/sci/ - Science & Math

[Anonymous No.6886244]

I've been trying to wrap my head around general relativity and I still don't understand what Einstein was trying to do. Why did Einstein think Newton's model was fundamentally broken? Eliminating the concept of gravitational force just seems bizarre especially since gravitational acceleration isn't even constant. There's obviously a force there.

[Anonymous No.6886250]

What Einstein was more/less trying to say was that gravity isn't its own force, it's a warping of spacetime.

Some semi recent studies in gravity shielding, however, suggest that gravity is a form of radiation/wave energy, with its own frequency. Also, gravity takes time to travel (the speed of light, actually).

Relativity and the warping effects on spacetime still hold true, but they may be an effect instead of a cause.

[Anonymous No.6886282]

Newton's model isn't "broken", not surprisingly we still use it daily for many applications.

What happens is that it's incomplete, however given certain conditions (such as a stationary weak field produced by nonrelativistic matter) you get

<span class="math">\nabla^2 \phi = 4\pi G \rho [/spoiler]

Where G is the gravitational constant, rho is the density of the mass and phi the Newtonian potential, and since the mass is nonrelativistic we can further claim

<span class="math">T_{00} \simeq \rho [/spoiler]

That, is the energy density is approximately the mass density, both equations yielding

<span class="math">\nabla^2 g_{00} = -8 \pi T_{00} [/spoiler]

Where we also used that the metric tensor is related to the Newtonian potential by

<span class="math">g_{00} = -(1+2\phi) [/spoiler]

So as you can see for a weak nonrelativistic field we get

<span class="math">G_{ab} = -8 \pi T_{ab} [/spoiler]

[Anonymous No.6886301]

I'm sick of people saying Newton wasn't wrong. The whole point of the name relativity is that it contrasts with Newton's idea of there being an absolute point of reference.(space)

[Anonymous No.6886350]

>>6886301
you can assume the universe behaves like newton assumed it did for most everyday purposes
even nasa uses "wrong" newton math for its space launches
give the old coot some credit, he came up with this shit some 400 years ago

[Anonymous No.6886352]

>>6886244
The funny part is Einsteins model is fundamentally broken as well, even though it works so well in practice

[Anonymous No.6886356]

>>6886352
How is it broken if it works?

[Anonymous No.6886360]

If mass deforms spacetime why do the outer edges of a galaxy rotate at the same speed as the core?

inb4 hurrdurr dark magic

[Anonymous No.6886362]

>>6886356
In the same way that Newton's ideas were fundamentally broken even though they work.

[Anonymous No.6886383]

>>6886360
they don't
they just rotate a lil bit faster than they should

[Anonymous No.6886387]

>>6886360
>inb4 hurrdurr dark magic
Damn. I can't inb4 retard.

[Anonymous No.6886390]

>>6886360
>If I can't see it, it doesn't exist!

[Anonymous No.6886398]

If your mom has a particle with electrical charge <span class="math">q[/spoiler] resting at position <span class="math">r_M[/spoiler], say 5000 miles from you, then it's electrical field goes as <span class="math">\propto\frac{1}{|r-r_M|^2}[/spoiler].

Now if your mom accelerates the charge further away from you, i.e. <span class="math">r_q(t)[/spoiler] changes its value with time, then, from your perspective, it has a velocity <span class="math">v_q:=r_q'(t)\neq 0[/spoiler], and so there is a current <span class="math">j=q·v_q[/spoiler].

The fact that she moves the charge isn't instantaneously clear to you though: the light of that event first has to travel to youfor you to see it, and also the field doesn't change instantaneously. In particular, what happens is that the Maxwell equations
<span class="math">(d/dx)B\sim j+(d/dt)E[/spoiler]
go "oh shit, there is a moving charge/current! It's time to radiate and change the electrical field."
The electromagnetic wave propagates everywhere and soon your <span class="math">\propto\frac{1}{|r-r_M|^2}[/spoiler] will be corrected accordingly. If your mom moves away, the field will go down.

Now gravity also goes like <span class="math">\propto\frac{1}{|r-r_M|^2}[/spoiler], but there were no Maxwell equations of gravity.
Here, if your mom throws a book through the room, and it's position <span class="math">r_B(t)[/spoiler] changes, then the force follows it as <span class="math">\propto\frac{1}{|r-r_B(t)|^2}[/spoiler]. There are no sophisticated gravitational waves. Once the book movies, it gravitational force on you chances in that same moment.
The above doesn't matter for Newton and his absolute space.

But Einstein had special relativity in 1905, and it said (muh Interstellar twin paradox etc.) that if someone moves, his axis of "now" tilts. Everybody has its own "now".
In particular, if someone moves a book away from you AND by moving stuff is able to affect things in his new frame instantaneously, then he would actually affect not you but your past you.
See http://en.wikipedia.org/wiki/Tachyonic_antitelephone

To answer your question, Einstein wanted a more dynamical gravity.

[Anonymous No.6886408]

>>6886301
for nonrelativistic weak fields the metric tensor is pretty much the gravitational potential

see >>6886282

>>6886362
what do you mean by 'broken'? every experiment that has been conducted up to date since the publishing of general relativity by Einstein in 1916 has concurred to its validity

see

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

[Anonymous No.6886410]

>>6886398
>was expecting a clever yo momma joke
>anticlimactic
>7/10 but only because of qt1.14

[Anonymous No.6886415]

Newton's model failed to explain why the speed of light was a constant no matter the referential. Scientists knew by 1890 that Classical Mechanics was not complete thanks to the experiments conducted by Michelson and Morley.

So Einstein theorized special relativity, and then general relativity, which are based around that and can still give Newton's equations given specific conditions.

[Anonymous No.6886417]

>>6886244
Read the first few pages of this: http://www.academia.edu/3518605/Deriving_Einsteins_Field_Equations_of_General_Relativity

>Einstein’s rumminations on light while forming his theory of Special Relativityled him to find a dire contradiction in Newton’s theory of gravity. Einstein discovered that nothing can travel faster than the speed of light; the speed of light is essentially auniversal speed limit. However, Newton’s gravity equation has no time-dependence. The gravitational force of one mass on another acts instantaneously. Say, for instance, if the sun in our solar system were to, hypothetically, vanish, Newton’stime-independent version of gravity says that the planets would immediately spinout of orbit. This, however, cannot be true Einstein thought because if nothing cantravel faster than the speed of light, how can a gravitational affect travel faster than the speed of light? To solve this issue, Einstein developed the General Theory of Relativity, where gravity was not instantaneous, but its effects traveled at the speed of light.

[Anonymous No.6886419]

>>6886410

He wanted more dynamical gravital because yo momma so fat tho

[Anonymous No.6886420]

>>6886410
I started our writing r_q and changed it to r_M, which is standard for moving mass, and implied it stands for mamma.

>>6886398
I could add that special relativity was found exactly because their laws, in turn, "do not agree" with Newton, in the sense that they transform weirdly in a Newtonian spacetime. The Maxwell equations were found by thinking on how electric and magnetic phenomena work together and Lorentz/Einstiens spacetime (which has the time dilation shizzle) is the one in which the Maxwell equations fit into.
Einsteins famous paper was "On the Electrodynamics of Moving Bodies", after all.

Electromagnetism was taken seriously, Newton spacetime was corrected accordingly to Minkswski spacetime, which then didn't fit with Newton gravity anymore, so they broke down spacetime again, literally bending it so gravity could live in it, using Riemann geometry and the Italians math.

Btw. you can work out to what extend Einsteins equation mirror electrogmagnetism, see
http://en.wikipedia.org/wiki/Gravitoelectromagnetism

[Anonymous No.6886431]

>>6886410
I started our writing r_q and changed it to r_M, which is standard for moving mass, and implied it stands for mamma.

>>6886398
I could add that special relativity was found exactly because Maxwells laws "do not agree" with Newton, in the sense that they transform weirdly in a Newtonian spacetime. Einsteins famous paper was "On the Electrodynamics of Moving Bodies", after all.
The Maxwell equations were found by thinking on how electric and magnetic phenomena work together and Lorentz/Einstiens spacetime (which has the time dilation shizzle) is the one in which the Maxwell equations fit into.
Btw. you can work out to what extend Einsteins equation mirror electrogmagnetism, see
http://en.wikipedia.org/wiki/Gravitoelectromagnetism

Electromagnetism was taken seriously, Newton spacetime was corrected accordingly to Minkswski spacetime, which then didn't fit with Newton gravity anymore, so they broke down spacetime again, literally bending it so gravity could live in it, using Riemann geometry and the Italians math.

[Anonymous No.6886445]

Einstein took work from earlier scientists.
Thought about it, changed it and revamped bunch of times.
Finally got a working framework.
Which he couldn't prove correct.
Till others did,for him.
He stands on the shoulders of many.

[Anonymous No.6886547]

>>6886417
>:http://www.academia.edu/3518605/Deriving_Einsteins_Field_Equations_of_General_Relativity

That thesis is so unoriginal.

[Anonymous No.6886564]

>>6886415
>not complete

that's the keyword here. newtonian mechanics and gravity aren't wrong, just that: incomplete. we use them daily without a problem (i propose a challenge here, drop a coin from a building and the time it takes to fall can be computed through newtonian mechanics, hell i can even find out what earth's gravitational acceleration is like that). surely it has a limit because it's not the whole "picture" but rather an approximation that works for slow speeds

[Anonymous No.6886568]

>>6886244
http://io9.com/the-200-year-old-mystery-of-mercurys-orbit-solved-1458642219

[Anonymous No.6886895]

>>6886282
>Newton's model isn't "broken", not surprisingly we still use it daily for many applications.
>many applications

Isn't Newton's model used for almost all applications (as compared to relativity) in the modern world?

What applications is general relativity specifically used for that could not be achieved without it? I'm not trolling, I have no science background, but am curious about this.

[Anonymous No.6886909]

>>6886895
GPS is the first thing that comes to mind

[Anonymous No.6886950]

>>6886244
because as a scientist he had to know that all theory have a missing link.
everything in science can be proven otherwise, but on most topics we just doný know how yet.
therefor sciense is pretty stupid in a way, but it help to shut up uneducated people because someone with a lot of knowledge can talk and reason better that the uneducated who then just gives up, hence he or she will be in your control to do the job you are asking him or she to do.

[Anonymous No.6886957]

The amount of retarded shit being spewed in this thread is off the charts

[Anonymous No.6886982]

>>6886895
Predicting the orbit of Mercury.

[Anonymous No.6887522]

Newton's model had no mechanism and the formula cannot fully describe the behavior of gravity.

Einstein approached the problem by asking himself what happens when a body is at rest. You may think you are at rest right now, but if you feel the force of gravity then you might actually be accelerated, since without a known frame of reference you may be in a gravitational field or you may be accelerating in a rocket.

Einstein discovered that an object truly at rest feels no forces at all. There are only two times a body feels like this, one, infinitely far from all gravity, or two, in free fall. Einstein realized that a falling body is actually at rest, so therefore something else must be curved around it to be making it move: Spacetime.

[Anonymous No.6887594]

>newton
>posts a picture of Leibniz

ebin troll

[Anonymous No.6887664]

>>6886445
>This is what /pol/ actually believes

[Anonymous No.6887699]

>>6887664
No, /pol/ believes that Einstein is Jewish and thus contributed absolutely nothing to anything because only white people from a very specific region of Europe are able to think.

[Anonymous No.6887713]

>>6887522
>Einstein discovered that an object truly at rest feels no forces at all.

But isn't a tidal "force" a force? That's why the equivalence principle didn't make much sense to me. How can they be equivalent situations when they're most clearly not?

[Anonymous No.6887830]

>>6886445
So like every scientist ever ?