how can the presence of a gravitational field be detected?

Answer 1

Drop something. If it falls, there is a gravitational field. If you yourself are already falling but don't realize it, like the astronauts in orbit, you need to know your speed and direction to compute the gravity field.

Answer 2

I have a method of detecting gravitational fields that gives direction and quantification of the strength of the field in real time on x, y, an z axis. It does not require a void, lasers, or mirrors. First country to contact me with a serious offer will be able to purchase my method.

Answer 3

Do you mean 'detected' or 'measured'?
All mass has a gravitational field associated with it. That is a given.
If you are asking about measuring the field, there is the law of universal gravitation.

Answer 4

By utilizing a tool called the Gravitational Spectrum Analyzer.

Answer 5

Get an accurate clock. If it runs more slowly than a similar clock in intergalactic space, then you are in a gravitational field.

Answer 6

Gravitational lensing would be one way - the light from distant galaxies is "bent" by closer massive objects. We can see stars orbiting something invisible, from which we infer the presense of a black hole.

Answer 7

If you're free falling in it, you cannot detect it. This is Einstein's Equivalence Principle. If you are on a solid surface feeling weight, you have already detected it.

Answer 8

By observing an apple tree.

Answer 9

Throw a ball up and see whether it comes back to you.

Answer 10

Fall off what ever you are sitting on!