe is old 13.8 billions years, looking from witch frame if absolute frame at rest dont exist?

So universe age is different from different places in space?

 

[Ibix]

If time is relative as we learn today, universe is old 13.8 billions years, looking from witch frame if absolute frame at rest dont exist?

The frame that sees the Cosmic Microwave Background as uniform. This is the nearest thing to "on average at rest with respect to matter in the universe" that there is.

So universe age is different from different places in space?

If you define space as the uniform CMB rest frame then the universe is the same age at all places and this is tautologically true. If you define space a different way then the universe is a different age at different places and again this is tautologically true.

Cosmologists always use the same definition of space (CMB rest frame) because the maths is easiest using that definition. So the age of the universe is stated with that definition with little acknowledgement, basically for the same reason road signs state the speed limit as 30mph without specifying "with respect to the Earth's surface". Strictly, the "with respect to" should always be supplied, but in practice it usually isn't unless it differs from the usual answer.

 

[Ibix]

I would like that some day it turns out that time is absolute, it better suit human intuition.

If the history of science has taught us one thing, it's that human intuition is a very poor guide to how the world actually works.

 

[Dale]

I would like that some day it turns out that time is absolute, it better suit human intuition.

The interesting thing about intuition is that it is not fixed. Intuition is built on experience. At this point I have enough experience with relativity that I find it pretty much as intuitive as Newtonian mechanics. The actual laws of physics cannot be changed by intuition, but intuition can be built around the actual laws of physic.

I think it is important to note that this has already happened. In Aristotle's day the intuitive physics was that forces produced velocity, not acceleration. Newton's assertion that forces produce acceleration was unintuitive. That has changed. Students now find Newton's laws intuitive. And despite the fact that Newton's laws have been demonstrated to be incorrect, they are still taught in schools, and the previously unintuitive portion specifically still remains valid and has become intuitive.

I would expect the future to mirror this. I would expect that future students will consider relativity's non-absolute time to be intuitive, and that it will continue to be used even after relativity has been supplanted by some future theory. I would not count on a future theory to rescue an old intuition.

 

[PeterDonis]

Einstein equations don't work at large scale

More precisely, if we just use the matter we can actually see as the source in the Einstein Field Equation, the model does not match the data.

dark matter/energy are just "fix" to make equations try to work

More precisely, they are additional things we add to the source, over and above the matter we can actually see, in order to make the model fit the data.

Describing this as the Einstein Field Equation "not working", however, is not correct. The source is a free parameter in the equation. Adjusting free parameters in a model to get a best fit to the data is something that is done all the time in science. It doesn't mean the equations don't work.

What we are missing is an understanding of what kind of "stuff" dark matter and dark energy are, i.e., where they would fit in the other equations we have for describing matter and energy--not the Einstein Field Equation, but things like the Standard Model of particle physics, which does not contain anything that would account for dark matter or dark energy.

(Note that "dark energy", if it is in fact just a cosmological constant, i.e., an intrinsic property of spacetime, does fit into the Einstein Field Equation without needing to modify the source, i.e., the stress-energy tensor, at least according to the modern view of how that equation is to be derived from an underlying Lagrangian.)

 

[PeterDonis]

Today we know that Newton mechanics is wrong

Not "wrong", no. It is a valid approximation to GR in the regime where gravity is weak and all relative speeds are small compared to the speed of light.

So there is possibility one day we will find that time and space are absolute instead relative and there is no space-time curvature and something else cause gravity?

In the sense that we might find some other underlying theory that has these properties, yes.

But GR (and a fortiori Newtonian mechanics) will still be a valid approximation to whatever underlying theory we might find, in the domain where we already know it works. So we will never find out that GR is "wrong". But we might find out that it is only an approximation to something else.

 

[Dale]

GR (and a fortiori Newtonian mechanics) will still be a valid approximation to whatever underlying theory we might find, in the domain where we already know it works

This is a very important point in understanding how science actually works. Popper popularized the idea of falsification, but verification is also important. Experiments verifying a theory do not disappear simply because another experiment falsified it.

 

[sbrothy]

@Dale
@Ibix

I would like that some day it turns out that time is absolute, it better suit human intuition.

If time is relative as we learn today, universe is old 13.8 billions years, looking from witch frame if absolute frame at rest dont exist?

So universe age is different from different places in space?

@Ibix beat me to it but yeah

High School Post in thread 'I don't understand the Michelson–Morley experiment'

Yesterday, 2:13 PM

That's why they repeated the experiment multiple times over the course of a year. We could have a zero velocity relative to a static ether at one instant, but not throughout the year.

No. Light coming from a source approaching you will have higher energy than light from an identical source moving away from you. This is one interpretation of kinematic red and blue shifts. Light from both sources will have the same speed, however.

Photons are entities in relativistic quantum field theory and they do not behave very much like a naive idea of a particle at all. Our general advice is that...

• sbrothy

EDIT: Yeah you gotta click the link to get my drift

 

[chwala]

Am Totally lost here! Am in the dark!

In simple straightforward terms, are you guys saying Newton's laws are wrong? Also theory on relativity?wrong? ... then what else could be wrong in science!


...plus I've always asked myself, this constant g=9.81... , how did that come into existence, I understand the pull is different at different points on earth's surface, but who determined and ascertained this value to hold as true.

 

[PeterDonis]

are you guys saying Newton's laws are wrong?

No. See post #13.

who determined and ascertained this value to hold as true.

The laws of physics plus the particular configuration of matter in the Earth.

 

[Dale]

In simple straightforward terms, are you guys saying Newton's laws are wrong?

I don’t think there is an answer that is both simple and complete.

Newton’s laws have been experimentally shown to be correct in the classical limit.

If you consider Newtonian space and time to be part of Newton’s laws then that has been experimentally shown to be incorrect at high speeds. But Newton’s 2nd law can be rewritten in a way that is correct at high speeds.

If you consider Newtonian gravity to be part of Newton’s laws then that has been shown to be incorrect in strong gravitational fields. But the concept of curved spacetime for gravity comes from taking Newton’s 1st law seriously.

If you consider forces to only act on matter then Newton’s 3rd law had been shown to be incorrect in electromagnetism. But Newton’s 3rd law is the mechanical expression of the conservation of momentum, which applies to electromagnetism.

So Newton’s laws have a domain of applicability, the classical domain. Inside that domain they are experimentally validated. Outside that domain they are experimentally falsified, and other laws are experimentally validated. Newton’s laws are the classical limit of those other laws, meaning that it is part of them.