Thread: Laymans' question about gravity...

Hiya,
Are the effects of gravity felt instantaneously regardless of distance?
If (lets say) Venus were to suddenly disappear, would this begin to immediately affect the orbit of the asteroids or would there be a delay (nothing travels faster than light)?

Without doing any research, I suspect the answer is unknown, since there is no proven mechanism for gravity.

You are absolutely correct, nothing travels faster than light.

According to Einsteins theory of general relativity (I think it was general and not special relativity.) But, either way, he stated that gravity waves travel just as fast as light. So if Venus suddenly disappeared there would be a delay. However, there would also be a delay before we would even know that it had disappeared, so until the light reaches us to tell us it is gone we will still feel the gravity. Both should happen at the same time, we will notice it's gone and also lose the gravitational pull.

Guess I'll just have to blow up Venus to find out..lol.
btw - is "reward of the atheist" a reference to Schrodingers cat?

Ok, I see that makes sense, I didnt know that gravity and light move at the same speed (actually I didnt know that gravity moves at all). I don't know much about this kind of thing but its fascinating just the same..

Ok, I wasn't sure of your level of understanding on the subject.
To help you understand the concepts behind it check out this video:
http://www.youtube.com/watch?v=0rocNtnD-yI
I didn't watch all of it cause it's kind of long but hopefully it will clear it up. BTW: I just searched in youtube for general relativity so maybe you can find other videos too, or try searching for gravity waves.

Originally Posted by Maldwyn

Guess I'll just have to blow up Venus to find out..lol.
btw - is "reward of the atheist" a reference to Schrodingers cat?

Nah. It's about how atheists believe there is nothing after life.

So he's sat in an empty room

Nah. It's about how atheists believe there is nothing after life.

So he's sat in an empty room

So did Schrodingers cat. Then someone opened the box... :-D

Think about a simple radio transmission. To send a radio signal a modulated current is sent through the transmitting antenna, thereby constantly changing the electrical field that the electrons inside of it produce - and with every varying electrical field there is an associated magnetic field. The receiving antenna doesn't pick up the change in the electromagnetic field immediately because that change propagates through space at a certain speed. That propagation is of course what we describe as "electromagnetic waves" and EM waves travel at the speed of light (in a vacuum).

Same goes for gravity. If you could somehow modulate the mass of an object and then had some way of measuring those changes at the receiving end you could achieve communication through "gravity waves". Of course this is much harder (if at all possible) than with electromagnetism. Plus gravity is a much, much weaker force that the electromagnetic force and thus the effective range would be much smaller.

So in short, like previous poster wrote, the effects of gravity travel at the speed of light. This was pointed out in "A Brief History of Time" where Hawking relates that if the sun suddenly vanished the Earth would still be following its orbit around the non-existent sun for seven minutes - the time it takes for sunlight to reach the Earth.

Originally Posted by Maldwyn

Guess I'll just have to blow up Venus to find out.

Wouldn't work. The mass of Venus would still be there and it would still have the same centre of gravity. (At least for the first couple of years)

please explain how the gravity of Venus remains if it is gone.

Originally Posted by fizzlooney

please explain how the gravity of Venus remains if it is gone.

If you would blow up Venus, the mass doesn't disappear. It would become a cloud of debris with exactly the same mass, but a lower density, as Venus. Over time, Venus might reform, the debris might smear out over it's course around the sun, or it would dissipate into space, depending on the strength of the explosion.

As long as the cloud of debris is sufficiently small on the scale of the solar system, it has the same effect as the planet. Much like the centre of gravity of firework rocket keeps following a parabola after explosion, the centre of gravity of the cloud of debris will keep following Venus's path around the sun.

My apologises for our young Maldwyn here,

Hopefully a method more pleasing for you Bender is if we just got a load of intergalactic transporter ships to carry Venus off to a more suitable place far enough away so that the gravitational pull is not a factor in our experiment!

I'll just get fedex on the line quick!

LoL sorry couldnt resist!!!

Darn. And I was THIS close to pushing the "Blow up Venus now" button.. lol

:P
I've got the annoying habit of answering jokes with a serious response.

btw: having DHL transport Venus away also wouldn't get the sudden disappearance you're looking for. It would only very gradually move away

Originally Posted by Street_Physicist

You are absolutely correct, nothing travels faster than light.

Phase velocity?

Originally Posted by Bender

btw: having DHL transport Venus away also wouldn't get the sudden disappearance you're looking for. It would only very gradually move away

Gradually move away from us after a delay of 2.2 minutes from DHL's departure with venus.

Originally Posted by harvestein

Originally Posted by Bender

btw: having DHL transport Venus away also wouldn't get the sudden disappearance you're looking for. It would only very gradually move away

Gradually move away from us after a delay of 2.2 minutes from DHL's departure with venus.

Which isn't all too different from it's movement around the sun only being felt on earth after a delay. 8)

Originally Posted by sox

Originally Posted by Street_Physicist

You are absolutely correct, nothing travels faster than light.

Phase velocity?

Here is a good demonstration of why that doesn't count. It's really just an illusion.