[ 3 / biz / cgl / ck / diy / fa / ic / jp / lit / sci / vr / vt ] [ index / top / reports ] [ become a patron ] [ status ]
2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

View post   
File: 30 KB, 516x387, spacetime.jpg [View same] [iqdb] [saucenao] [google]
7607125 No.7607125 [Reply] [Original]

How does spacetime being warped lead to the effect of gravity?

>> No.7607131

>>7607125
We know there's some kind of relationship between gravity and warped spacetime. That's about it.

>> No.7607138

what do you mean by warped? can't any force be called a result of "spacetime"?

>> No.7607150

>>7607138
Wow ur stupid

>> No.7607151

>>7607125
Warped spacetime is gravity

>> No.7607162

>>7607151
how does the warp make an apple fall from the tree, I think, is the question.

>> No.7607166

>>7607162
something like that
in all the demonstrations like in the pic, they show how an object moving in a straight line is made to curve by the warped spacetime

but what about 2 objects near eachother, but at rest?

>> No.7607169

>>7607166
Its like a ripple effect, they'll cross paths and still affect everything around them together and seperate

>> No.7607174

>>7607150
in what way? I'm not trying to be snarky i just don't know much about theoretical physics

>> No.7607186

>>7607174
Spacetime is like the 3d plane we are living on, some people believe that one 2d part is warped or bent by force to create gravity, so me pushing you forward wouldn't have anything to do with a "result of spacetime" you wouldnt really be changing the 2 or 3d plane in any way other than the gravity warping you down to stay attached to the earth

>> No.7607200

>>7607174
We don't know exactly how gravity works still but the general consensus is that it causes spacetime to warp. How it does that we don't know but objects with lesser mass are drawn towards objects with greater mass because an object with greater mass warps space more.

Imagine a sheet of plastic over your kitchen sink, if you set an orange on it what happens? The sheet gets stretched and warped right? And if you set a grape in there what do you think its gonna do? Roll down towards the orange. We're all attracted to the earth because its more massive and the earth is attracted to the sun because its more massive. That's the basic idea but we still don't know allot.

>> No.7607203

>>7607186
>>7607200
so the difference between gravity and "any old force" is that gravity's relationship with spacetime goes both ways? what's the OP question asking then?

>> No.7607206

>>7607203
Not really sure, he's basically asking if the theory is real, like how the fuck do we answer that, any old force is basically not constant as well while gravity is always there, on everything, anything can have a orbit if heavy enough with light enough stuff around you

>> No.7607210

>>7607200
>Imagine a sheet of plastic over your kitchen sink, if you set an orange on it what happens? >The sheet gets stretched and warped right? And if you set a grape in there what do you think its gonna do? Roll down towards the orange.

that is an utterly useless example, the grape rolls toward the orange BECAUSE OF GRAVITY.

>objects with lesser mass are drawn towards objects with greater mass because an object with greater mass warps space more.

objects with greater mass are also drawn towards objects with lesser mass. lrn23rdlawofmotion

>> No.7607218
File: 107 KB, 500x280, 2545431.jpg [View same] [iqdb] [saucenao] [google]
7607218

>> No.7607220

>>7607210
Because of gravity... Yes that's what were fucking explaining, take the gravity out of the real world and the grape can't sit stable on the bent space time plane you fucking degenerate

>> No.7607222

>>7607206
undoubtedly an oversimplification and i'm admittedly not in the field of physics, but that sounds like space-time warping is just a macrocosm of gravity

>> No.7607230

>>7607210
Just trying to give a simple explanation brah. Seemed like he just wanted to know why shit falls towards the earth/why the earth orbits the sun.

Sun is the most massive thing in the solar system so all the other planets are drawn towards it, like the grape rolling towards the orange.

>> No.7607232

>>7607222
Then what is gravity? To cause spacetime to warp but nothing else can cause it to warp, you're thinking in the opposite direction

>> No.7607244

>>7607232
i don't think the fifth dimensionality can be verbalized, especially by someone who doesn't know all of the lingo, but the relationship between gravity and space-time could be analogous to space-time's relationship with a greater concept (probability?). that'd be my first totally unscientific guess

>> No.7607246

>>7607125
This is pretty simplified, and doesn't really explain much, but...

In ordinary flat spacetime, matter moves in straight lines through space and time, right?

Well, because spacetime is curved, matter moves in curved paths through space and time.

This creates the effect of gravity, which does the same thing: In the absence of gravity (and other forces) particles would always move in straight lines at constant velocity, whereas in the presence of gravity their paths curve.

(It's the path through space-time that matters specifically; two objects at rest and then accelerating towards each other in space is the same thing as their paths through space-time being parallel and then curving towards each other).

The curvature of spacetime creates the effects of gravity. In fact, a curved-spacetime theory theory of regular Newtonian gravity can be easily constructed.

The reason people came up with "curved spacetime" as an explanation is that it provides a nice way to extend the principle of relativity -in special relativity all velocities and positions are relative, but accelerations are still absolute. General relativity, with its curved spacetime, provides a way to make gravitational acceleration relative as well.

>> No.7607248

>>7607166
what are binary systems for $5?

>> No.7607252

>>7607244
I wasn't asking what gravity was I was replying to him in a sarcastic manner

>> No.7607253

>>7607186
all three dimensions get warped to a point in the center of the massive object they just use 2D planes to give a visual representation that is acceptable and understandable for lamens

>> No.7607254

>>7607246
>two objects at rest and then accelerating towards each other in space is the same thing as

y do they move at all?

>> No.7607260

>>7607254
i.e. why don't they just stay where they are?
why does "warped space time" lead to movement?

>> No.7607264

>>7607253
Yea its hard to imagine warped 3d space. A warped 2d plane and how it effects movement is much easier to visualize.

>> No.7607268

>>7607253
so, density?

>> No.7607273

>>7607162
Matter is vacuum energy condensed into shapes and shit.
Space/time is stretched from its neutral position as a field and pulls on other things that have pull (things with mass i.e. matter).
It's kinda liquid-y.

>> No.7607274

>>7607264
basically around a dense or high mass body, space time condenses around it to create higher local time rates and compressed distances relative to stich spacetime outside of the effects of the warp. that's why the theory that near an event horizon you'll get time dilation.

think of spacetime as a series of cubes, high mass. odes make those cubes squish together creating higher "density" spacetime for lack of better vocabulary at my disposal.
this causes a pull and the well effect until a hard point is reached at the gravitational center or center of mass

>> No.7607276

>>7607246
Trying to explain this a little better -

The principle of relativity tells us, basically, that if we are in a closed box with no way of looking at the outside world, we should be able to tell as little as possible about what's actually going on outside the box by conducting experiments inside the box.

In special relativity, and ordinary Newtonian mechanics, that's true of position and velocity: There is no way, inside the box, to tell whether you're standing still or moving at a constant velocity.

But add gravity into the picture, and there's one more thing that's relative, too-

There is no way to tell between either of those two things above (rest or constant velocity), or if you're in freefall under gravitational acceleration.

In fact, this is very important: The people in the Space Station are actually still under the effect of a gravitational force from the Earth almost as strong as we are under down here. They're not that much further from Earth than we are. The Space Station is in zero gravity because it's in freefall.

So we know that, in the absence of any applied force, objects trace straight-line paths through space-time. (Even if you're stationary, you're still tracing a straight-line path: specifically, straight parallel to the time axis)

And not only does this "generalized principle of relativity" tell us that perhaps there's no fundamental difference between travelling in freefall or at a constant velocity, but these free-fall paths display other characteristics of ordinary straight-line paths in zero gravity: For instance, it requires you to apply a force to deviate from the path, and then you stay on a new path.

But, if we place two "test particles", going the same velocity, in infinitesimally different locations, under the influence of gravity, then their paths will diverge - slowly, the distance between them will increase. If we take these paths to be straight lines, this is the definition of curved space.

>> No.7607278

>>7607274
stoich not stich fucking autocorrect

>> No.7607283

>>7607274
>>7607276

Good descriptions.

>> No.7607285

>>7607260
Because space-TIME is curved.

Even if you're both at rest relative to each other in space, you're both still moving through time - at one second* per second**, to be specific.

Because space-*Time* is curved, objects within it trace curved paths through spacetime. This causes the paths of the two objects - which are initially parallel, to each other and to the "time axis" at t=0 - to gradually curve away from the time axis and start travelling towards each other in the space axis.

*of proper time
**of coordinate time

>> No.7607290

>>7607283
thanks :3
also a deeper explanation fo the event horizon description is if you travel in a straight line at a constant linear velocity, and pass near and event horizon you technically travel through more space time along that linear path near the event horizon which is why the dilation effect occurs, linear distance is constant but due to the compression of spacetime you've traveled through more than your linear distance

>> No.7607295

does gravity pull stuff together, or is vacuum pushing everything together? if the vacuum is pushing everything together that would explain why the universe is expanding. But I'm not 100% certain they're right about the universe expanding. We only think so cause of red shift in distant stars. But that could just be gravitational drag on photons over extreme distances slowing the light down.

>> No.7607299

>>7607276
Incidentally, the very next question you might ask is "Could we use this to explain *all* the different fields? Is the electric field also curvature somehow?"

Good question! My answer is
"Mathematically, yes, though you need an extra dimension to give it a second axis to curve along, and in order to get rid of it to produce the 3+1 dimensional world we appear to see you have to do something like rolling it up into a tiny closed circle instead of an infinite axis. Now you know why String Theory has so many rolled-up extra dimensions."

>> No.7607300

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.youtube.com/watch%3Fv%3D8bTdMmNZm2M&ved=0CB4QyCkwAGoVChMIseXO9_jUyAIVjG0-Ch3ZdwZR&usg=AFQjCNFyUOqJxcd0ky85VrprCFkE49znDw

Objects with more mass don't attract other objects more, they just move less relative to everything else because of inertia. Watch the video

>> No.7607354

>>7607285
thank you
this answer gives me some satisfaction

>> No.7607367
File: 65 KB, 566x480, Read A Book.jpg [View same] [iqdb] [saucenao] [google]
7607367

>>7607295
Just read a book, m8. These are some well-answered and explained questions that you should seek the answers to on your own.
Get a look. It's in a book. Stop being a faggot.

>> No.7607374

>>7607354
http://ls.poly.edu/~jbain/philrel/philrellectures/09.Geometrization.pdf

>> No.7607391

>>7607162
For the same reason that an apple would roll down a hill

>> No.7607393

>>7607125
Not done a full course in general relativity yet, but from what I understand, you can't really picture it like this image. Spacetime is not a grid, it is a lattice (not a 2d plane getting warped like this picture, but a 3d lattice getting warped). The big waddafuq ia why gravity is always attractive and other forces have kind of "opposites".

>> No.7607396

>>7607393
You can just think of this 2d picture overlapping around the earth infidecimaly, it will seem like a 3d bend in space time

>> No.7607397

Imagine throwing a ball. Viewed from above the ball travels in a straight line. From the side the ball travels on a curve.

What Einstein realized is that the curve is supposed to be a straight line as well just as when viewed from above. Thus, spacetime is curved and everything is moving along the straightest paths in the curved spacetime.

>> No.7607401

>>7607299
Also, there's an important sense in which gravity and other forces are distinct.

Gravity/spacetime curvature is truly universal - it acts on all objects with mass, energy, or momentum, which is to say, *everything*. Everything couples to gravity, because everything exists in spacetime.

Meanwhile, all other forces only act on certain kinds of things, which have properties we call "charges:" Electric charge, weak isospin, and color charge.

>> No.7607415

>>7607393
I suspect that the answer lies in the origin of inertia.

Nobody has ever, to my understanding, satisfactorily explained why mass/energy resists being accelerated; it's simply taken for granted.

And accelerations are bizarrely non-relative: the inertial forces created by being in an accelerating reference frame mean that it IS possible to tell if you're "really" accelerating or not. While there is no absolute position or velocity, there is absolute acceleration. This seems odd.

There is nothing in the structure of general relativity that demands mass be positive, but it does require that gravitational mass always equal inertial mass. If the mysterious origin of inertia demands that inertia always be positive, then this would in turn cause gravitational force to always be positive.

>> No.7607429

>>7607415
I have pleb understanding of gr so maybe I'm way off base here but isn't it technically incorrect to say there is "absolute" acceleration because of the equivalence principal?

As I understood it there should be no way to tell the difference between being in a box being pulled up accelerating 32 ft per second (or whatever the rate is gravity pulls stuff down at on earth) and being within earths gravitational field at "rest".

I might just be massively misunderstanding something though like I said pleb here.

>> No.7607433

>>7607246
>whereas in the presence of gravity their paths curve.
Isn't is also possible that their paths aren't curved at all, but the warp in space time just gives the illusion ( and from our perspective, the experience ) of an objects path curving?
Like if you draw a straight line on a paper, but the line stops being straight when you distort the paper by bending or twisting it.

>> No.7607440

>>7607433
In this case though the "illusion" would effectively be reality.

Think of it this way, even if that line you drew only curves because the paper is curved if you still measure it to be curved and in all ways it behaves as a curved line isn't that the same as it just being curved? Does the distinction between straight line curved paper and curved line even mean anything at that point?

>> No.7608196

>>7607200
The grape rolls down because of gravity.

>> No.7608265

>>7607131
>>7607285
I think the hardest thing to get your head around when talking about gravity is that space and time are considered the same thing, it's so weird.

>> No.7608357

>>7608265
It's actually really easy to understand that if you start with Special Relativity, which doesn't have gravity.

>> No.7608890

I think it's because space-time is 4-dimensional, one of them being time. Meaning, you can't ever stay still in spacetime.

>> No.7608938

>>7607125
In general relativity, gravity doesn't exist as a force. Rather, it is posited that all things travel on geodesics of the spacetime. These geodesics are lines that keep their own tangent vectors constant with relation to themselves, and extremize their length (in lorentzian [i.e relativistic] spacetimes you can always find paths that are minimal, and on e.g a rimannian sphere you can find paths that are maximal).

Now in the calculations for a geodesic there is something called a metric of space. The metric of space let's you calculate the length of an infinisetimal tangent vector, which you can integrate along a path to get that path's length. This metric describes curvature in the sense that some metrics will deviate from the eucledian metric diag(1,1,1) .

Einstein's equation puts the Rimannian curvature tensor (which is only 0 or a flat eucledian metric) in relation to the energy-momentum tensor which describes your matter and energy density. We solve for a metric by using Einstein's equation.

For example the Schwartzschild metric describes the length of a tangent vector around a spherical, static body. The friedmann metric describes the length in an expanding, isotropic and homogeneous universe.

Now we said that there is no gravity but only movement on geodesics. For example, in the orbit of a star, a planet in orbit will be force free. However the curvature of space due to the star will make the planet travel on geodesics that circle the star spatially. This is what is meant by the bending of space time.

>> No.7608975

>>7608938
To expand on the idea of curvature:

Curvature is often explained as the failure of tangent vectors to return to their initial direction after being moved around a closed path (in fact if you calculate the change of direction of a vector across a infinitesimal loop, you'll find the equation explciitely contains the Riemann curvature tensor).

Imagine you're standing on the north pole of a sphere and your arm point in an arbitrary direction (your arm is the tangent vector). Now you scuttle side-stepping down to the equator of that sphere (always keeping your arm pointed in the same direction relative to your body). Then you walk about a quarter of its length across the equator and then you scuttle side-stepping back up to the north pole. Around this path, the direction of your arm will have turned by 90 degrees. Similarly, on any 'curved' surface the direction of the tangent vector (arm) will generally change. The only exception is the 'flat' eucledian plane, where any closed path will yield the original direction at the end. In fact, the Riemann curvature tensor is 0 on the eucledian plane.

>> No.7609450

>>7608938
>>7608975
Is there anything that would help a dummy like me grasp this better?

>> No.7609459

>>7609450
You can imagine how a warped 2d plane would effect the movement of objects on it for a very simple explanation, its not technically correct but kinda gives you the idea.

>> No.7609474

Scientists basically admit they cant account for 96% of the known universe since there is no way to measure it. The biggest problem for physicists is that the Sun and Galaxy itself doesn't have enough mass to keep it together and energy to account for its expansion since the big bang it should have reversed and collapsed the universe in a long time ago. Something unknown is keeping everything afloat in space yet spreading new previously seemingly uncreated space in therefrom Nothing at all. No way to measure it only calculation is that it is there. The current physics model is admittedly flawed by this discovery yet nobody has any answers. If this is not the most Paranormal discovery in the last Century then i dont know what paranormal even means. Just like in Quantum physics we cant account for the unexplained so in Celestial mechanics scale we cannot account for the unexplained.

>> No.7609482

>>7607125
its all about what a straight vector is in curved space time.

if you think about it, the ISS is going in a straight vector at a relevantly constant speed, hence you observe no force and things "float" its an inertial frame of reference, its not accelerating.

which means its moving in a straight line (in sapce time) but the earth is warping space time such that a straight line is actually an orbit.

On the earth the ground is accelerating upwards toward us because of this warping of space time.

its kinda wonky and we don't fully understand it, but in most applications gravity can be thought of and treated like a Newtonian force.

>> No.7609522
File: 325 KB, 498x574, PRIP.95094505.15.2.gif [View same] [iqdb] [saucenao] [google]
7609522

>>7608265

Are they really the same thing or are they just linked ?

I think they are just linked.

>> No.7609644

>>7608357
Is this true at the speed of light?
A photon doesn't seem to experience the dimensions.

I have a question for the physicists.
299 792 458 m / s
Why this number? whats special about it?
Surely that number is telling us something. How does it tie in with the rest of the universe?
If light is travelling in a wave of probability, what happens when you make the wave shorter? Are there any limits to how short you can make a wavelength? Or how much you can red shift it? Would it eventually become just a perfect straight line?

>> No.7609669

>>7609644
I don't think I can answer all that but

>299 792 458 m / s Why this number?

Are you saying why is that the max speed of light and not some other speed? No one knows. That's like asking why the universe is how it is and not something else.

>> No.7609685

>>7609669
I understand If you multiply the wavelength by the frequency of any EM wave it will always equal c.
I'm wondering why this number is so significant and how it relates to our understanding of the universe

>> No.7609699

>>7609685
>how it relates to our understanding

Its the universal speed limit, and having a speed limit is important because it preserves causality across different frames of reference.

>> No.7609918

299 792 458 m / s
Why?

>> No.7609934

>>7609918
That is how fast we observe light to be. I don't know why its that fast but it is.

>> No.7609971

>>7609918
By definition. Using the definition of a meter defined to be some bullshit from the Eiffel tower to somewhere being a kilometer or something, we observe a number close to 299792458. We redefined the meter so that c=299792458 m/s.

Or you can just better units and set c=hbar=1, either way is up to you.

>> No.7610564

>>7607125
So is the question about gravity basically whether or not there is a field/gauge boson or if gravity is simply a warping of spacetime (in which chase there is no field/boson for gravity)?

>> No.7610577

>>7609669
The number means jack shit, fool.

If you put it in km it's

299,792 kilometers per second

OMG that number must be magic too.

C is C. How we define it is arbitrary.

>> No.7610586

>>7609685
The number itself is completely insignificant - it's just a matter of unit choice. It could just as easily be expressed as "1" , 1 lightsecond/second.

The reason it is important is what it means. It's not just a speed - it's a UNIT CONVERSION.

Space and time are both just dimensions. We can measure intervals in space dimensions with rulers, and intervals in time with clocks. But these are all just units of interval, like inches vs feet.

c is the conversion factor between space units and time units. If you could measure the time dimension with a ruler, an interval of one second would be 300,000-ish meters long. The number itself is as unimportant as saying 12 inches equals 1 foot.

>> No.7610605

>>7607125
>spacetime
is a descriptive model
like geometry, it claims no physical (causal) existence

>> No.7610786

>>7607125
Gravity is just another point of view for the same phenomenon. A particle which experiences no external force follows the geodesic equation in a curved space. A geodesic can be thought of as a straight line but in curved space. That's all. If we now go to a coordinate frame, which is not curved, the trajectory does not look like a "straight line" anymore but looks accelerated. In the Newton point of view, this can be considered as a force, which we call gravity.

If you now add the Einstein field equations, which tell you how space is warped by energy, you have General Relativity ;)

>> No.7610954

>>7609685
>our understanding
The point of it is that every understanding is from its own frame of refernce. "The universe" doesn't exist without an observer.

>> No.7610968

>>7607166
Picture two longitude lines on a globe. Here north represents future.

>> No.7611127

>>7607125
Gravity according to GR. Is the effect we notice by the warping of the spacetime fabric.

By warping, it constitutes that a straight line in 3d-spacetime, will be a curved path. So the body is not effected by any force, simply following the straight path that is through spacetime. But that line is bent so it will fall into whatever the curve bends into.

In this case, mass, bends the spacetime fabric. And objects with mass will eventually fall into eachothers gravity-well.

>> No.7611133

>>7609522
No. They are one and the same. There is no timr without space. And no soace without time.

>> No.7611199

>>7607125
Matter follows inertial paths through spacetime.
Mass curves the paths.

We interpret this change of inertial paths as a gravitational force.