Why does mass curve space-time?

[ajb]

As for the other i like string theory for some reason I still cant figure out why tho.

 

The big thing about string theory is that it necessarily includes the graviton in its spectra. So, string theory seems to be the only finite perturbatative theory of quantum gravity. Exactly to what extent this truly is a quantum theory of gravity is debatable, but it does include the necessary fundamental degrees of freedom.

 

Thank you for showing how Experts should reply.

 

Thank you.

[Brainteaserfan]

PI,

 

Sometimes the why comes out and sometimes it doesn't. Is there a why [math]\pi[/math] is the value it is? Maybe, but that doesn't hamper its usefulness. The why can be an interesting question, but it doesn't ruin or invalidate the physics or math. The why isn't really the answer that physicist are looking for; physics is about making mathematical predictions of what nature will do. If I drop this block weighing 1 kg from the height of my head, what speed will it hit the ground? If a sun has a certain composition of elements, what temperature is its corona? On what date will the next solar eclipse be? Etc.

 

Physics doesn't try to answer the why behind these questions, so the why is often out of scope. It may be that we never find out the why space-time gets warped, but we should still nonetheless be able to make predictions about what effects is has on objects. If the predictions are accurate, that is all it needs to be a success in the eyes of physics.

 

Yes, if there is no why it can be useful, but remember, people thought everything went around the Earth too, and they predicted many things accurately. IMO, Why's are the most important part

[papenoir]

I think Jacques has the right answer: mass "eats" space around it.

 

The dimension mass interact with dimension space-time in a way that it "leaks-out" or "delete" space-time in a steady rate.

Think of spreadsheet as space-time, a photon travels from cell to cell at constant speed c. A mass is an interaction (string or cord) from space-time dimension to the mass dimension, in a way that it delete one cell every given time.

In a spreadsheet, when you delete a cell, all other cells are shifted instantaneously. The same effect happens in space-time dimension: a space deleted by a mass affect the whole univers instantaneously: that's the force of gravity.

When a critical mass is located at the same area, it "deletes" space at such a rate, that even mass-less photon can not escape from it. It's like the cells are deleted at the same rate as the speed of light moves from cell to cell.

 

When an object/satelite rotates around a big mass, supposedly it's momentum takes him on a straight line, but since the space between him and the big mass disapear at a constant rate, the satelite takes a circular trajectory. That's the gravitational force at work. In fact the satelite travels on a straight line, but it's the space that warps around.

 

Two motionless objects in an empty space will find the space between them disapearing at a constant rate, and they'll end up closer to each other (at the rate proportional to the product of their masses).

 

When we move at a certain speed near a big mass, one cell at a time like in a spreadsheet, the spaces deleted by the mass make us think that the time is slower, like if we play monopoly or other board game, and the place behind us is deleted. We rolled 6, and moved 6 places but it ends up only 5 places from where we were. The time to make a round seems longer. That's the relativity of time that turns slower near a big mass.

 

If G is around 6.6 10E-16 cm3 g-1 s-2, then each gram of mass deletes approximately 2.56 E-8 cm3 per seconds.

 

It's papenoir's theory, any comment is welcome.

[hawksmere]

OK, i think i have finally understood the question : ) So there is an obvious difference between Euclidean space and Minowski's spacetime which is of course curved rather than flat (respectively). So the minus sign must apply as pythagoras' theorem cannot. just as on earth where distance (usually the shortest) is curved in line with the formation of our sphere. However Minowskis' spacetime doesn't always satisfy S²=(ct)² - X² which means that is curves always in the same way (as on earth).

 

As the earth (staying with a spherical example) is not compeltely round (mountains, rivers, terrain etc) what happens to the curve when travelling through undulating surface changes? As with space itself, one has to consider gravity influences as influences of gravity alsy bend spacetime. The example with using a torch in a life is a good one. You can also consider double pulsars which say are two nuetron stars at a distance of around 1 million kilometres. Each having the mass of the sun ,compressed into say the size of a city spinning thousands of times a second and careering around each other at a distance 75,000 miles. Einstien tested that the radio waves from one of them sometimes passed very close to the the other pulsars. meaning that ultraregular radio beams pass through a region of veryheavy curved time which of course will naturally delay its transit. This providing evidence of spacetime being curved as a direct incluence.

 

How mass curves space time?or in the case of the earth (a spherical body of mass) .

In order to calculate mass effects one needs know the ratio volume/surface of the closed volume that produces the spacetime curvature and e_v.

 

I asked the same question and my answer to this was my question in another.

 

http://www.scienceforums.net/topic/59310-warping-space-time/

Edited September 12, 2011 by hawksmere

[ajb]

So there is an obvious difference between Euclidean space and Minowski's spacetime which is of course curved rather than flat (respectively).

 

No, both Minkowski and Euclidean space are flat.

 

 

So the minus sign must apply as pythagoras' theorem cannot.

 

Right, the extra minus sign for Minkowski space should indeed be thought of as a generalisation of the Pythagoras' theorem. The space is still technically flat, but we lose the positive definite property of "distance". Meaning we can have in effect "lengths" that are negative, zero or positive.

 

just as on earth where distance (usually the shortest) is curved in line with the formation of our sphere.

 

Right, thegreat circles.

 

However Minowskis' spacetime doesn't always satisfy S²=(ct)² - X² which means that is curves always in the same way (as on earth).

 

[math](ds)^{2} = (c\: dt)^{2}- (dx)^{2}[/math]

 

is the definition of the "distance" between two (near by) points on Minkowski space. (You can then integrate this along a path. )

 

What one is interested in is the geodesics, that is the paths that minimize this "distance", which is usually refereed to as space-time interval. (I have been a bit slack here, we can fill in details later)

[sci-curious]

Interesting thread. I came to it and this forum because I wanted to know if the question ( 'WHY or HOW mass/energy curves space-time?') had ever been answered. And, it appears not, though this is only the beginning of my search.

I'd just watched a fascinating talk by Noam Chomsky, which amazingly had nothing to do with politics. He addresses the limits of human knowledge and discovery and concludes that what we know of nature, which - though quite 'useful' to us - is nontheless only a fraction of 'reality' and that there are certain 'things' we will never understand because it is simply outside our capacity. Kind of like we'll never be able to 'see' 4 + dimensions of space.

I immediately objected and siezed upon the fact that Einstien explained what gravity 'is' after Newton explained what gravity 'does'. Newton left the former question in the hands of God and was convinced it was unknowable. He didn't or couldn't anticipate General Relativity. But, now that we know what gravity does and what it is: the curvature of space-time by energy/mass. The next question, 'why does space time react thus in the presence of mass/energy?'; tries to dig a bit deeper.

And so, I wonder if this is one of those things that falls outside the capacity of human understanding, knowledge, discovery etc.

Then again maybe the answer is as simple as imagining someone pushing there way into a crowded elevator. Their very presence upsets or warps the configuration of passengers already present. (!?) But then the question becomes what is the 'fabric' of space-time or, sticking with the metaphor, who/what are the 'passengers'?

[abisha]

I think the question is irrelevant, when the human brain can't comprehend the answer.

a person studied in this field, can understand terms and formula's, they can even draw you a picture how a body wraps space and time

But when it comes to explain the "true reality" their brain gets locked.

 

it's like a dog try to understand how a airplane can fly, we simply not yet ready for it.

[Dekan]

it's like a dog try to understand how a airplane can fly, we simply not yet ready for it.

It's like the Giant Rat of Sumatra, the world is not yet ready for it Watson.

[safesphere]

The question is legit. The answer exists, but has not yet been published. Spacetime is not exactly what you have been taught. There is indeed a reason a certain type of energy, including mass, slows down time and we see it as if space is curved. The reason of course has to do with the fact that time and energy are two sides of the same Fourier pair. Hiwever, this fact alone does not explain the WHY or HOW. There is a bit more to it. This is all I have a liberty to say right now.

[krash661]

here's something i just found that's interesting,

 

I do not know if it's accurate or such,

I have not been through it yet, just found it.

 

International Society for the Advanced Study of Spacetime

http://www.spacetimesociety.org/minkowski.html

[PureGenius]

Mass is trapped within an electromagnetic field in almost all instants without motion there wouldn't b any inherent effect on space time around a static object now if an object is accelerated in any direction then the space time begins to shift into a potential time effect Ie the time dilation thus the velocity of time flow is increased therefore the mass of the object increases the electromagnetic freqeuncy into a higher energy state were time flow is reduced this alteration of the time flow the effect is described in your qestion. Bassically time is modulated through the electromagnetic field space is curved by the strength ie potential field of that object repelling the forces in the universe that cause the current speed of time .

[ydoaPs]

!

Moderator Note

Personal speculations are reserved for the Speculations section. The Physics section is for mainstream physics only. As such, speculations are off-topic. If you wish to discuss your theory, feel free to start a thread in the Speculations section.

[metacogitans]

I found this thread while googling to see if anyone had came up with the answer to the thread's question before me.

I have a very simple but entirely plausible explanation as to why mass dilates space-time if we can assume the following:

- 'Spacetime' itself must consist of something, and this backbone of space-time is physically present among everything else residing in it.

- Since, simply put, two things can not occupy the same exact location simultaneously, then matter with intrinsic mass and it's own self-maintained volume pushes whatever makes up space-time out of the way. When considering a large quantity of mass on the scale of a planet or star in this regard, we can account for the curvature of space-time and the phenomenon of gravity.

 

To further illustrate my point, imagine space-time as an x,y,z coordinate grid; now imagine a particle as a sphere at the point (0,0,0) on this coordinate grid. However, the grid does not lay on top of the sphere overlapping it; but is warped around the sphere. Now, imagine many spheres, and the effect they have on the surrounding grid. What it starts to resemble is identical to the phenomenon of curved space-time described in general relativity.

 

Another analogy: imagine we plop a boat into a lake. The water of the lake moves out of the way of the boat as it is plopped in. The boat represents a particle with mass, and the water of the lake represents whatever it is which makes up the backbone of space-time.

 

So there you have it, an entirely sensible explanation. Although I couldn't begin to tell you what this backbone of space-time is made out of, I can at least assume that it is physically present among the other contents of the universe and interacts with them.

 

To put it in just one sentence: the curvature of spacetime resulting from the presence of mass is a geometrical consequence of the inherent nature of mass occupying volume.

 

Also, I've got a link to a good PDF that really helps one visualize the dilation of space-time in a gravity-well and the breakdown of Euclidean geometry in General Relativity; it points out that the diameter of the sun is many kilometers greater than what we would expect if we took the sun's circumference divided by pi, due to the dilation of space-time towards the center of the sun. It also uses existing widely-accepted equations in physics (such as actually using the Einstein field equations, for example), so it should appease those who want all conclusions to be backed up with hard math. http://www.johnstonsarchive.net/relativity/stcurve.pdf

Edited June 29, 2014 by metacogitans

[Mordred]

good article however its too bad you didn't pay attention to the details....

 

look at equation 1

 

here is the quote describing equation 1

 

"where G is the Einstein curvature tensor,T is the stress-energy tensor,G is the gravitational constant, and c is the speed of light. The Einstein tcnsor
describes the curvature of space-time; the stress-energy tensor describes the density of mass-energy. This equation therefore concisely describes the curvature
of space-time that results from the presence of mass-energy. This curvature in turn determines the motion of freely falling objects"

 

please note the stress energy tensor is the density of mass energy, in other words if you take the mass of the Earth and reduce its volume below its Schwartzchild radius it will become a black hole. Or if you have an object with the same volume as the Earth but higher density it will exert a greater gravitational influence.

 

this wiki page gives the Schwartzchild radius for the Earth roughly the size of a peanut 9 mm

http://en.wikipedia.org/wiki/Schwarzschild_radius

 

here is some more information on the stress energy tenser

http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor

 

please note line

"In general relativity, the symmetric stress–energy tensor acts as the source of space-time curvature"

 

by the way your fluid analogy isn't a bad idea, its just a bit more complicated than mere volume. (its due to energy-density relations) You will notice the terms perfect fluid being used numerous times on the stress energy tenser page.

 

see the last link for the fluid solutions of the Einstein field equations

"In general relativity, a fluid solution is an exact solution of the Einstein field equation in which the gravitational field is produced entirely by the mass, momentum, and stress density of a fluid."

 

http://en.wikipedia.org/wiki/Fluid_solution

 

by the way welcome to the forum

 

here this reference will help you learn GR, careful though its 927 pages long (page 167 covers the fluid dynamics)

 

http://www.blau.itp.unibe.ch/newlecturesGR.pdf

 

here is another reference for GR fluid dynamics

http://www.nikhef.nl/~t32/relhyd.pdf Relativistic fluid dynamics

Edited June 29, 2014 by Mordred

[metacogitans]

 

 

good article however its too bad you didn't pay attention to the details....

 

look at equation 1

 

here is the quote describing equation 1

 

"where G is the Einstein curvature tensor,T is the stress-energy tensor,G is the gravitational constant, and c is the speed of light. The Einstein tcnsor

describes the curvature of space-time; the stress-energy tensor describes the density of mass-energy. This equation therefore concisely describes the curvature

of space-time that results from the presence of mass-energy. This curvature in turn determines the motion of freely falling objects"

 

please note the stress energy tensor is the density of mass energy, in other words if you take the mass of the Earth and reduce its volume below its Schwartzchild radius it will become a black hole. Or if you have an object with the same volume as the Earth but higher density it will exert a greater gravitational influence.

 

this wiki page gives the Schwartzchild radius for the Earth roughly the size of a peanut 9 mm

http://en.wikipedia.org/wiki/Schwarzschild_radius

 

here is some more information on the stress energy tenser

http://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor

 

please note line

"In general relativity, the symmetric stress–energy tensor acts as the source of space-time curvature"

 

by the way your fluid analogy isn't a bad idea, its just a bit more complicated than mere volume. (its due to energy-density relations) You will notice the terms perfect fluid being used numerous times on the stress energy tenser page.

 

see the last link for the fluid solutions of the Einstein field equations

"In general relativity, a fluid solution is an exact solution of the Einstein field equation in which the gravitational field is produced entirely by the mass, momentum, and stress density of a fluid."

 

http://en.wikipedia.org/wiki/Fluid_solution

 

by the way welcome to the forum

 

here this reference will help you learn GR, careful though its 927 pages long (page 167 covers the fluid dynamics)

 

http://www.blau.itp.unibe.ch/newlecturesGR.pdf

 

here is another reference for GR fluid dynamics

http://www.nikhef.nl/~t32/relhyd.pdf Relativistic fluid dynamics

Thanks; didn't want to try giving a technically accurate explanation - what I know about the math of Einstein's field equation comes from what I remember from this video:

To be honest, the math involving the tensors in Einstein's field equations is a little bit over my head; I understand the role each piece of the equation has and can follow a person as they work through it, but I wouldn't be able to use it myself. I actually just started trying to learn the math of GR just a few days ago. The last math class I took was precalc and since then I've had to teach myself calculus and trig, so my knowledge of mathematics probably isn't as comprehensive as it should be before dabbling in things like General Relativity - but, it interests me, so I'm taking a swing at it.

Edited June 29, 2014 by metacogitans

[Mordred]

no problem, always good to see someone interested in learning the mathematics. for differential geometry a good reference is "Elementary differential geometry" by O'Niel

 

http://www.amazon.com/Elementary-Differential-Geometry-Revised-Edition/dp/0120887355

 

you will find the above references a bit tricky as they both heavily involve differential geometry however they will be good references for later on.

 

Another good textbook aid is "Roads to Reality" by Roger Penrose its not specifically GR but its a good aid in understanding the mathematics of differential geometry in regards to the various physics fields.

http://www.goodreads.com/book/show/10638.The_Road_to_Reality

 

an excellent textbook on general relativity is Wald's "General Relativity"

http://www.amazon.com/General-Relativity-Robert-M-Wald/dp/0226870332

 

this is a very basic entry level article its a reprint of Einsteins paper (its metrics are fairly simple so should get you started

http://www.gutenberg.org/files/30155/30155-pdf.pdf: "Relativity: The Special and General Theory" by Albert Einstein

 

just in case you can't afford the textbooks here is another useful article (238 pages) free textbook style

Lecture Notes on General Relativity
Sean M. Carroll

http://arxiv.org/pdf/gr-qc/9712019.pdf

 

unfortunately relativity does require decent math skills, so I would look for good textbooks and articles covering differential geometry and be patient (keep at it)

 

forgot to add one of the better low mathematic (to start with) textbooks to understand GR, I've read is

"A First Course in General Relativity" by Bernard Schultz

http://www.amazon.co.uk/First-Course-General-Relativity/dp/0521887054

 

here is a good introductory paper much like the last book I mentioned

http://www.math.ist.utl.pt/~jnatar/RM-12/Geom_Rel.pdf General Relativity Without Calculus

Edited June 29, 2014 by Mordred

[metacogitans]

Yeah I don't have money for books; I've been sneaking in lectures on youtube from Caltech, MIT, and Stanford, and downloading any free PDFs on the subject I find

Edited June 29, 2014 by metacogitans

[Mordred]

thought so you'll find the last link handy its a good introductory level article (algebra based)

[aaa16797]

Well, my guess would be that matter is made of compressed spacetime, so there's less spacetime to go around nearby matter. Of course that's just random gibberish until someone finds an equation that would describe such and checks that the predictions are correct. Is that the sort of "why?" that you were looking for? Because if you were looking for a "why?" that would not involve new equations, the sort of question that Newton thought irrelevant to his idea of gravity, then science isn't really the place to look for such answers.

Well actually I agree with Mr Skeptic but in another way...doesn't any object with a higher mass have a higher density? And obviously dense objects sink, causing the bends in space-time which is why the planets with more density or mass would have more gravity. This is not a topic i have dwelved too much into but i am just using logic to prove this.

[Mordred]

not necessarily, you can have two objects with the same mass, but different volume. Take a simple example a 1 kg lead ball vs a 1kg ball of aluminum. The aluminum ball will have a greater volume. The lead ball has a higher mass density

[aaa16797]

I'm just saying that all planets that do have a density greater than 0 will bend space time

[Strange]

I'm just saying that all planets that do have a density greater than 0 will bend space time

 

But that is because of their mass. (They obviously have non-zero density as well, but that is also a consequence of their mass.)

[aaa16797]

 

But that is because of their mass. (They obviously have non-zero density as well, but that is also a consequence of their mass.)

yeah, so thats why mass curves space time . thats what i have been saying

[Kairat]

Space is three dimensional.

Matter is four dimensional. The fourth dimesnion is time.

So the matter is moving along it's fourth dimension (i.e. time) through space and interacts with it causing it to curve.

Mass is a kind of viscosity coefficient. The more massive a body is, the slower time passes.

If we continue to increase the mass of a body time will stop at some point and we get a black hole.

[swansont]

 

Mass is a kind of viscosity coefficient. The more massive a body is, the slower time passes.

If we continue to increase the mass of a body time will stop at some point and we get a black hole.

 

No, not really. It's not that simple. Time dilation depends on the gravitational potential. It's possible a body with a larger mass could have a smaller time dilation effect.