gravity 101

[yusufcam]

(just trying to get a mental image of how gravity works, thanks in advance :))

if gravity is the weak force in nature and is believed to occur through the curvature of space/time. How does the sun which is comparable in scale to a soccer ball hold the earth (the size of a marble) in gravitational orbit at 200 mtrs?

either the scales are wrong, or the indentation type graphic images they use to communicate space/time curvature is misleading.

[xelasnave]

Hi Colin
I am not a scientist but I am interested in gravity.
I don't understand your concern about gravity being a weak force and the Earth and Sun.
I have not yet found the answer as to how gravity works.
Also I think that GR does not say gravity is seen as a force.

[yusufcam]

hi,

put slightly differently, the way gravity is portrayed as far as i can tell is an effect like displacement like an object in water, but curvature in space/time.

whereas there is no such similar displacement ratios, between the relative size of the sun and earth (let alone the far outer planets), which comes close to the effect that gravity has, to cause planets to orbit which is displacement orientated.

does that make sense?

Is space/time an object, if not how can an object effect it?

just trying to understand how it works, or what might be wrong with that line of understanding above, which would make it clear how it is proposed to work.

not a problem, just curious.

thanks

[xelasnave]

Colin
I spent 5 years formulating a gravity hypothesis that speculated gravity was a sort of pressure system, which could be called push gravity, in an effort to describe how gravity worked.
Having worked it out I found that the idea was not new but was first put forward in 1745 by a man named Let Sage.
That approach fell out of favour at the turn of the century but I must say I like it still.
The idea needs an eather which SR and GR does not need.
I seek an answer that required some sort of particle interaction and I don't think that is available.
GR works very well but I can not imagine the reality it describes.

[julianh72]

If you could arrange for a soccer ball and a marble to be 200 metres apart in space, and contrive to have them with appropriate initial velocities with respect to each other, the marble would indeed orbit the soccer ball.

Let's assume the soccer ball has a mass of 1 kg, and the marble has a mass of 10 grams. For a circular orbit with a radius of 200 metres, the attractive force is 1.7 x 10^(-17) newtons, and the marble needs a tangential velocity of about 0.6 microns per second, and would have an orbital period of 69 years! (At a radius of just 1 metre, the orbital period would be "only" 9 days.)

[yusufcam]

hi julian,

hmm, interesting.

so what is gravity?

[yusufcam]

okay, so an image just came to mind. Gravity isn't a displacement force but the image in space/time of a contractual force. Thus a neutron star which is significantly more weighter (contracted) but smaller than the sun has significantly more gravity.

(hmm, just noticed a potential problem with that idea, and that is that the image would be retained where the contraction took place rather than follow the object around. Unless space/time is of a different quality to physical objects. Like the point of time of the contraction follows the object. who knows).

yes/no?

[julianh72]

"Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity, not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass/energy."
http://en.wikipedia.org/wiki/Gravity

If you're asking "Why is there gravity?" or "How does gravity work?" - well, if I could answer that, I'd probably have a Nobel Prize!

[michaellxv]

I think part of the problem in visualising this is that the soccer ball vs marble scale is wrong in every way.

With reference to sun fact sheet (http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html) and solar system scale (http://thinkzone.wlonk.com/SS/SolarSystemModel.php?obj=Sun&dia=1m&table=y&map=n) a 1m diameter sun would require a 9mm (small marble) earth with orbital radius 107.5m . The scaled masses are 734kg sun 2.2g earth.

Most graphical representations just don't show this relative scale, particularly with the mass which is very relevant when talking about gravity.

Michael.

[yusufcam]

hi michael,

yes, the exact scales i could not recall, but your right its about mass, as the issue is about, i am guessing a contracting force rather displacing force in space/time.

but its interesting.

[yusufcam]

i suppose i am just wondering if there is a simple laymens way to understand these topics.

the idea that gravity is a contraction of space/time would appear to work with the idea that time slows down under increased gravitational effects.

its just brainstorming, and interesting for me.

[michaellxv]

I don't see it as a contraction of space. If you place 2 equal mass objects in space with no motion (and no other external forces) then when released they will move through the space between them until they collide.

On the other hand gravity seems to be able to resist the expansion of space. The universe is expanding, distant galaxies are receding due to the expansion of space. But locally, in our solar system/galaxy/local group, we don't see this effect, gravity is holding it all together. Now that makes my brain hurt.

[bojan]

It is a curvature or distortion of space-time, caused by th epresence of mass.
More reading about the issue is here:
https://en.wikipedia.org/wiki/Gravity

[xelasnave]

And energy...as well as mass I believe

The question is for me is what cause the curvature...
How does mass (or energy) tell space time how to curve.
How can GR and quantum be united.
Surely space time must have a physical expression via some sort of particle to communicate
At some level there must be a physical system to communicate between mass space time and energy.

[bojan]

Correct.. mass = energy.

Particle (still hypothetical, of course) is Graviton :-)

[xelasnave]

The graviton seems difficult to observe.
The only hope is detecting waves of them which is still difficult..still looking for them

[Eratosthenes]

It's the field that is key in many of the theories that Physicists describe. The particle is a manifestation or perturbation in the field. So for example the Higgs Boson is a tiny vibration in the Higgs field (analogous to the Photon being a tiny vibration in the Electromagnetic field). Detecting a particle like the Higgs Boson (or its decay products) is evidence for the existence of a Higgs Field. The Higgs boson is difficult to detect because its difficult to produce in the laboratory. The Higgs boson is a heavy particle which doesn't interact too much with other field. You need to generate an enormous amount of energy in a tiny space to produce Higgs Bosons - hence the construction of the massive 10 billion dollar Large Hadron Collider.

The detection of the Graviton is an interesting one because it's a hypothetical particle which, like the photon, has no mass. (like the Higgs particle, the Graviton is also a boson).

If the Higgs field (particle) is responsible for the property of "mass" in the Universe, can we assume that the Higgs particle is some how intertwined with the Graviton?? (both are supposedly classified as bosons. Although the Higgs field doesnt interact with other fields? Not like the TOP quark, which is a heavier particle than the Higgs Boson but can interact and therefore a little easier to produce and detect):shrug:

[xelasnave]

Thank you Peter
Let's try and describe the situation using a ball and a marble.
Is there a field between them which is a flow of gravitons travelling at or near C.
Do you know how information is transferee in a field.

[Eratosthenes]

what do you mean by information?

"information" can have a different meaning in different contexts or situation (such as in statistics, or quantum physics)

I remember the debate involving "spooky action at a distance" or entanglement where two coupled particles are separated at the extremes of the universe and an observation is made on one of the particles. For example its spin is detected - then the spin of the other particle will be determined instantaneously. Was the speed of light limit broken for this instantaneous transfer of "information" to occur?

[xelasnave]

I was more interested in how you would describe the relationship between a marble and a ball, similar to the op, using hypothetical gravitons . How do they act with the ball and the marble. I ask as much for speculation but upon the model gravitons would allow.

[Eratosthenes]

I tend to think in terms of fields with particles being tiny local vibrations in the field.

what if you had two magnetic objects? Are there "magnetons" between the two objects imparting information and dictating how the objects behave??

(perhaps Entropy should be dragged into this "information" concept that you raise?)

[sjastro]

(1) The Higgs field is responsible for mass not the Higgs boson.
(2) The Higgs particle is only "associated" with bosons having mass such as the W and Z bosons through spontaneous symmetry breaking of the electroweak force. Gravitons are massless.
(3) The Higgs field is only accountable for about one percent of the observable mass in the Universe. While the Higgs field accounts for all the quark mass, it only accounts for about one percent of the mass of protons and neutrons each of which are composed of three quarks. The reason for this discrepancy is that 99% of the proton and neutron mass is taken up by binding energy that holds the quarks together which is not attributed to the Higgs field.
(4) Given the Top quark was the sixth and last quark to be discovered it was certainly not easier to produce and detect.
The larger mass required more powerful particle accelerators to produce the Top quark. Then there was the added complication that the Top quark immediately decayed into a Bottom quark which in turn decayed into a Charm quark which in turn decayed into a Strange quark. The difficult was digging out the signal attributed to the Top quark and not to the decay products.

[xelasnave]

Thanks for trying to answer my question Peter.
Unfortunately I am still in the dark.
Irrespective of how the H graviton is describes how does it work between the ball and the marble.

[Eratosthenes]

I wouldnt even attempt to answer you question - just posed some questions. I am always in the dark:D

Of course one can just read accepted current doctrine from the text books and parrot them, or cite some peer reviewed articles to paint a nice safe portrait, but I feel the interesting stuff resides in the unanswered questions and philosophical speculations. Never fear the paid paranoid priests who guard the Temples and worship the plastic scriptures;)

[sjastro]

Alex,

Let's have a look at your marble/ball example and why gravitons fail miserably to explain the gravitational interaction between the two.
In this case the marble and ball are treated as point masses.

Since gravitons involve a quantum field theory of gravity one needs to look at the initial and final quantum states.
In this case the initial quantum state could simply be the marble and ball before interaction, the final quantum state is the gravitational interaction between the two.
In between the initial and final states are the intermediate quantum states involving the creation of the graviton and it's momentum, plus the momentum of the marble and ball etc.
The exercise is to sum over the various momenta in each state that produces an answer that not only makes sense but agrees with experiment and observation.
Let's keep this idea to the side for the time being.

In the same way we can examine the electromagnetic interaction between two charged particles involving the creation of virtual photons.
Recall in a PM I introduced you to the concept of Compton wavelength as a way to explain the BB singularity.
When two charged particles interact and a photon is emitted, the particles undergo a resonance which smears the particles over space time.
The particles are no longer considered point sizes of zero dimension but are at dimensions comparable to their Compton wavelength.
This is important has it allows energy limits to be imposed much like the case of String Theory using renormalization. By utilizing renormalization and summing over the momenta for all the initial, intermediate and final states a finite value is obtained.

Unfortunately when it comes to a Quantum field of gravity there is no way we can treat a particle as anything but a point source. Since a point source has a zero radius we find by summing over the momenta we obtain infinite values.
If the particle is treated as a string or a loop which has an infinitesimally small but non zero dimension we have what is known as a renormalizable theory.

Unfortunately a quantum field theory for gravity is non renormalizable.
Until physicists can produce a renormalizable theory one can argue that gravitons don't even exist from a theoretical viewpoint unless one assumes that String or Loop quantum gravity theory is correct which also predicts gravitons.

Steven

[xelasnave]

Hi Peter
I just thought you may have had a speculative view on the matter.

[xelasnave]

Thanks Steven.
So all we need is a new formula
Can you come up with what they need.
You should at least write a book.

[bojan]

I think this is unfair statement.
Until we know all the facts, including the way of thinkng of mainstream "priests", the wild speculatios can make you feel good.. but they will not place you any closer to the reality.

What Alex was always after (we had quite a lot of good discussions in the past on this forum) is simple explanation, mechanic of the gravitation phenomenon.
This way of thinking is natural for all of us humans.. because majority of us want to relate to our everyday experience.

Sometimes this is not possible, simply because our brains are not wired to understand QED (myself included. Feynman said the same to himself.. for completely other reasons I think... )... they are basically wired to keep us fed and away from danger of being eaten by predators.
It is a wonderful and quite accidental byproduct of our brains functionality evolution that we humans are capable of abstract concepts at all (math).. and also sometimes capable of finding appropriate analogies to help the less skilled in abstract thinking to better understand those concepts..
And don't forget, those less capable thinkers are acually majority, so they are those taxpayers who are paying the bills for majority of that small minority of abstract thinkers ;)

[xelasnave]

Read up on renormalisation.
I gave up on push gravity as it seemed to me one could only end up with infinite situations when trying to record all the interaction.
Did I get right.
I think I can understand

[Eratosthenes]

...its more of a cynical statement bojan. Scientific research today (and for some time) tends to be conservative, boring and lacking in imagination and risk taking. Some areas of research are still vibrant and plowing along but generally the science that is conducted today just doesnt compare with the epochs that spewed out quantum mechanics or general relativity.

I suspect that the current Corpocracy has spread its tentacles to the sphere of science and engineering. In a sense science has been contaminated by corporations and their short term profit making ideology. Where are the dreamers today? What are we doing in the area of Space exploration apart from probes and some space telescopes? In the late 1960s when humans landed on the moon, the feeling in the general population as well as among scientists was that by the year 2000 a lunar base would have been set up and planetary landings planned soon after.

Just to give you an example. In the cancer research area, very little funding is directed towards cancers that dont effect huge numbers of people. Its a business model mentality. Can the Pharmaceutical companies get their money back and how fast?

Almost half the scientists and engineers in the US are directly or indirectly linked to the military industrial complex. In fact the top graduates are head hunted by the military industrial complex and stock market analysts.

Why sweat away in a University trying to carry out fundamental research or pushing the boundaries of knowledge and technology, when you can earn ten times the money working in the stock market developing day trading algorithms or designing cluster bombs for Raytheon?

Look at the Nobel Prizes handed out these days. They generally dont have have the depth and importance when compared to the first 60 years of Nobel prizes. How does one rate a Nobel prize for the invention of a blue LED about a decade ago with Dirac's or Shoredinger's Nobel Prize? Even the Nobel Peace prices have been trivialised and politicised.

Cynicism is generally counter productive, but I think science today deserves all it gets - generally boring riskless profit making ventures. Pathetic really - when science is one of the most magnificent tools of discover uncovered by humans. (and we can thanks Eratosthenes in about 190 BC for kicking off the scientific method in earnest)

[bojan]

Actually, I couldn't agree more with what you wrote here... A movie "Idiocracy" comes to mind..
But.. all this is a hard reality, unfortunalely - we all have to eat - and the only way to improve this situation is education of people... which is extremely important and sensitive activity (it must be conducted in a right way, with almost individual approach.. because what works for me won't work for Alex and vice versa), and at the same time it is very non-profitable, money-throwing exercise from fiscal and business point of view.

Back to analogies..

When thinking about counter-intuitive concepts of residual and/or "emerging" forces, aerodinamic lift comes to my mind.
I bet that 90% of public do not realise that the force that keeps the aircraft in the air is a result of difference of speeds of airflow below and above the wing.. resulting in difference of static pressures between upper and lower side.. and hence the lift.

This is another interesting read on gravity as emerging force:
http://en.wikipedia.org/wiki/Entropic_gravity
http://arstechnica.com/science/2011/04/is-gravity-a-result-of-thermodynamics/

[yusufcam]

makes sense, in the sense of how you get from the clumping of moleculular particles of dust into a star, then from there to a curvature of space/time.

but that would describe the effect rather than the cause, yes/no?

(its possible the cause is in there, just couldn't weed it out in laymens terms, wasn't it feynman who (also :)) said if you can't explain something simply you haven't understood it.)

[bojan]

It seems so..
well, all theories are only more or less accurate descriptions of reality, IMO.

[yusufcam]

you mean like words can only be symbols (abstractions to a degree)? suppose thats why science likes maths.

but they both point to comprehension, so there's a way to go yet, for me at least in getting a mental grasp of what gravity might be.

[bojan]

Exactly so.
Math is the only language that can consistently describe the reality.
Words are not good enough because in most cases they do not have defined meaninings and defined relationships between themselves ("What poet meant to say with those words" were my favourite expression to describe this situation).

[sjastro]

Since Maths has come up in the discussion it can be used to answer your original question whether space time curvature diagrams of say the solar system is an accurate representation.

Space time curvature flattens out as one moves away from the Sun.
The amount of curvature is of the order 2MG/(r*c)^2.
M is the mass of the Sun, G is the gravitational constant, r is the distance from the Sun, c is the speed of light.

Using Mercury as an example where space time curvature does cause its orbit to vary from the classical Keplerian orbit, the calculated curvature is approximately 0.0000000000000000001.:eyepop:
Even at the surface of the Sun the curvature is around 0.0000000000000009.

Given that totally flat space has a curvature of zero, the measurable effects of space time curvature is extremely small at least when applied to the solar system.
Hence the representation is grossly exaggerated.

The situation is very different however as one gets close to extremely dense objects such as black holes.

Steven

[yusufcam]

thank you,

i suppose to more accurately reflect the original question, would be to ask how an object curves space time.

i would guess that its isn't by displacement in a body (space time) but through the force that contracted the body pulling spacetime in towards it with it. like a weighted object dropped on a sheet and pulling in the sheet around it, except its not dropped but contracted into itself.

now to say that gravity is the curvature of space time is good for working out how orbits work, but i am not so sure this model would explain how gas clouds collapse/gravitate into stars. Then i suspect you are looking at gravity as an active force.

the emergent idea may make sense here, that gravity works differently at different levels.

a simple view, but i am wondering if it can be explained at these levels.

[sjastro]

No one knows how a mass curves space time because General Relativity is only a semi phenomenological theory where the emphasis is to explain the effect rather than the cause. It explains the concept of the Newtonian potential of gravity as a distortion of space time without explaining how space time curves. Newtonian gravity is purely a phenomenological theory as it offers absolutely no reason for the cause behind gravity.

The use of General Relativity for working out orbits has only a very limited application.
Firstly there needs to an enormous difference in mass between the central body and the orbiting body. Mathematically the orbiting body is known as a test mass, a mass which is not large enough not to create its own space time curvature.
Secondly the orbiting body needs to be sufficiently close to the central mass and/or the mass/density of the central body is great enough for space time curvature to be significant.

With the exception of Mercury all other planets are described by Newtonian physics where planets orbit in 3 dimensional flat space and gravity is a force.
Similarly the formation of stars is also based on the Newtonian version of gravity.

While it appears that Newtonian physics and General Relativity are two totally different theories of gravity there is a subtle connection between the two. Newtonian gravity is a first order approximation to General Relativity.
If you took the mathematics behind General Relativity and applied "normal conditions" (low gravity conditions and velocities well below the speed of light) the equations break down to Newton's equations.

Steven

[Dave2042]

Excellent explanation.

That said, it's possible to go further than this. The idea that space-time is 'really' 'curved' only arises because we look at the maths of GR and insist on interpreting it in a way that makes intuitive sense to us in the context of the low energy conditions we usually experience.

Personally I find that a very useful way of thinking about it, however it's worth remembering that the physical theory is just a bunch of equations expressing relationships between directly observable quantities, and the actual curvature of space-time is only indirectly observed.

Occasionally it becomes very important to remember that the interpretation attaching to the indirect things is not necessarily real, just useful. A good example of this is the idea of the electromagnetic field. Very important in classical EM, but starts to look distinctly less real in the Feynmann approach (glossing over a lot of technical stuff).

[yusufcam]

thanks, thats quite informative...

it does open a different door though, is space/time considered a void or an object.

if its a vaccuum how does an object effect it?

its curious stuff.

[sjastro]

Very true.
The electromagnetic interaction between a positron and electron via a Feynmann diagram is most intriguing as it suggests that a positron is nothing more than an electron travelling backwards in time.

Steven

[sjastro]

If an object is defined by possessing certain properties than space-time is most definitely an "object".
The geometry of space-time is a property that can be determined by a fundamental property of light. Light will always travel along the shortest pathway. If space-time is flat, light will travel in a straight line, if the geometry of space-time is curved like on the surface of a ball, light will travel along an arc.

We can observe the bending of light as it travels through pockets of space time that are not flat, such as gravitational arcs observed in galaxy clusters or the position of stars near the limb of a solar eclipse that are slightly displaced when compared to their positions in the night sky.

Vacuum has a somewhat different connotation. The electric field around a charged particle possesses quantum properties like the particle. The energy levels of a field can be quantized like the energy levels of electrons in an atom.
A vacuum in this case is a field with the lowest energy level.

There a different types of vacuums as well. Apart from an electromagnetic vacuum there is also vacuum relating to the strong nuclear force.

Steven

[Eratosthenes]

good example bojan,

The Bernoulli effect is counter intuitive. If you hang two ping pong balls from the ceiling with pieces of string, separated by a small gap and then blow air into the gap between the ping pong balls, one's intuition says that the balls should fly apart - ie the air should push the balls apart. And yet the Bernoulli effect causes the balls to comes close together and even touch.

[yusufcam]

well, its great feedback for my question, and thanks. now to digest it :thumbsup:.

[Eratosthenes]

which matter is that exactly Alex - I don't quite follow you?:question:

(remember Alex, pure mathematical notions are abstract constructs - even mathematical axioms which everything in the field henceforth relies upon. Many mathematical philosophers are adamant that absolute reality and truth (whatever these concepts are) can only be described by mathematical laws and their proofs. Would that imply that reality/truth is abstract by definition? I have a friend who is a research mathematician in academia, who has often argued with me over this very point - he stance is basically "truth can only be mathematically described". I have always wondered why there is no mathematical category in the Nobel Prize medals. They have the Fields medal to give out every 4 years. That Pythagoras has a lot to answer for with his first proof)

[xelasnave]

Peter don't worry about my question I have my answer.

[g__day]

Gravity is the topology of 4D space-time caused by the distrbution of energy and mass within it!

[Eratosthenes]

....in other words gravity emerges from the lowest vibration of a closed string

[bojan]

Links to a documents that discuss this aspect:
http://arxiv.org/pdf/1001.0785v1.pdf
http://www.researchgate.net/profile/Erik_Verlinde2/publication/45893653_On_the_Origin_of_Gravity_a nd_the_Laws_of_Newton/links/02e7e525c95a0f0d4b000000.pdf

[Eratosthenes]

good sources bojan....

.....what is your View on Sheldon Gao's counter arguments that try to refute Verlinde's notion that Gravity is an entropic force?

[bojan]

Still reading and trying to digest the first paper :D
So, no comment... yet



BTW.. there are also counterarguments on counterarguments available.... watch this space :P
http://www.researchgate.net/publication/45904402_Comments_on_and_Comments_o n_Comments_on_Verlinde%27s_paper_On _the_Origin_of_Gravity_and_the_Laws _of_Newton

[sjastro]

Wrong conclusion to Matthew's post.
When does a string exist in (3+1) space-time?

[sjastro]

Hmmm.

One argument against entropic gravity is the humble double slit experiment.
If you shot neutrons at the slits the quantum wavefunction of the neutron before the measurement is made is a linear combination of the Quantum states Ia> + Ib>.
Here Ia> could mean the neutron passes through the left hand slit and Ib> the neutron passes through the right hand slit.

If you rotate the slits 90 degrees so one slit is on top of the other, the slits exist in two different gravitational potentials.
Now according to entropic gravity if the holographic screen is at some distance below the bottom slit, the number of possible microstates which is a measurement of entropy increases as one gets further away from the screen.
Hence the top slit has many more microstates than the bottom slit even if the slits are separated by only the Compton wavelength of the neutron.

The problem is these microstates need to be considered in the quantum wavefunction. The quantum wavefunction is no longer simply Ia> + Ib>.

The difference in the number of microstates between the top and bottom slits would destroy the observed interference pattern as observed in the slit experiment as the probabilities of where the neutron hits the detector behind the slits have been changed.

Steven

[bojan]

Interesting..
But... In the real experiment, aren't the diffraction patters for both cases the same? or different and by how much?
I presume you used neutron example because of it's rest mass and because it is not influenced by electrical fields?

[sjastro]

Experiments show the orientation of the slits doesn't effect the observed interference pattern.
Before the observation is made the neutron is in a superimposed quantum state Ia>+Ib>.
Mathematically each state Ia> and Ib> has the same dimension or contains the same number of terms for superimposition to occur.
In the case of entropic gravity the neutron passing through the higher slit has many more terms describing it's quantum state when compared to when it passes through the lower slit.
Mathematically it is not possible to form a superimposed quantum state.

The lack of a superimposed state means that quantum interference cannot occur and one would not expect to see an interference pattern if the model of entropic gravity is correct.

One can use protons, electrons, even buckyballs instead of neutrons.

Steven

[xelasnave]

Now you have let the cat out of the box Steven.
I have spent some time trying to understand this via a google and I miss the significance of why the difference in states matters..I am frustrated that I can't understand.
Nevertheless thank for making me aware of it..sorry I no longer have the mental power to digest even what quantum physics is trying to say.
I bet you are a good poker player or would be.

[Eratosthenes]

"I think I can safely say that nobody understands Quantum Mechanics"
"Anyone who claims to understand Quantum Theory is either lying or crazy"

(Richard Feynman)

[xelasnave]

But he was only a drummer.

[Eratosthenes]

...mainly bongos

[sjastro]

Alex,

Quantum states are described using Dirac's Bra-Ket notation (https://en.wikipedia.org/wiki/Bra%E2%80%93ket_notation).

The Quantum states are mathematically handled as single column or row matrices.
A superimposed quantum state such as a neutron before it hits the detector in the double slit experiment is in the form Ia>+ Ib>.
This involves matrix addition.
For matrix addition to occur the wavefunctions Ia> and Ib> must contain the same number of matrix elements.

However as has been pointed out if entropic gravity is correct the upper slit has many more microstates than the lower slit in which case Ia> and Ib> now longer contain the same number of elements.
Matrix addition is impossible and a superimposed quantum state cannot be formed.
The familiar interference pattern observed on the detector screen caused by the collapse of the superimposed quantum state should not be observed simply because there is no superimposed state to start with.

This a mathematical argument against entropic gravity.
The issue is on the validity of whether the thermodynamic microstates themselves can form the basis of the wavefunctions.
Another argument purely from a physics perspective is the different gravitational "environments" of the lower and upper slits results in quantum decoherence which would destroy the observed interference pattern.

Steven

[xelasnave]

Thanks Steven
As always you help gell what I have been reading.
Yesterday I spent too much time reading when I was not comprehending, but something remains.
I do think quantifying nothing is impossible because from my humble view re numbers even if taken from the simplest experiment are really infinite and the only way you could manage the numbers was by probability related to time and well a multitude of things...but I wondered does our rounding off the numbers to manager amounts hide something.
My point is can we really ever describe the quantum reality with maths.
I am really going to think about this.
Up side..although I don't do the math I am starting to understand a few things and how maths works.
This must do me good, I mean at my age 68 reading what I find demanding must help the old grey matter.

[sjastro]

The mathematics allows us to define the probability of a particle existing in a particular state which is basically what Quantum Mechanics is about.
While Quantum Mechanics is counter-intuitive, the "reality" of the theory can be gauged by the technological advances made.

As Steven Weinberg the Nobel Prize Winner for his work in Electroweak theory once stated, if Quantum Mechanics suddenly "stopped working" our technology would be driven back into the late 19th century.

Steven

[xelasnave]

How many cats did or did not suffer at the hands of quantum mechanics

[Eratosthenes]

Generally Classical mechanics is way more complicated mathematically than Quantum Mechanics. The issue with Quantum mechanics is its counter intuitive physical implications.

Also many people think Quantum Mechanical effects only apply to the microscopic or atomic world - this is a miss reading of the theory. QM effects apply at all scales, but at large scales these effects are not noticeable and "drowned out" by other effects such as Gravity etc.

It will be interesting to see if human creativity and genius can discover a deterministic theory of the atomic domain. As it stands the experimental evidence in support of Quantum Physics is vast and as yet contains no counter evidence (tmk).

The field of Physics is very fortunate in that it deals with the simplest aspects of reality. Physics is by far the most idealistic and simplistic of scientific endeavors. Physicist often tend to hide behind mathematical axioms and dogmatic rhetoric which isn't necessarily a negative thing - but it does result in a very simplistic and easy scientific discipline. The jump in complexity from Physics to Chemistry is huge - and an equally huge jump occurs when one moves into Biology (and forget about trying to understand Psychology or economics - these are the realms where educated guess work becomes equally important as theory)

[xelasnave]

I find the simplest thing complex.
We talk about a photon giving it a simple description but how complex may it be. We treat it as an elementary particle but I wonder what are it's parts. We treat it like a
Like a simple cell..simple at one level..a single cell small etc....but when we really look at a cell we find a complexity that engaged some scientists for their lifes work.

[xelasnave]

I think even if one knows everything humans know it is a small fraction of what is reality..whatever that is.
Back to the cave for me.

[Eratosthenes]

Alex,

Einstein thought that equations and relationships that were messy, complex and ugly looking were probably wrong - he preferred simplicity and beauty in natural forms and processes (probably explains his long opposition to the fundamentals of QM - not sure if he changed his stance by the time he retired).

(I recall a German Physicist named Peter Bergmann who visited our University in the early 1990s. He gave several public lectures on the various Unified Field Theories that were floating around at the time. Many of the questions that were fired at him after his talks related to his relationship with Einstein. He told the audience that Einstein never stopped working on these ideas - it must be a tough nut to crack :D )

[xelasnave]

Yes but he was just a clerk.

[Eratosthenes]

...his parents also thought that there was something wrong with him because he didnt speak until the age of 4

[bojan]

Alex,
The problem is the way our brain works.
Our firmware (layer one) is tuned/adapted for own survival as individuals and as species.. The second layer is tuned for interaction among ourselves in a groups (family, pack, nations).

So.. we simply do not have intuitive tool to "understand" the behavior of individual electron, photon.. because they are too tiny for the scale of things we live in and therefore outside our world, so to speak.
What we can percieve though is the group behavior of huge number of those indivudal particles, this is what we can "understand' and see as rock, air, water.. other people..


You can find the same (quite broadened actually) answer, put in other words in Peter's reply (and very illustrative, and actually spot-on):


Photon is not a complex thing at all. It does certain things, under certain conditions.
This behaviour can be precisely described by math.
And that is all there is.

[xelasnave]

My point is ...math is unavailable in my reasoning.
I think however I can visualise very well.
When I visualise what I create is complex.
Once the atom was considered differently and viewed as a single unit but as time saw more research the atom is found to have many parts.
I always think this way such that even when I wonder about a photon say my imagination presents pictures of what it may look like etc.
When I imagine nothing, space, I see something very complex, such that I have trouble fitting all I imagine is found in an empty part of space.
Anyways that's not at all important and I am sorry that I comment upon it.
And I understand and accept how useful and important math is in helping us quantify reality. I think there is more than we can describe.

Thanks for the wonderful input.

[bojan]

The attempt itself to visualise is actually a huge problem..
Because, in order to see clearly the electron inside atom, you have to shine a ligh on it, right? And that light must be of a short wavelength.. to be able to see clearly wher ethe electron is..
And our "visualization" firmware in our brains totaly relies on the assumption (almost fact!) that the light reflects from object without changing the object itself.... which can't be further from the truth.
The moment the light is supposedly "reflected" from the electron (which never happens in reality, thi is experimental fact), it is not there any more. So what you see is NOT what you get;)

[sjastro]

You obviously know very little about the mathematics of either subject.
At what level of Quantum Mechanics does your comparison with Classical Mechanics end?
If you include relativistic Quantum mechanics or Quantum Field Theory in the picture there is absolutely no doubt the mathematics is vastly more complicated than Classical Mechanics.

Given the mathematics of Classical Mechanics is contained within Quantum Mechanics through Hamiltonian physics (advanced Classical Mechanics) the comparison is pointless anyway.



Physicists use mathematical models, mathematicians use mathematics.
You fail to see the distinction. Mathematical models by their very nature are far less rigorous.
Einstein summarized it perfectly when he stated the left hand side of his field equations were made out of stone but the right hand side out of straw.
The left hand side is based on Riemannian geometry, the right hand side on brilliant physical insights that could not be derived through axiomatic mathematics.

The idea that physics is "simple" because the mathematical axioms automatically take care of it is so patently wrong as is demonstrated by Ed Witten.
Witten is the only physicist to have won the Fields Medal in Mathematics has found many concepts in Quantum Field Theory which were originally developed as ad hoc ideas can be proven mathematically.
In this case the physics preceded the mathematics not the other way around.

If physics "deals with the simplest aspects of reality" then why is Quantum Mechanics counterintuitive?
A contradiction in terms.

[bojan]

Steven,
IMO "intuitivness" is related to the higher functionality of our brains.. which evolved in a world we live in (in other words, the scale larger than atom, smaller than universe).

"Simplicity" (IMO again of course) actually means the lower position of processes on the hierachical ladder of human affairs.. ( it goes like this: QEM, classical phisics, chemistry, phychology, economics, politics).
So I don't think the statement that QEM is counterintuitve is actually a contradiction in terms.. it just reflects the way human animal thinks.

[julianh72]

Maybe his parents just hadn't said anything interesting to him until then!

[Eratosthenes]

Only if you interfere with it as an observer (ie collapse the wave function). Until then you know very little about a single photon. You dont even know if it's a particle or wave or both or neither. This is the beauty of Quantum Mechanics - its an extreme form of philosophical cowardice

What does the mathematics say about a photon entering a black hole/singularity?

[Eratosthenes]

You raise a very important point Alex.

Amongst mathematicians/Philosophers etc, there is even disagreement as to whether numbers themselves exist - numeracy being one of the more simpler forms in the field of mathematics. Generally there are 3 broad groups where mathematicians and philosophers fall into on the issue of whether numbers are real and exist in the sense that a cricket bat or coin exists.

Platonism, Nominalism and Fictionalism. Platonists view numbers as abstract entities that basically exist outside time and space - the numbers don't interact with reality like a car would for example. So the Platonic stance is that numbers exist but they are more interested in their context and location and that location is not in our reality.
Nominalists are a little bit more practical in that they view and use numbers to describe things in our reality - they kind of attach or couple numerical values to real objects. They are sort of practical Platonists in that they arent concerned pedantically about whether numbers are abstract or exist outside our reality. Fictionalists dismiss numbers as real and prefer to think of numbers as not existing anywhere at all. They also claim that mathematics itself is inherently FALSE. The way fictionalists deal with the success of mathematics/science in our practical world, is that they merely contend that success or efficiency is NOT a reflection of truth.

The Platonists do have an advantage when dealing with imaginary numbers (i), zero, infinity and transcendental numbers (like pi and e) - they merely treat them as abstract objects that exist outside out normal space-time regime (no different to the number 57 or the fraction 1/3).

There are many mathematicians, scientists and even philosophers who really aren't concerned about these issues - if it works and pays the bills and keeps the board of directors happy, then that's all that matters. Sort like Corporatised puppets dangling in the profit winds of the pseudo free market regime. Sadly, most of today's scientists, mathematicians and in particular physicists are disappointing corpocratic puppets who are dishonoring the great feats of the giants who came before them.

It's really sad to see the great discipline of Physics in particular collapse into a pathetic dogmatic cult religion.:D

[xelasnave]

Thank you Peter for taking the time to construct your post.
I am not sure in which box I should go in...other than t
he one in which I shall be buried.

It occurred to me maybe my early career in law makes me think differently.
One is often looking for "what else" and always trying to get around an established law or custom which stands in the way of victory.

In any event I am happy with my abilities for my age and grateful so many wonderful people indulge my ignorance and help me understand the world of science , it's results andsystems.
.

[Eratosthenes]

interesting Alex that you hovered amongst lawyers.

I have always considered lawyers close to the most important profession in society along with medicine and education. And it's for this reason that I suspect that the profession of Law is the most corrupted. The consequences of a legal system that is applied equally amongst its citizens is just way too threatening for the Oligarchical power structures to endure IMO.

I recall story about a defendant, after being sentenced severely by a judge screaming out the words "You call this a court of Justice" - and the judge replied, this is not a court of Justice, it is a court of Law.

I wonder at what point in history did Justice and the Law diverged into unrecognisable phenomena?

Yes ladies and gentlemen, the Law protects YOU KNOW WHO, and for YOU KNOW WHAT.

...back to the issue of gravity - some describe gravity as an illusion

[xelasnave]

Peter could you expand upon and explain your last sentence.

[Eratosthenes]

http://www.sns.ias.edu/~malda/sciam-maldacena-3a.pdf

https://m.youtube.com/watch?v=NblR01hHK6U

There are some interesting articles on the illusion of gravity - in fact Einstein referred to the illusion of gravity many times

[xelasnave]

Thank you Peter.
Newton said gravity was the force of God or words implying similar.
GR needs no force.
Equivalences suggests fictitious force.
Is there a reason the concept of force seems to be avoided.

[sjastro]

Einstein referred to gravity as a fictitious force. Fictitious forces are not illusionary because they can be measured.
An accelerometer located inside a car will measure the backwards proper acceleration (https://en.wikipedia.org/wiki/Proper_acceleration) due to the fictitious force as the car is subjected to a forward coordinate acceleration (https://en.wikipedia.org/wiki/Acceleration).
When you stand on your bathroom scales the proper acceleration is directed upwards and opposite to the coordinate acceleration due to gravity.
Otherwise you would fall straight through the scales.

[Eratosthenes]

.... on that reasoning, all forces may well be fictitious in essence, or perhaps merely different manifestations of the same entity/phenomena??

sadly scientific disciplines such as physics have been corporatised on an almost global scale with only small pockets of cutting edge research. In the USA for example the elite Physics and mathematics PhDs end up being snapped up by the Pentagon (working on WMDs, defense systems etc) and the Stock market (working on market predictions and other complex systems). They sometimes receive an order of magnitude additional pay to carry out these ridiculous projects motivated by paranoia, fascist ideologies and material greed.

Mediocre physicists such as Lawrence Krause, Green and De Grasse are left to gallop around the planet promoting Atheism and pedaling trivial sensationalist Physics - the cartoon characters of Academic Hollywood.

Science has essentially become a corporate cult religion - and driving itself backwards in a real hurry - if it wasnt globally pathetic it would be a gut splitting stage comedy. :D

[xelasnave]

Steven I read the links you posted and I found them very helpful. Thank you.
Peter I am just a layman and so cannot comment on your view of the world of science other than to say it is an ill wind that does not blow some good.
I see it this way..it is good that there is paid work for folk who have taken time to gain respectable qualifications, even if it is the Pentagon.
The military gives us many inventions that finally benefit the public.
I think glad wrap was originally a worked up version of protective covering for jets on aircraft carriers.
As for preaching atheism I applaude such.
I believe religion has past it's use by date.
Any attempt to bring humans out of the dark ages must be good.

I still don't understand the choice of words "fictitious force.
In law there was a time where "fictions" were used...perhaps my response is due to having to study why their use was necessary.

[Eratosthenes]

Atheism is just another fundamentalist religion sprinkled with its fair share of dogmatism and fanaticism.

A little bit like Science actually:D

[RB]

Topic is Gravity guys.

:)

[xelasnave]

Side issues really and irrelevant to gravity.
I once believed there could be no force of attraction...how say you.

[xelasnave]

In reflection I withdraw my question.

[Eratosthenes]

....the force of attraction between two oppositely charged particles is only partially true and dependent on the separation distance. Opposite charges will attract one another, but when the distance becomes very small, there is a repulsive force.

It's often said that in personal relationships, opposites attract. Well it could mean that this is true only up to a point - close relationships between opposite characters are repelled - opposites keeping their distance. What is that repulsive force again?

http://www.antonine-education.co.uk/Image_library/Physics_1/Particles/force_graph.JPG

[CarlJoseph]

Forces at this scale are called van der Waal forces. The repulsive force is due to the Pauli exclusion principle and electron degeneracy pressure (http://astronomy.swin.edu.au/cosmos/E/electron+degeneracy+pressure). Perhaps that's what you're thinking of?

[sjastro]

What has this got to with gravity?

Your link refers refers to the electrostatic (Coulomb force) between a positively and negatively charged atom which form an ionic bond. (https://en.wikipedia.org/wiki/Ionic_bonding)
Bring the atoms in closer and the electrons from each atom repel each other. The zero point for force occurs when the repulsive force equals the attractive force. The magnitude of the attractive force is at a maximum when the repulsion force is at a minimum. Separate the atoms further and the Coulomb force decreases as the inverse square law for distance.

[Eratosthenes]

:thumbsup: indeed Afro Boy.....

time for some Calypsonians from the Taj

https://www.youtube.com/watch?v=UFh46LvV1DQ

[sjastro]

Yeah sure you were thinking of electron degeneracy pressure and van der Waal forces.:rofl:
Strange how your link tells a totally different picture.
http://www.antonine-education.co.uk/...orce_graph.JPG

Since you find Physics relativity simple you should be able to answer the following questions.

(1) Why does the zero force point of the graph occur at an atomic radius scale and not at a molecular scale as one would expect for van der Vaal forces?
(2) Why does the force reach an asymptotic value as the distance approaches zero given that electron degeneracy pressure essentially makes an atom "incompressible" and therefore impossible to approach "small" distances?

[bojan]

Check this:
emergent gravity or superposition of states?
Looks like cat can't be dead AND alive after all :P

http://www.scientificamerican.com/article/gravity-kills-schroedinger-s-cat/?WT.mc_id=SA_WR_20150624

http://physicsworld.com/cws/article/news/2015/jun/19/does-time-dilation-destroy-quantum-superposition

[AlexN]

I know I've experienced superposition a few times in a very classical way.

I believe that a usb plugs initial state is a superposition. Every time I plug a usb lead into a computer (without looking first. Observation causes decoherance) it is upside down, so I flip it over, try again.. Still won't plug in. So I take a look, flip it back to the original orientation and wouldn't you know it, Goes in fine when earlier in the same orientation it wouldn't.

This tells me that prior to observation the usb plug is both right side up and upside down at the same time. Only after direct observation does the quantum superposition become decoherant and it falls back to a classical state.

That's quantum mechanics interacting with every day life on a large scale object despite the presence of gravity.

#nomathematicsrequired

[rustigsmed]

:lol: