# Thread: would light emitted on earth orbit the earth?

1. ## would light emitted on earth orbit the earth?

if there was a universe that only had a planet in it ( earth ) and you emitted some light because of the gravitational curvature of the earth would light eventually find an orbit ( I realize very far away ) around the earth?

So the earths gravitational influence would go on infinitely ...

For infinity the light would be under the influence of earths gravity.

Wouldnt that mean that at some distant point it would find its orbit?

2. ## Re: would emitted on earth orbit the earth?

I Think not. The Earth would have a gravitational curve in space but that curve would only deflect the light beam slightly at the outset. It would continue on essentially a straight path once it has past the major curve. The influence past that as far as curvature would be negligible and since photons do not have mass, there would be no other influence on the photons.
I suspect light would continue on in that direction for infinity.
The stuff you ask... Even as I was typing this, my mind kept wanting to bend back to saying "Yeah, but if we are talking an infinite univserse and infinite time, wouldn't it eventually wend its way back?" Had to keep reminding myself, photons have no mass.

3. ## Re: would emitted on earth orbit the earth?

Originally Posted by Neverfly
I Think not. The Earth would have a gravitational curve in space but that curve would only deflect the light beam slightly at the outset. It would continue on essentially a straight path once it has past the major curve. The influence past that as far as curvature would be negligible and since photons do not have mass, there would be no other influence on the photons.
I suspect light would continue on in that direction for infinity.
The stuff you ask... Even as I was typing this, my mind kept wanting to bend back to saying "Yeah, but if we are talking an infinite univserse and infinite time, wouldn't it eventually wend its way back?" Had to keep reminding myself, photons have no mass.
but the earth has infinite curvature on an infinite universe. so even though it is very slight its curvature on the topology of space-time is still there ... I think this would be similar to the ant and the rope ... every light year would result in SOME curvature. If some curvature is there then eventually it would orbit ... right?

4. ## Re: would emitted on earth orbit the earth?

Originally Posted by tom
but the earth has infinite curvature on an infinite universe. so even though it is very slight its curvature on the topology of space-time is still there ... I think this would be similar to the ant and the rope ... every light year would result in SOME curvature. If some curvature is there then eventually it would orbit ... right?
No, orbital velocity *decreases* with distance. So, if light doesn't orbit at a close distance, it's not going to orbit at a farther distance.

For something the mass of the earth, the radius would have to be tiny for light to orbit--it'd be a small black hole. The Planck radius of the earth is ...

5. ## Re: would emitted on earth orbit the earth?

Grapes, good to see ya posting. Did you take a break?

6. ## Re: would emitted on earth orbit the earth?

Originally Posted by grapes
The Planck radius of the earth is ...

If you had a mass the size of the earth, and it was concentrated into a mini-blackhole, the Schwarzschild radius would be 9mm, that's the radius where the escape velocity is the speed of light.

7. ## Re: would emitted on earth orbit the earth?

Originally Posted by Neverfly
Grapes, good to see ya posting. Did you take a break?
I lurk some

8. ## Re: would emitted on earth orbit the earth?

Originally Posted by grapes
No, orbital velocity *decreases* with distance. So, if light doesn't orbit at a close distance, it's not going to orbit at a farther distance.

For something the mass of the earth, the radius would have to be tiny for light to orbit--it'd be a small black hole. The Planck radius of the earth is ...
Even when taking Ant and rope into acct?

9. ## Re: would emitted on earth orbit the earth?

Originally Posted by tom
Even when taking Ant and rope into acct?
Not remembering ant and rope, explain please.

But in a nutshell, orbital velocity decreases as you move away from a central mass. It's not going to *increase* up to the speed of light.

10. ## Re: would emitted on earth orbit the earth?

Originally Posted by grapes

If you had a mass the size of the earth, and it was concentrated into a mini-blackhole, the Schwarzschild radius would be 9mm, that's the radius where the escape velocity is the speed of light.
the photon sphere would be around 18mm....something like that..

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