Before we talk about gravity, let's talk about
a case where you can build a "box" to screen a
I bet you know that there is such a thing as
electrical charge - some things are
positively charged and some are negatively
charged, and opposite charges attract while
like-charges repel. It turns out you can build a
"box" that screens electric charge, called a
Faraday cage. A good example of this is in
your microwave which is basically surrounded by a
metal box that screens the effect of charge.
Why you need this is that charges are used to
cook your food in a microwave and you don't
want them cooking anything outside of your
microwave. But the reason it works is that there
are two kinds of charge. Negative charges attract
other positive charges near them so that, far
away, you don't see the negative charge but the
combination of the negative charge and the
positive surrounding charge.
It turns out that far enough away, these two
cancel each other out and you don't detect any
charge. Metal has a lot of easily movable charges
in it, so metal boxes are a good way to screen
charge. The details are a little more
complicated than what I just said, but I think the
basic idea is the same.
Now, it turns out that gravity only has one
kind of "charge" because all matter attracts.
So, as of right now, there is no known way to
build anything to screen gravity. There are good
(but complicated) reasons to think that we will
not discover matter that repels other matter, but
I don't know for sure if it is definitely
impossible. So my guess is that you can't
build a box to screen gravity. I hope that
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