How does gravity work?

How does science work? And what's all this about quantum mechanics?

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Wyman
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Re: How does gravity work?

Post by Wyman »

wtf wrote:
Wyman wrote:I remember watching a video of a Feinman lecture ...
Thanks Weiman.
Feynman. But you're still 0 for 12 or so on substance.
uwot
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Re: How does gravity work?

Post by uwot »

Wyman wrote:My comment was directed at the other guy - wtf. Sorry I wasn't clear.
Actually, on reflection, it is fairly clear who you were addressing, so I'm sorry I didn't read with more care.
Wyman wrote:I have a question. You talk of a mathematical model of a physical model of the universe. Why two models? Why not just a mathematical model?
This relates to what I said about general relativity above. Einstein did a lot of his best work by exploring the consequences of thought experiments. For example one of the questions he asked was if you were travelling at the speed of light, and you held a mirror in front of you, what would happen to your reflection? Intuitively the answer is that it would disappear, because the light couldn't reach the mirror to be reflected. Einstein didn't like that idea, so he slowed down time, squeezed space together and came up with special relativity. A lot of the mathematical modelling had been done a few years earlier by Hendrik Lorentz and the mathematical model of 4D spacetime was developed by Herman Minkowski.
When Einstein turned his thoughts to gravity, he came up with the physical model of spacetime as a substance that could be stretched and squeezed; no doubt you have seen the analogy of a rubber sheet.
Wyman wrote:I remember watching a video of a Feinman lecture about models. He presented two models of gravity in which the maths were the same. He basically said that the physical models were merely psychological tools for solving problems.
The idea that time is a substance that can be slowed down, or that space can be stretched or warped are psychological tools that help make sense of the maths, but the fact that the maths is so successful leads some physicists to believe their psychological tools are real, much as people believed the experimentally successful Ptolemaic geocentric universe was real. The fact is, you can make up any psychological tool you like that is consistent with the maths, so there could be several physical models that will do.
So to answer your question, the mathematical model is all you need to do physics and to some physicists, physical models are just philosophy.
Wyman wrote:He distinguished two philosophies towards models - the Greek, which is deductive; and the Babylonian, which is ad hoc - bits of model here and there, changing from one to another as the need arises. He advocated for the latter, claiming the Greek philosophy is artificially limiting.

The Babylonian model is closer to the actual state of physics. Some physicists fret over the fact that relativity and quantum mechanics are based on different models, some are happy to hop from one to the other, and some see it as a challenge to come up with a single model that incorporates both.
Wyman wrote:Interesting lecture, it's on youtube.
Richard Feynman is always worth watching.
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attofishpi
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Re: How does gravity work?

Post by attofishpi »

uwot wrote: How does gravity work?
Gravity exists because of the Higgs field.
wtf
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Re: How does gravity work?

Post by wtf »

attofishpi wrote:
Gravity exists because of the Higgs field.
Is that a fact about the universe? Or a fact about the model? Since our idea of gravity has gone from Aristotle to Newton to Einstein to Higgs, why shouldn't there be an even better idea next century?

A statement like "Gravity exists because of the Higgs field" seems to me to confuse the map with the territory.

Uwot made this point at length in his previous post.
uwot wrote: The idea that time is a substance that can be slowed down, or that space can be stretched or warped are psychological tools that help make sense of the maths, but the fact that the maths is so successful leads some physicists to believe their psychological tools are real, much as people believed the experimentally successful Ptolemaic geocentric universe was real. The fact is, you can make up any psychological tool you like that is consistent with the maths, so there could be several physical models that will do.
So to answer your question, the mathematical model is all you need to do physics and to some physicists, physical models are just philosophy.
So is there "really" a Higgs field? Well, there turned out NOT to be an invisible Newtonian force acting at a distance. What makes us think there is a Higgs field; as opposed to the Higgs field being merely the name of the latest mathematical model that works, along with a convenient visualization? A field like the magnetic field that we can see when we pour little grains of metal on a piece of paper with a magnet underneath it like they showed us in school? Is there really a field? What is it, exactly, and why? It's bowling balls on rubber sheets again. Stories we tell ourselves to help us visualize the latest mathematical formalism that fits the experiments.

I think this is the point Uwot is making, and if I'm misunderstanding Uwot I apologise. But it's certainly the point that I'm making. Higgs is a story we tell ourselves. Nobody really knows why stuff falls down.
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attofishpi
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Re: How does gravity work?

Post by attofishpi »

wtf wrote:
attofishpi wrote:
Gravity exists because of the Higgs field.
Is that a fact about the universe? Or a fact about the model? Since our idea of gravity has gone from Aristotle to Newton to Einstein to Higgs, why shouldn't there be an even better idea next century?

A statement like "Gravity exists because of the Higgs field" seems to me to confuse the map with the territory.
As i stated earlier, i watched Sean M. Carrol explain the recently proven higgs particle.
It seemed apparent that this Higgs particle playes a crucial role in causing SOME other particles to be affected by some sort of soup - the field, and hence causing them to be susceptible to display the characteristics of mass - in fact the cause of gravity.

I've been trying to find the video, if i do i will post it. But it seems that at these sub atomic scales, that yes there is a field - the Higgs field that causes SOME of these sub atom particles to be susceptible to mass, hence gravity.
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Re: How does gravity work?

Post by wtf »

attofishpi wrote:
I've been trying to find the video, if i do i will post it. But it seems that at these sub atomic scales, that yes there is a field - the Higgs field that causes SOME of these sub atom particles to be susceptible to mass, hence gravity.
Suppose you had been living in the time of Newton, and you attended a brilliant lecture describing gravity as an invisible force between massive objects. Would you say, "But it seems that at these sub atomic scales, that yes there is a force -- the Newtonian force -- that DOES cause matter to attract other matter in proportion to the product of their masses and inversely proportional to their distance."

Would you say that? Or, with the hindsight we have today, would you recognize that as a description of a MODEL of reality but not ultimate reality itself?

If the latter, can you see that a hundred or five hundred years from now we'll see the Higgs the same way? As a great approximation for its time, but not literally true?

Can you see that? Or do you think that this year, of all the years in human history, we are in possession of the ultimate truth about gravity?
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attofishpi
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Re: How does gravity work?

Post by attofishpi »

wtf wrote:
attofishpi wrote:
I've been trying to find the video, if i do i will post it. But it seems that at these sub atomic scales, that yes there is a field - the Higgs field that causes SOME of these sub atom particles to be susceptible to mass, hence gravity.
Suppose you had been living in the time of Newton, and you attended a brilliant lecture describing gravity as an invisible force between massive objects. Would you say, "But it seems that at these sub atomic scales, that yes there is a force -- the Newtonian force -- that DOES cause matter to attract other matter in proportion to the product of their masses and inversely proportional to their distance."

Would you say that? Or, with the hindsight we have today, would you recognize that as a description of a MODEL of reality but not ultimate reality itself?

If the latter, can you see that a hundred or five hundred years from now we'll see the Higgs the same way? As a great approximation for its time, but not literally true?

Can you see that? Or do you think that this year, of all the years in human history, we are in possession of the ultimate truth about gravity?
Lots and lots of questions here. I think that when talking about the Newtonian model of gravity Newton gave us a great understanding of how mass and distance played in effect of their relative distances when it comes to objects we can hold and throw and bounce.
But now we are comprehending matter at subatomic levels and this is where things really need to be understood. That some particles exhibit no mass, and others DO. And its these particles that DO that are the ones that the Higgs field are having an effect on.

And to add - no im not sure the Higgs is the ultimate truth to gravity - im just a laymen who the fuck am i to make such a decision!! :D
wtf
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Re: How does gravity work?

Post by wtf »

attofishpi wrote: And to add - no im not sure the Higgs is the ultimate truth to gravity - im just a laymen who the fuck am i to make such a decision!! :D
Now we're getting somewhere. Me too. My only point is that ALL science is model building and so far we have never gotten to "ultimate" reality. If we imagine ourselves a hundred or five hundred years from now, it's likely that our current theories will be seen as no more than the best approximation we were capable of.

Of course Higgs and all our current theories are amazing and worthy of study. We just have to guard against imagining that we are doing anything other than building models of a reality that we may never fully understand. Can an ant on a leaf ever understand the tree? Personally I don't think so.

I'm talking philosophy of physics, not physics itself. Hope that's clear. And if you do find that Higgs video, I'd love to see it!
uwot
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Re: How does gravity work?

Post by uwot »

wtf wrote:Suppose you had been living in the time of Newton, and you attended a brilliant lecture describing gravity as an invisible force between massive objects. Would you say, "But it seems that at these sub atomic scales, that yes there is a force -- the Newtonian force -- that DOES cause matter to attract other matter in proportion to the product of their masses and inversely proportional to their distance."
This was a pivotal moment in history and, more than any other, marks the separation of physics and philosophy. What you would have heard in a brilliant lecture on gravity, would have depended on which side of the English Channel you had been. In Britain you would probably have been listening to a Newtonian explaining the inverse square law, a strictly mathematical description. Had you stuck up your hand and asked how it actually works, the answer would have been, effectively, don't know, don't care. On the continent, it is more likely that you would have been listening to a Cartesian, Gottfried Leibniz for example, giving an account of the vortex theory of gravity, according to which space is made of tiny bits of matter which are swept around the sun, a bit like water going down the plughole, with the Earth as a rubber duck being dragged around with it.
Both Descartes and Leibniz were mathematicians of the first rank, it is Cartesian coordinates which are most commonly used in geometry, and Leibniz's notation that is used in calculus, but to them, how things work mattered. It is no accident that in the English speaking world that they are remembered primarily as philosophers; the point being that their physical, philosophical hypothesis makes no difference to the fact that Newton's mathematical description of this mysterious force works.
wtf wrote:Would you say that? Or, with the hindsight we have today, would you recognize that as a description of a MODEL of reality but not ultimate reality itself?

If the latter, can you see that a hundred or five hundred years from now we'll see the Higgs the same way? As a great approximation for its time, but not literally true?
The Higgs field is, in effect, a refinement of the vortex hypothesis, at least insofar as it is a philosophical account of what creates mass; which as Noax alludes to, in this instance is synonymous with inertia. Basically, the Higgs field is some hypothetical 'stuff' with mechanical properties. What makes it physics is that there is a mathematical treatment which predicts that if you hit the field hard enough, you will create a ripple with specific properties called the Higgs boson. What the LHC has discovered is a ripple that looks very like the one predicted. There is no reason to think that in 500 years time, smashing hadrons together won't produce the same ripples. Whether our descendants attribute it to the Higgs field is a different matter.
wtf wrote:Can you see that? Or do you think that this year, of all the years in human history, we are in possession of the ultimate truth about gravity?
Well, then you get into underdetermination. We might actually be in possession of the ultimate truth, but there is no way of knowing what future experiments will uncover.
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SpheresOfBalance
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Re: How does gravity work?

Post by SpheresOfBalance »

uwot wrote:
SpheresOfBalance wrote:Lift is created because of the air foil design...
Absolutely true, but will an aeroplane take off if it doesn't divert a whole load of air downwards by lifting it's nose?
I have you at a disadvantage uwot, because I was flyer. All that I wrote above was not something from a book that I referenced yesterday. It was from the memory of my training in 1975 & 1982 and my subsequent 2000 hours of flying aboard a Lockheed Orion P3-C as an Aviation Antisubmarine Warfare Equipment Operator where I talked daily with pilots in the cockpit, even being allowed to control the multi-million dollar beast of a bird for a moment or two. For 14 years I worked in, on, and around, multimillion dollar aircraft. One of the aspects of my job was considered, "safety of flight." At least my pilots loved me, though I couldn't say that of my tacco, (I was better at flying than killing) ;-).

So no, the thrust/pull of the engines in fact propel the craft through the air. The faster the chambered air foil goes through the air, all control surfaces in their neutral position, the faster the craft will tend to rise. As a matter of fact I have a video shot by me in the cockpit, of my pilots saying the magic word, "rotate," which meant the aircraft was moving through the air fast enough to achieve lift sufficient to overcome it's weight, so to then pull back on the yoke thus forcing the elevator up, so as to force air up, thus the tail down, pivoting on the main landing gear, lifting the nose gear off the ground and increasing the wing's (airfoil's) angle of attack relative to the earths surface, thus increasing the air pressure on the bottom of the wing relative to the top, but no air is pushed down except for that emanating from the engines exhaust ports and even that's not really down, slightly maybe.

Only VTOL fixed wing aircraft push air down perpendicular to the earths surface, and that's via their rotating exhaust ports. Their initial lift, only during takeoff (and final during landing), is 100% thrust directed at the surface of the earth, gradually directing it more and more towards the rear thus slowly creating forward momentum until they can say, "rotate," thus signifying that the airfoils movement through the air is sufficient to create lift greater than their weight, at which time the exhaust ports are pushing gases mostly parallel to the earths surface.

No air is pushed down on conventional fixed wing aircraft, it's all to do with variable air pressure, which of course the wings angle of attack increases. Of course forward momentum through the air mass can't be overlooked as a means to create that difference in air pressure. When they test new airframe/wing designs they do so in a wind tunnel so as to emulate variable forward thrust through an air mass.

It's a combination of thrust and lift (which is air pressure differential due to shape and angle of attack).
The wing is not pushing air down, the air is pushing the wing up.
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Re: How does gravity work?

Post by wtf »

SpheresOfBalance wrote: I have you at a disadvantage uwot, because I was flyer.
Just wanted to mention that this doesn't give you as much credibility as you'd think.

Back in the day I was a recreational sailor. As you know, a sailboat can sail upwind by sailing at an angle to the direction of the wind and obtaining lift from a combination of the Bernoulli effect on the curved sail acting against the counterforce on the keel. The lift generated by the sail works just like an airplane wing.

Except there's a problem. Sails are effectively two-dimensional while airplane wings are three-dimensional. Wings have thickness, sails don't. So there is something wrong with the fables told to sailors. Sailors don't actually know what propels sailboats upwind. They only know the story they've been told.

I'm not saying you are not an expert in the physics of flight. Only that being a sailor doesn't give you access to inside information about what propels sailboats. It only provides access to the FABLES they tell sailors about what propels sailboats. I assume the same may true about pilots.

So if you have some actual knowledge about the physics of flight, I'll happily agree that you know about it. But if you are only repeating the stories they tell you in flight school, well those may be physics or just physics fables. Bowling balls on rubber sheets again. Very important to distinguish three levels: Actual reality, scientific models, and popularized fables.
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Re: How does gravity work?

Post by Noax »

SpheresOfBalance wrote:The wing is not pushing air down, the air is pushing the wing up.
This statement is a violation of Newton's third law. Something must be pushed down to drive a heavier-than-air object aloft. Nose tilts up, the wing angle of attack pushes air down the same way it does with a ceiling fan. In level flight, there is a net downward thrust to the air which is planely (pun intended obviously) evident if the aircraft is flying through a medium (100% humid air for instance) in which its wake becomes visible.

I've been at the end of runways of large aircraft (8-engine B52) taking off. You can feel the pressure as they go over. Funny that they let you stand there, but not in the same place at a commercial airport.

Engines of most aircraft are there to overcome friction which is why they thrust forwards and not up, attack angles not withstanding. Many military aircraft have plenty to spare beyond that of course and some have enough to thrust straight up leaving the wings with about as much function as the fins on a rocket: steering but no lift.
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Re: How does gravity work?

Post by Cerveny »

uwot wrote: Sat Feb 25, 2017 9:03 pm
Cerveny wrote:- Can you name any (model)?
I think you mean test. Well, the detection of gravity waves by LIGO is one.
Cerveny wrote:- I only critize that GTR does not work with gravitational repulsion.
It's not that GR doesn't work with gravitational repulsion necessarily, there is clearly a phenomenon that is not predicted the theory. Nonetheless, GR still works very well on the scale that we can measure it under controlled conditions.
Cerveny wrote:I do not compare dark matter with antimatter.
Fair enough.
GTR works quite well, but it cannot explain "dark" matter and it cannot be quantized. And for example such shift of Mercury trace has been exactly (the same expression) computed by clasical way by, I think, Paul Gerber...
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Re: How does gravity work?

Post by thedoc »

uwot wrote: Wed Feb 22, 2017 9:51 pm I think observation is the starting point for physics; if the logical conclusions don't conform with observation, then either the logic is wrong, or the universe isn't logical.
There is no reason to expect the universe to conform to human logic, however it is reasonable to expect human logic to conform to the universe or what is observed.
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Re: How does gravity work?

Post by uwot »

thedoc wrote: Sun Aug 27, 2017 11:44 pm
uwot wrote: Wed Feb 22, 2017 9:51 pm I think observation is the starting point for physics; if the logical conclusions don't conform with observation, then either the logic is wrong, or the universe isn't logical.
There is no reason to expect the universe to conform to human logic...
Well logic is a set of rules for language, and you are quite right, there is no reason to expect nature to behave in the same way as words.
thedoc wrote: Sun Aug 27, 2017 11:44 pm...however it is reasonable to expect human logic to conform to the universe or what is observed.
I'll defer to any logicians on this one, it's not my field, but as I understand it, there are various types of fuzzy logic, that attempt to take account of the observed behaviour, particularly of quantum particles. So yes, given that some logic is predicated on actual events, it would be surprising if it didn't conform to those events.
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