# How does matter bend space?

I am 9 years old. Can anyone explain this to me?

## Answers and Replies

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mathman
Science Advisor
I am 9 years old. Can anyone explain this to me?
Not likely. It is part of the theory of general relativity, which is taught no earlier than junior lever physics in college.

Drakkith
Staff Emeritus
Science Advisor
It might be tough since you are 9 years old, but I'll give it a shot.

Matter, which is what everything we see and touch is made of, has something called Mass. Mass is what causes objects to have weight and to resist being pushed and pulled. The more massive something is the harder it is to push it and pull it and the more it weighs. (When used this way, "massive" means it has more mass, not that it's size is really big. Although more massive objects typically have larger sizes, hence why massive is usually referred to as being very big.)

This "mass" is simply a term that describes those effects. It turns out, that the more mass something has, the more gravity it has, which is why the Earth pulls you down with such force while you cannot feel any force from your computer monitor, it isn't massive enough!

About 100 years ago, a guy named Albert Einstein proposed that gravity isn't really a force like a magnet has with another magnet, but is instead a property of space and time. In his theory, known as General Relativity, he proposed that space and time are united into "spacetime" and that it is bent or curved by mass. When an object moves through this curved spacetime it turns out that the shortest distance between two points is no longer a straight line in space, but is a curved line, which makes us get closer to another object. So the more mass something has the more spacetime around it is curved, meaning there is stronger gravity.

I recommend picking up the following book. It's very interesting and easy to read. (And has pictures!)
https://www.amazon.com/dp/1848310579/?tag=pfamazon01-20&tag=pfamazon01-20

Thank you - I understood that well. Thank you for suggesting the book - I'm going to save up for it!!!!!!!!!!!!!!! :)

Drakkith
Staff Emeritus
Science Advisor
Thank you - I understood that well. Thank you for suggesting the book - I'm going to save up for it!!!!!!!!!!!!!!! :)
Well, I said it was easy to read, but that was for me, and I'm 27. So no promises lol. Out of all the books on science I've read, that one was one of the most enjoyable because it is very different from the others. It's almost like a comic book in that every page has pictures and stuff on it to help you understand. You may be able to look a few pages on amazon.

ill use the classic bed example. mass bends space

imagine space being a bed mattress. put something with a lot of mass on it, a bowling ball, and put something with less mass on the other side, a golf ball. think of the bed being space and you just bent it :)

put the golf ball close enough and it will crash into the bowling ball. thats gravity! hope that helps

Hi quantum:
While nobody understands yet exactly WHY gravity is so different from other stuff [forces] we observe, it turns out it seems really, really different based on what we know so far.

A nice picture of what we think is going on can be found here:
http://en.wikipedia.org/wiki/Introd...#Curvilinear_coordinates_and_curved_spacetime

Like the prior post discussing the curvature in a mattress, or a rubber sheet, we really can't represent [picture] the curvature of time, but the blue curved lines in the Wikipedia picture do give an idea of how space is curved and might cause the satellite in the picture to rotate around the earth. The satellite tends to follow the curves shown.

The text under the picture refers to the curvature seen in the blue lines as 'warping' which a common term used to mean 'curving', but the text is not correct to say the blue lines represent the curvature of space AND time....they really are just some 'warping' or curvature of space...like a mattress or rubber sheet with a weight in them.

An example of the 'warping' of time would be that near the strong gravitational influence of earth [where the blue lines sink 'down'] in the picture, space is more curved and time is slower than far away, say on the orbiting satellite.

So 'warping' of both time and space [spacetime] IS gravity!!
But nobody knows 'why' except that is what we observe!!

It does so by making things move as if the space around them is bent and there is no other way to go. The term "bending space" is just a way of describing that effect. As the above post states, we dont fully understand how it does it. All we know is that the more dense the matter the stronger the space-bending effect becomes.

All we know is that the more dense the matter the stronger the space-bending effect becomes.
Could you explain why you think that the strength of space-bending depends on the density of matter?

Could you explain why you think that the strength of space-bending depends on the density of matter?

Because that's what observation indicates. In fact, our whole space exploration effort depends on the reliabiliy of this generally-agreed-upon conclusion. In fact, whole cosmological theories are built upon that observation.

Why do heavy objects bend space and what is it they are bending?http://www.askamathematician.com/20...s-bend-space-and-what-is-it-they-are-bending/

BTW

Please note that I did not say I believe that space is literally being bent. I said that objects react to gravity in a way as if space were being warped or bent in certain ways. That is a big difference.

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Because that's what observation indicates. In fact, our whole space exploration effort depends on the reliabiliy of this generally-agreed-upon conclusion. In fact, whole cosmological theories are built upon that observation.
I think you are mistaken.

I think observation dictates that curvature depends on the amount of mass not on the density of mass.

I think you are mistaken.

I think observation dictates that curvature depends on the amount of mass not on the density of mass.
Of course. That's what I meant but expressed it wrongly. I used the term density as a substitute for amount, which is wrong. Thanks for bringing it to my attention.