# Newton's law of gravity or Einstein's general theory of relativity?

1. Nov 4, 2013

### Remon

I don't know much about the two ideas but I'm confused because the two theories seem to contradict each other, if all matter (with mass) bends space, then there is no such thing as "gravity", or maybe gravity is just the actual bending of space, so should we refute the idea of "gravity"? or just alter its meaning to be "the bending of space due to the presence of some amount of mass"?

2. Nov 4, 2013

### arildno

As long as you see Newton's law as THE valid approximation of Einstein's theory for "everyday" occurences, there is no contradiction.

3. Nov 4, 2013

### Remon

So you're saying that we ("we" being the general public, not scientists or physicists, etc.) should just believe the somewhat "inferior" theory (gravity) simply because it's easier and easily applies to "everyday" actions? Because I would have it if we were all informed of both ideas since the way I see it is high school and university (so far) have always talked about gravity & mass but never once mentioned relativity, which just angers me

4. Nov 4, 2013

### Staff: Mentor

I think Relativity should be taught in high school physics too, but for everyday use for motion or gravity calcs, it is basically never needed. GPS is so ubiquitous now though it would be nice if people knew how it applied there.

Last edited: Nov 4, 2013
5. Nov 4, 2013

### Remon

But it still applies to every object with mass, even apples and oranges bend space to a certain degree, so not only does it apply to everyday objects but its also just as easy to understand as gravity, I hate being taught the wrong ideas or not even taught the correct ones at all.
School taught me that every object on earth has a certain (yet very tiny) gravitational influence on other objects, but that's only part of the story, why couldn't they just simply tell us that "space bends around mass"? its very simple and applies to everyday objects...broken education system I suppose.
I know I'm ranting about schools but it just makes me angry that all my knowledge about relativity comes from outside of school

6. Nov 4, 2013

### phinds

I think you are overly optimistic in thinking that the general public will understand "mass bends space" as easily as they can accept "objects attract each other".

Also, no more than a tiny fraction of the populace will EVER have any actual use for GR but a far greater number will have need of Newton.

7. Nov 4, 2013

### Office_Shredder

Staff Emeritus
To such a small degree that before relativity was discovered nobody could find a contradiction in Newton's theory.

Neither of these statements is true. To everyday objects relativity's effect will be smaller than the number of significant digits, and general relativity is way harder to understand on a computational level than gravity is.

General relativity is also wrong (experimentally contradicted on a quantum level), so how do you feel about that?

8. Nov 4, 2013

### Remon

I think I classify as "general public" and I think I mostly understand the concept of relativity, so why not everyone else? I taught it myself and I'm not even 19 yet (I'm not even smart too) so I don't see how everyone else would have difficulty understanding at least just the main idea (not the methods behind it) especially when someone else teaches them the idea (rather than being self-taught), not to mention that many other ideas that are being taught at other subjects are actually harder to understand than the simple "bending of space"

9. Nov 4, 2013

### arildno

Since you show such extreme contempt for me, by not bothering to relate to WHAT I wrote, but just invented a strawman argument, I see no reason to discuss with you before you cite my properly (rather than your despicable "so you are saying"-falsifacition), AND give an unconditional apology for your disrespectful behaviour.

10. Nov 4, 2013

### Remon

Then how come it's still accepted today?

11. Nov 4, 2013

### Staff: Mentor

12. Nov 4, 2013

### Remon

Relax, I think it was just a simple misunderstanding. I thought you meant that we should all just "trust" more in gravity (and ignore relativity to a degree) due to the convenience of it being applied to "everyday occurrences", I guess I misunderstood you? Don't get so defensive, the last thing I want to do is start an immature argument over the internet based on a simple misunderstanding, I didn't mean to offend you or anyone else.

13. Nov 4, 2013

### arildno

Well, stop thinking, since you don't have the mental discipline to do that yet.
Start quoting people directly instead, rather than making your own fantasybased versions of it.
THEN, in direct reference to the words in those quotes, you may start to build up sufficient mental discipline.

14. Nov 4, 2013

### phinds

You would likely find it informative, and apparently surprising, if you were to pick the next 10 people coming down the hall in your school and see how they do at understanding the two concepts.

15. Nov 4, 2013

### WannabeNewton

There is a general misconception (for acceptable reasons) that the concept of gravity as a manifestation of curved space-time and space-time geometry is unique to general relativity (GR). There are entire classes of gravitational theories which can be cast this way, including Newtonian gravity. The differences between Newtonian gravity and GR go beyond the interpretation of gravity as a manifestation of space-time geometry vs. as a force.

Indeed roughly speaking the differences between these two gravitational theories are codified in the differences between their field equations, in particular in that Newtonian gravity is a scalar theory of gravity whereas GR is a tensor theory of gravity, and that GR is a relativistic field theory whereas Newtonian gravity is not. These differences dissolve when we go to the Newtonian limit wherein the experimental predictions of the two theories are, to sufficient order in $1/c^2$ (usually first order), exactly the same (if we don't ignore higher order terms in $1/c^2$ then effects like frame-dragging will arise).

In other words, there is absolutely no contradiction between the two in terms of interpretation; the differences are manifest in the differences in experimental predictions (which derive from the differences in the field equations) and foundations of the respective theories (i.e. relativistic vs non-relativistic) when one is not in the Newtonian regime.

16. Nov 4, 2013

### Remon

Since it seems that all you want to do is try to insult me in an "intelligent" way just for a simple misunderstanding, I'm just going to stop replying back to you.

Last edited: Nov 4, 2013
17. Nov 4, 2013

### arildno

Fine.
Tip:
Start reading people's posts, rather than making travesties out of them. You are not yet there

18. Nov 4, 2013

### Remon

Are you saying that a lot of people actually understand the two concepts but most of them just keep it to themselves? Because I thought of that before since I obviously can't be "one of the few", but I don't see many people mentioning relativity in everyday conversations lol

19. Nov 4, 2013

### WannabeNewton

Based off of your posts, it is clear that you don't understand relativity in the least and that you have an even bigger misconception about higher theories that extend classical mechanics in general. I don't see what age has to do with this.

20. Nov 4, 2013

### Staff: Mentor

Have you ever attempted to perform a calculation using General Relativity?

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