# Why does spacetime warp around mass if it doesn't have mass?

Tags:
1. Jul 27, 2014

### Natsirt

Whatever spacetime be made of strings or some other erotic substance it seems that it doesn't have mass so what causes it to warp around mass, shouldn't it pass right through?

2. Jul 27, 2014

### Mr-R

And who said it has to be some kind of matter to have mass? references?

Strings? hmmm

3. Jul 27, 2014

### Staff: Mentor

I like it more this way, but your auto-correction software may have messed up what you're trying to say.....

4. Jul 27, 2014

### Natsirt

I guess a more precise question would be why does mass effect mass even if it can sometimes pass through things like neutrinos do or maybe how the strings in String theory might?

5. Jul 27, 2014

### Mr-R

The bigger Mass warps spacetime and the other smaller mass will follow the geodesic. Neutrinos pass through matter because they don't feel the strong force and also don't have charge. (electromagnetic). But even Neutrinos cause spacetime curvature because they some mass ,therefore they "affect mass". But the effect can't be observed because it is very small.

6. Jul 27, 2014

### Natsirt

So why doesn't spacetime go through matter unaffected?

7. Jul 27, 2014

### Mr-R

Why should it? it is not matter.
It is space, certainly not matter, and time, which is definitely not matter. Space-time.

You should ask how matter affects space-time. Read up the Energy-momentum tensor. I will leave it to the rest of the members because I don't think I can answer that.

8. Jul 27, 2014

### Master Sashin

Spacetime is like a forcefield that takes up volume, therefore if you bring a mass into it, the spacetime cant escape the universe so it is forced to curve arroundd the mass and apply a force to it

9. Jul 27, 2014

### Natsirt

That makes sense, thankyou

10. Jul 27, 2014

### Master Sashin

Im only in grade 10 so i have little knowledge so maybe research a bit and tell me if im right

11. Jul 27, 2014

### Natsirt

I'm in 10th too. Space-time does act like a force field, I knew that but I needed to hear it in the way you said it. Some of what we have been discussing is string theory and how the energy that makes the strings vibrate means they won't pass through things, instead they'll act as a force or a "force field" so your not wrong.

12. Jul 27, 2014

Staff Emeritus
Natsirt,

You seem to be trying to understand by physics by putting the words together in the right order. This, I am afraid, will not get you to where you want to be. Physics is inherently mathematical. People can give you verbal explanations, but they are at best approximate, and you will not be able to combine them and get something that is correct. Or even sometimes make sense.

PS Erotic materials are something other than what you wrote.

13. Jul 27, 2014

### ChrisVer

In general I don't see why someone would try to imagine these things with strings and make his/her mind more confused over it. Especially when he/she doesn't have the appropriate basic knowledge on the field apart from maybe some scifi books.
We know that mass and energy are able to act as sources of gravity, because of the Einstein Equations of General Relativity. From the one side of your equations, you have the Einstein tensor which contains the information of your spacetime geometry. On the other side, you have the energy-momentum tensor which comes straightforward from the existence of matter and/or radiation. It's due to this that you actually have that mass,energy can interact with spacetime curvature (so spacetime is not unaffected from matter). Why do you get this result? The Einstein equations don't need the strings to be extracted. You extract them from minimizing what we call the "Action" in classical mechanics. Strings only come into play as a candidate to quantize gravity.
To quantify this for you, imagine that you have $A=B$... A corresponds to the geometrical features of the spacetime, and B to the matter and radiation content you consider. If you change B, A will have to change too so you keep the equality. Of course the relation is different:
$G_{\mu \nu}= 8 \pi G T_{\mu \nu}$
with $G_{\mu \nu}$ the Einstein tensor, $T_{\mu \nu}$ the energy momentum tensor and $G$ the newton's gravitation constant.
When you want to talk about neutrinos passing through matter, well that needs extra knowledge on the physics of particle physics. Indeed the neutrinos can pass through matter, but that doesn't mean that a huge (super-huge) amount of neutrinos couldn't possibly cause some change in your spacetime curvature. However, when one talks about neutrinos interactions, he doesn't have in mind gravity- because their gravitiational interactions are very small in power compared to weak interactions they are subject to (to an order of $10^{-25}$ at "normal" energies- http://en.wikipedia.org/wiki/Fundamental_interaction). The weak interactions however are so rare, that neutrinos indeed pass through matter unaffected. Or another way to state it, is by saying that the probability for a neutrino to interact is actually so small that in general, most of them, can pass through whole planets unaffected. Because of that, just seeing particles as small balls of some mass colliding with other balls, is actually a wrong idea - maybe this works only as a limit approximation and only "effectively".
On the other hand, as photons, so neutrinos can be subject to spacetime geometry, and so they follow the paths they do- for example their trajectories can be bend from a gravitational source (like a heavy planet, star or so on).

Last edited: Jul 27, 2014
14. Jul 27, 2014

### Staff: Mentor

I most strongly recommend that you learn Newtonian physics before trying to learn general relativity! It is like trying to do gymnastics before learning to crawl.