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### Author Topic: If light has no mass how can black holes capture it?  (Read 5920 times)

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##### If light has no mass how can black holes capture it?
« on: 12/09/2008 16:18:25 »

sir, as we know that the gravitational force could exist between two bodies having masses then how could blackholes (massed) capture (massless i.e gravity-less) photons (light rays)?

What do you think?
« Last Edit: 13/09/2008 11:54:08 by chris »

#### DoctorBeaver

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##### Re: If light has no mass how can black holes capture it?
« Reply #1 on: 12/09/2008 16:40:20 »
You have to be careful when saying that light has no mass. It is true that a photon has no rest mass, but photons are never at rest.

A thread appeared some time ago which elicited a comprehensive reply to this question. I'll try to find the thread and post a link to it here.

In the meantime, maybe someone else will interject with an answer.
« Last Edit: 12/09/2008 16:48:03 by DoctorBeaver »

#### Gabe2k2

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##### Re: If light has no mass how can black holes capture it?
« Reply #2 on: 12/09/2008 20:30:37 »
Although not well written I'm told in the thread " Is a Black Hole a point? " I attempt to help some of you understand a black hole. There is no actual proof that light, is in fact captured by black holes !

#### lightarrow

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##### Re: If light has no mass how can black holes capture it?
« Reply #3 on: 12/09/2008 21:09:39 »

sir, as we know that the gravitational force could exist between two bodies
having masses
then how could blackholes (massed) capture (massless i.e
gravity-less) photons (light rays)?

What do you think?
But the significant concept here is not the gravitational force but the gravitational field. If an object's mass where important, then why Galilei found that all masses have the same acceleration when they fall from Pisa's tower?

Take an object of 1 kg mass and release it in the void and it will move towards the Earth in a certain way.
Now take an object of 0.001 kg mass, then of 0.0000001 kg, ecc. Will you expect some difference in the trajectory and in velocity?
At the limit for m-->0 there will be any difference?

#### DoctorBeaver

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##### If light has no mass how can black holes capture it?
« Reply #4 on: 14/09/2008 12:08:12 »
Although not well written I'm told in the thread " Is a Black Hole a point? " I attempt to help some of you understand a black hole. There is no actual proof that light, is in fact captured by black holes !

There is no experimental proof, that's true. But every theory says that it is so.

#### lightarrow

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##### If light has no mass how can black holes capture it?
« Reply #5 on: 14/09/2008 12:33:21 »
Although not well written I'm told in the thread " Is a Black Hole a point? " I attempt to help some of you understand a black hole. There is no actual proof that light, is in fact captured by black holes !

There is no experimental proof, that's true. But every theory says that it is so.
If we admit the existence of black holes, then we have to admit there is one in our galaxy's centre and there is nothing emitting light there so...

#### DoctorBeaver

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##### If light has no mass how can black holes capture it?
« Reply #6 on: 14/09/2008 12:47:48 »
Alberto - it is certainy true that what evidence we have points strongly to there being a black hole at the centre of the galaxy; but there is no definitive proof per se.

#### ukmicky

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##### If light has no mass how can black holes capture it?
« Reply #7 on: 14/09/2008 13:49:35 »
Doc
The speed that stars can be seen orbiting the centre of the galaxy points to a something of extreme mass that could only be a SMBH, either that or it would have to be something new to science.

Quote
If light has no mass how can black holes capture it?
Because the mass of a black hole bends space .Gravity has no direct effect on light as the photon contains no mass, Gravity does however bend space.
Imagine space being a bunch of fibre optics, if all the fibre optics  started and ended inside the black hole their would be no escape for the photons traveling along them.
« Last Edit: 15/09/2008 21:19:23 by ukmicky »

#### DoctorBeaver

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##### If light has no mass how can black holes capture it?
« Reply #8 on: 14/09/2008 14:05:14 »
Doc
The speed that stars can be seen orbiting the centre of the galaxy points to a something of extreme mass that could only be a SMBH, either that or it would have to be something new to science.

Precisely - As I said, "There is no experimental proof, that's true. But every theory says that it is so."

We cannot rule out all the impossibles it we don't know what all the impossibles are.

#### lightarrow

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##### If light has no mass how can black holes capture it?
« Reply #9 on: 14/09/2008 16:58:54 »
Alberto - it is certainy true that what evidence we have points strongly to there being a black hole at the centre of the galaxy; but there is no definitive proof per se.
Ok Sir!

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##### If light has no mass how can black holes capture it?
« Reply #9 on: 14/09/2008 16:58:54 »