What? (Event Horizon)

[Zain Adeel]

Effect of Light on Event Horizon

why does the light slow does????

shouldnt it stay constant??

or perhaps speed up because of the gravitational pull of the black hole?

And does it just slow done for the observer? If yes then why do u see it slow down?

need an explanation.. im having a headache..

[LOC Veteran]

You should def. ask to have this moved to the science forum my friend. You will get many more responses there especially about this topic.

[Pong]

Effect of Light on Event Horizon

why does the light slow does????

shouldnt it stay constant??

or perhaps speed up because of the gravitational pull of the black hole?

And does it just slow done for the observer? If yes then why do u see it slow down?

need an explanation.. im having a headache..

It slows down because it is being accelerated in the opposite direction from the observer (i.e. towards the black hole), if that makes sense to you. It's being pulled towards the black hole and thus slowed down but not enough to make it actually move towards the black hole.

Edit to try and make it clearer:

Imagine you can only swim at a fixed rate and are placed in a river trying to swim away from a water fall. The closer you get to the edge the faster the water flows (in a black hole the water is actually space itself) and although you are still swimming at the same rate you do not travel as fast because the water is moving in the opposite direction, effectively slowing you down.

The event horizon itself is the point where the water is moving in the opposite direction at exactly the same rate that you are able to swim and hence you cannot escape.

Edited December 17, 2009 by Pong

[Zain Adeel]

well i didnt include this but the problem is that light isnt going away from the black hole.. but going INTO THE BLACKHOLE..

so shouldnt it speed up because of the gravity?

go to wikipedia and look for red shift..

and ull see a pic..

its confusing me

[Laurë Veteran]

Thread moved.

[Zain Adeel]

thank u for moving the thread i just didnt see that the science section was not just for the news.

[rob.derosa]

well i didnt include this but the problem is that light isnt going away from the black hole.. but going INTO THE BLACKHOLE..

so shouldnt it speed up because of the gravity?

go to wikipedia and look for red shift..

and ull see a pic..

its confusing me

Light has no mass, therefore it won't speed up due to gravity. Red shift is due to the change in wavelength of the light.

[Fred Derf Veteran]

well i didnt include this but the problem is that light isnt going away from the black hole.. but going INTO THE BLACKHOLE..

so shouldnt it speed up because of the gravity?

go to wikipedia and look for red shift..

and ull see a pic..

its confusing me

Do we see the actual light or do we just see the reflection of the light? Perhaps that is why it is the opposite.

What we perceive as light has to travel back to our eyes so that we can see it. If that is being pulled away from us and towards the black hole then we would see that acceleration away from us as a slowdown.

[rob.derosa]

Do we see the actual light or do we just see the reflection of the light? Perhaps that is why it is the opposite.

What we perceive as light has to travel back to our eyes so that we can see it. If that is being pulled away from us and towards the black hole then we would see that acceleration away from us as a slowdown.

No, I don't think so. The 'light' from a black hole is usually caused by X-ray emissions from extreme interactions within the accretion disc around the black hole. Light can't bounce off the black hole to be reflected back to us.

[Fred Derf Veteran]

Light has no mass, therefore it won't speed up due to gravity. Red shift is due to the change in wavelength of the light.

I'm no physicist but the normal rules of spacetime would seem to not always apply to black holes. They are called black holes because light cannot escape and so we cannot actually see what they look like. Light acts as both a wave and a particle so some part of it mush have a minimal mass that we cannot detect or else light would be able to escape a black hole.

[christracy]

Looking at the pic and reading the wiki entry Rob has the right idea. Blue light is the shorter wavelength as the light wave gets to the event horizon the black hole is pulling the light toward it and elongating the wavelength which makes the light red.

[rob.derosa]

I'm no physicist but the normal rules of spacetime would seem to not always apply to black holes. They are called black holes because light cannot escape and so we cannot actually see what they look like. Light acts as both a wave and a particle so some part of it mush have a minimal mass that we cannot detect or else light would be able to escape a black hole.

It has zero mass. If photons had mass the laws of physics would break down. Light cannot escape a black hole because the escape velocity of the event horizon is larger than the speed of light.

[Fred Derf Veteran]

It seems that you are thinking of an older Newtonian view of gravity where light is not affected by gravity.

According to Newtonian gravity, light is not affected by gravity, as light is massless. Einstein's law E = mc2, immediately suggests that light is affected by gravity. This is indeed the case and has experimentally be observed via gravitational lensing and other effects.

http://www.physlink.com/Education/AskExperts/ae661.cfm

[rob.derosa]

It seems that you are thinking of an older Newtonian view of gravity where light is not affected by gravity.

http://www.physlink.com/Education/AskExperts/ae661.cfm

Yeah, that wasnt correct on my part, but it is the case that light will not speed up.

The reason light is effected by gravity is the warping in spacetime caused by the mass of the blackhole. Within the event horizon all paths on the surface of space time lead back into the black hole. You cannot escape.

[vincent]

Yeah, that wasnt correct on my part, but it is the case that light will not speed up.

The reason light is effected by gravity is the warping in spacetime caused by the mass of the blackhole.

This is correct. And it also explains Gravitional Lensing

Within the event horizon all paths on the surface of space time lead back into the black hole. You cannot escape.

Yup.

[Fred Derf Veteran]

My original point, however, was that we don't see the photons as they travel through space. We see the reflections that cause them to head back towards us. Some light must be reflected/refracted from outside the event horizon before it gets caught inside. That must be what we see (presuming that we can see anything).

[sonrah]

well i didnt include this but the problem is that light isnt going away from the black hole.. but going INTO THE BLACKHOLE..

so shouldnt it speed up because of the gravity?

go to wikipedia and look for red shift..

and ull see a pic..

its confusing me

The thing about light is that it doesn't "speed up" when inside some other thing, at least according to my Physics teacher. For example, if I shine a light from inside a moving car, and when I'm stationary, then both lights are moving at the speed of light. The first one isn't moving at the speed of light + the speed of the car.

[rob.derosa]

My original point, however, was that we don't see the photons as they travel through space. We see the reflections that cause them to head back towards us. Some light must be reflected/refracted from outside the event horizon before it gets caught inside. That must be what we see (presuming that we can see anything).

You don't see reflections. As I said the light we see from black holes is caused by X-ray emissions from extremely hot reactions in the accretion disk. These photons radiate in all directions, therefore we see them.

[Napalm Frog]

The thing about light is that it doesn't "speed up" when inside some other thing, at least according to my Physics teacher. For example, if I shine a light from inside a moving car, and when I'm stationary, then both lights are moving at the speed of light. The first one isn't moving at the speed of light + the speed of the car.

However, that is due to inertia acting upon a mass, not an external force acting upon it like the heavy gravitational pull. But other than that, yes, I agree, light will not speed up. I believe Fred has it correct, that the escaping light is being slowed down. What we see of the light are the rays/waves leaving the source and hitting our eyes, so something IS leaving the black hole. The only thing that boggles my mind is how gravity is actually affecting the light. I am aware that in advanced, light CAN be affected but gravity, but can't grasp HOW.

EDIT: Okay, the X-Ray light source makes sense. But how are we not seeing the light itself trapped within the event horizon?

[Fred Derf Veteran]

EDIT: Okay, the X-Ray light source makes sense. But how are we not seeing the light itself trapped within the event horizon?

In order for the light to reach our "eyes" (aka telescopes), it would first need to escape from inside the event horizon. That doesn't happen. Spacetime is too heavily warped inside the event horizon for anything to get out.

[vincent]

The Event Horizon makrs the point of no return as noted earlier the photons would need an escape velocity that is faster than light, the light we see from BH's are the x-rays from the heated gasses in the acretion disk, due to hawking radiation.

[rob.derosa]

The Event Horizon makrs the point of no return as noted earlier the photons would need an escape velocity that is faster than light, the light we see from BH's are the x-rays from the heated gasses in the acretion disk, due to hawking radiation.

Hawking radiation is nothing to do with the accretion disk, it is a quantum mechanical effect due to the capture of one component of a virtual pair of particles. So all the time countless particle-antiparticle pairs are being formed all around us, they are usually destroyed within a fraction of a second (governed by the uncertainty principle - this way it does not take any energy to create them, you are borrowing the energy from the quantum fluctuations). However, if these form near a black hole, it is possible one of the particles could be captured. This means that the second particle cannot be destroyed, and thus must be real. The energy for the creation of this particle must come from somewhere, and it is the black hole that takes the bill.

I think the temperature of a black hole, caused by Hawking radiation, is on the order of a few nano-Kelvins, impossible to cause X-Ray emissions.

[ylcard]

Hawking radiation is nothing to do with the accretion disk, it is a quantum mechanical effect due to the capture of one component of a virtual pair of particles. So all the time countless particle-antiparticle pairs are being formed all around us, they are usually destroyed within a fraction of a second (governed by the uncertainty principle - this way it does not take any energy to create them, you are borrowing the energy from the quantum fluctuations). However, if these form near a black hole, it is possible one of the particles could be captured. This means that the second particle cannot be destroyed, and thus must be real. The energy for the creation of this particle must come from somewhere, and it is the black hole that takes the bill.

I think the temperature of a black hole, caused by Hawking radiation, is on the order of a few nano-Kelvins, impossible to cause X-Ray emissions.

Err, I can't remember the exact explanation to save my life, but I've seen something about this on NGC (or was it HC?), anyway..

So basically a particle is being pulled towards the black hole and when it breaks down to two particles, one positive and one negative, one of them continues on his way to the black hole and the other one escapes it.

You seem knowledgeable, especially about all of this, so you might explain it better than I did, but that's what I vaguely remember from that show :)

I find black holes very interesting but I can't understand almost anything related to them, I mainly find the idea of being sucked down into one cool :)

[rob.derosa]

Err, I can't remember the exact explanation to save my life, but I've seen something about this on NGC (or was it HC?), anyway..

So basically a particle is being pulled towards the black hole and when it breaks down to two particles, one positive and one negative, one of them continues on his way to the black hole and the other one escapes it.

You seem knowledgeable, especially about all of this, so you might explain it better than I did, but that's what I vaguely remember from that show :)

I find black holes very interesting but I can't understand almost anything related to them, I mainly find the idea of being sucked down into one cool :)

Hm, kinda. It is not that a particle is being pulled towards a black hole, it is that a virtual particle pair (consisting of a particle and antiparticle) is produced next to the black hole. This can happen because the uncertainty theorem states that energy can be borrowed from the quantum background for a short period of time (http://en.wikipedia.org/wiki/Uncertainty_principle#Energy-time_uncertainty_principle). Now if one of these particles is captured by the black hole, they cannot destroy each other and therefore the universe is effectively owed energy. It all sounds a bit vague, but that's what happens!

The only scary thing is that due to time dilation; you would appear to an observer as to never actually reach the event horizon!

[Zain Adeel]

ok. this is not my question :p

i wasnt asking what happens inside the blackhole as we dont know yet.

But one guy really gave a good answer..

that light is pulled towards it, thus slowing it for us as we are at the opposite end of it and we see it shifting to red because of different wavelengths of different colored photos.

i seriously never get the idea of this WAVE/PARTICLE DUALITY!!!..

this is not rite..

a fruit cant be an apple and an orange at the same time..

so we are skipping alot of things about light as of yet.

oh..

and gravity does affect LIGHT:.

and thus light has MASS..

:)

else it wouldnt be pulled by gravity and their wouldnt be any gravitational lensing..

anyway.

Black holes are still a mystery if u ask me..

The only scary thing is that due to time dilation; you would appear to an observer as to never actually reach the event horizon!

I dont believe this time dilation thing..

seriously...

mayb i need a very very detailed explanation..