Two stupid questions:
(There are no stupid questions, only stupid people who ask them :rolleyes:)

When light encounters a black hole, what exactly happens?

Is it bent so severely by the gravitational field that the photons cannot escape?

My second question is, does a gravitational field that does this violate relativity theory? I thought that nothing could exceed the speed of light, but here is somthing stronger than the speed of light.....

"My second question is, does a gravitational field that does this violate relativity theory? I thought that nothing could exceed the speed of light, but here is somthing stronger than the speed of light....."

it is said that their velocity changes, so no violation of relativity
the second part i don't get:
force <--> speed of light ... doesn't make sense
besides, many people here will start telling you about space curvature here
photons follow the shortest way
there is no force involved

Light, which is comprised of photons, follows geodesic paths; ie straight lines. Massive objects such as black holes bend the space around it such that the paths, or straight lines the photons travel, are bent so severely they are warped back towards the mass and wrapped around it. Hence the photons travel these paths back towards the mass.

This does not violate any laws because the photons are still traveling at c.

Originally posted by Xev
Two stupid questions:
(There are no stupid questions, only stupid people who ask them :rolleyes:)

There are no stupid questions, only stupid answers.


When light encounters a black hole, what exactly happens?

Courts out on that one, Q's answer is a good one, as is C'est Moi's, except that a force is involved.


Is it bent so severely by the gravitational field that the photons cannot escape?

That's right.


My second question is, does a gravitational field that does this violate relativity theory? I thought that nothing could exceed the speed of light, but here is somthing stronger than the speed of light.....

I'll go aginst the grain here, inside the event horizon of a black hole Relativity is probably violated.

Is this a problem, no! In the same way that Einstein supplants Newton in extreme cases, a newer theory will supplant Einstein. Hopefully it will explain the guts of black holes.

Xev,

To answer your second question, if light had an infinite mass, and if it travelled at the speed of light at the same time, nothing could stop it. Not even black holes.

But, light does not have infinite mass. The mass of a particle of light is very small(some people on this board will tell you that light has no mass), so the gravity from a blackhole can curve lights path even though it travels at such a high speed.

Tom

some people on this board will tell you that light has no mass

Others will tell you light has mass, however when questioned as to where this mass is and what happens to it, cannot account for said mass.

If I am following your argument, light takes a curved path in a gravitational field beacuse it has mass, that mass is extremely small. So what of larger masses?

That is, by your reasoning a larger mass will take a more curved path in the same gravitational field, yes?

If so, that would give a severely different spectrophraphic signature as larger mass objects would be accelerated more. So why is this not seen?

Light can be thought of as both photons and waves, right?

Photons do not have mass, correct? Neither do waves, correct?

So, light does not have mass.

But energy and mass are interrelated.....and light is energy, for it is radiation.....

Thanks, c'est moi, Q, Thed and Joe. That clears a lot up for me.

Thed,

"If I am following your argument, light takes a curved path in a gravitational field beacuse it has mass, that mass is extremely small. So what of larger masses?

That is, by your reasoning a larger mass will take a more curved path in the same gravitational field, yes?

If so, that would give a severely different spectrophraphic signature as larger mass objects would be accelerated more. So why is this not seen?"

You surprise me. I thought you knew this!!! The answer is:

Because the mass in the acceleration formula eliminates the mass in the force formula. That is why all mass accelerates at the same rate towards Earth.

Thed, this is elementary school physics. If you still don't understand, I can show you the formulas.

Tom

Xev,

You have to consider that we are discussing particle physics. Particle physics is still mostly theoretical. You can't touch and feel a particle of light or an electron, you have to measure them indirectly most of the time. These indirect measurements are one of the reasons that there are so many different theories regarding subatomic particles. The true answer is that we don't know, we are just making educated guesses.;)

Tom

Because the mass in the acceleration formula eliminates the mass in the force formula. That is why all mass accelerates at the same rate towards Earth.

I thought Newtonian physics broke down at speeds as high as c?

you are delibrately obfuscating.

Just answer the question, does a larger mass see a larger curvature of spacetime?

Thed,

No it does not

Force=g*mass1*mass2/d^2

A of mass2=Force/mass2

When you replace "Force" in the second equation
with "g*mass1*mass2/d^2"

You get :

A of mass2=g*mass1/d^2

As you can see, mass2 is eliminated from the formula. In other words, acceleration is NOT dependent on mass2

Tom

Xev,

Maybe it does, but in the previous post I was describing mass that is moving much slower than c.

Tom

But we are not talking about acceleration. Does a larger mass cause more curvature of spacetime, than a smaller mass?

Yes or no.

Q,

I apoligize that I didn't answer your question, but I'm being bombarded by questions from all sides.

So, what does happen to the mass of a photon...

I'm not sure, under certain circumstances the photon would bounce of the particle keeping it's mass intact. At other times, it might be absorbed by the particle and the mass of the photon gets added to the mass of the particle. Or there's absorption, but the photons mass gets converted to energy.

I'm really not sure. I never thought about it.

Thed,

I DO NOT believe in the curvature of space. No mass can cause the space to curve. What you call curvature, I see as the result of gravitational force, and inertia.

Tom

Xev, interesting question…here’s a link http://www.astronomical.org/astbook/blkhole.html

Xev,

Some of the previous responses are confusing.

Black holes are a creature of relativity, and so can only be explained in the context of relativity. Newtonian explanations do not apply. The spacetime both inside and outside a black hole is well described by general relativity.

What happens inside the event horizon of a black hole is that all possible trajectories in spacetime, for every particle and for light, lead to the singularity at the centre of the hole. Once you're inside the event horizon, you <i>must</i> hit the singularity. In fact, no outwards radial motion is possible due to the extreme warping of spacetime.

Light still travels at its normal speed, but its path through spacetime becomes constrained by the geometry of the hole so that it (along with everything else) cannot escape once it crosses the event horizon.

Xev,

Be carefull!! Some of the people on this board believe that theoretical physics and real physics are the same thing.

You can recognize these people by their attempt to illustrate that they know everything(like what's inside a blackhole).

Tom

Some of the previous responses are confusing.

Hmmm... perhaps the rest of us will just keep quiet and allow James R to answer all the questions. :D

Tom

You claim not to accept the curvature of space and wrote


Originally posted by Joeblow93132
Xev,
But, light does not have infinite mass. The mass of a particle of light is very small(some people on this board will tell you that light has no mass), so the gravity from a blackhole can curve lights path even though it travels at such a high speed.


What's it to be, does light curve in a gravitational or not. If it curves please show how it does.

Thed,

A photon's path DOES curve in a gravitational field. But the space itself is NOT curved. The curving of the photon's path is the result of the attractive forces of gravity, not the curvature of space.

An electron's path curves in an electric or magnetic field. But neither the magnetic, nor the electric fields, curve space either.

Tom

Originally posted by Joeblow93132
Thed,

No it does not

Force=g*mass1*mass2/d^2

Errr, g is specific to the Earth. G is the Universal constant. But that is the smalest mistake you make.


A of mass2=Force/mass2

So the acceleration of a mass depends on force divided by the mass. Even allowing for a typo a 14 year old should know that is wrong.


When you replace "Force" in the second equation
with "g*mass1*mass2/d^2"

Let's, it's fun.

You get from you last moronic attempt.

"Force"= g*mass1*mass2 / d^2

And from the first equation

Force = g*mas1*mass2 / d^2

Now where I come from this means,

g*mas1*mass2 / d^2 = g*mas1*mass2 / d^2

Or 1 = 1

Your derivation,


You get :

A of mass2=g*mass1/d^2

As you can see, mass2 is eliminated from the formula. In other words, acceleration is NOT dependent on mass2

Tom

Is not right.

Even allowing for the odd foul up, I make them, you can not, using any known Newtonian Physics, get the result you get.

Give it up, you have no clue, what so ever.

Originally posted by Joeblow93132


Nothing that made any sense.

*PLONK*

Thed,

We can have intelligent discussions, or not.

I'm wondering if your hard-headed, or are you just a liar?

F=m*a

Look it up in your physics textbook. Therefore:

a=F/m

The greater the force, the smaller the mass, the greater the acceleration.

I sure hope that you understand this.

Don't think that I'm the only one seeing your messed up posts, everyone else sees them too.

Note to everyone: If anyone besides Thed thinks that the formulas F=m*a or a=F/m are wrong, pleae let me know.

Tom

The original question seemed to be about whether objects of different masses and traveling at the same velocity would have the same trajectory in a gravity field. From this hamster’s understanding they would. Even without Newtonian physics one might see this by considering an orbiting mass that splits into two pieces. Having less mass doesn’t mean the individual pieces will change orbit.

(An advantage to being a hamster is that no one expects a hamster to be right all the time.)

everyone knows acceleration is independent of the mass (see our dear old Galileo and the tower of Pisa ...)
orbitting a planet or sun is the same as falling
the mass has again no influence on this

Tom,

I do not know everything, but I do know the internal geometry of a black hole. I know the Schwarzschild solution of the Einstein field equations.

Your attempt to distinguish theoretical physics from what you call "real physics" just shows that you don't know what physics is.

OK, now this is probably a daft question but please try to contain your laughter. I know the answer will probably seem obvious once I read it but it's been at the back of my mind for a few years, so here goes.....

One of the classic event horizon descriptions for black hole singularities describes a spaceship falling into a black hole whilst being observed from a safe distance. As the ship falls towards the hole it appears (to the observer) to slow down until it's image remains, eternally unmoving, at the event horizon. If this is the case, should light not also be visible at the event horizon? and if so, should black holes not appear to be surrounded by light?

I may have already answered this for myself but it never hurts to get a second opinion and anyway, the general level of discussion here proves that at least you guys think!

Ha ha ha. You must not be referring to me.

I think that the light must be completly distorted by the gravitational feild, so that it is, in effect, completly pulled into the black hole.

I do not think that an image would linger.

You will see the ship moving slower and slower as it approaches the event horizon but you will never actually see the ship reach the event horizon no matter how long you watch it. The ship however, will pass the event horizon in a matter of minutes and will be crushed a few seconds later.

Okay, then, why don't we see this optical illusion with light?

And what causes this illusion? Anybody know?

Actually Q, that depends on the faith of the universe. :)

The ship at the event horizon freezes and time stops. In the ships reference system it will see a fast forward movie of the outside universe. It could very well happen that the whole universe collapses into a big crunch before the ship falls into the hole. That is, if one beleaves in the big crunch theory.

[QUOTE]Originally posted by James R
[B]
What happens inside the event horizon of a black hole is that all possible trajectories in spacetime, for every particle and for light, lead to the singularity at the centre of the hole. Once you're inside the event horizon, you <i>must</i> hit the singularity. In fact, no outwards radial motion is possible due to the extreme warping of spacetime.
QUOTE]

May I ask if all paths lead to the singularity inside the event horizon what happened to the path leading into the event horizion, say for example a space ship where to be drawn into the blackhole and an ocuppant of the ship tried to shine a high beam light to the outside world why cant the light travel through the path in which the ship entered into the blackhole, the path does not just disapear does it ?

I mean im imagining the path into the singularity as a cone and if it can come in then why cant it get out ?

Do you imagine it as a ball rolling into the hole but not being able to roll out again because towards the singulairty space time is curved so steep that light can not travel up this path ?

Im not a scientist im actually a software engineer but i have intrest in this kind of thing so please be kind in your responses, thanks.

Also one more thing,

Im looking at the diagram given in this url
http://www.astronomical.org/astbook/blkhole.html

diagram Figure 5: Space-time diagram (11)

Can someone explain to me what this diagram means because to me it doesnt make much sense, if the y axis is time and the x axis is your location in space this shows you can be in 2 places in space at the same time :confused: how can this be possible ?

and the figure :

Figure 6: Penrose Diagram of Schwartzchild Black Hole (13)

I dont understand this one at all can someone do a brief explanation of it.

Thanks

Also one more thing,

Im looking at the diagram given in this url
http://www.astronomical.org/astbook/blkhole.html

diagram Figure 5: Space-time diagram (11)

Can someone explain to me what this diagram means because to me it doesnt make much sense, if the y axis is time and the x axis is your location in space this shows you can be in 2 places in space at the same time :confused: how can this be possible ?

and the figure :

Figure 6: Penrose Diagram of Schwartzchild Black Hole (13)

I dont understand this one at all can someone do a brief explanation of it.

Thanks

Xev

As the ship approaches the black hole it takes longer and longer for the light to climb out and reach the observer. At the event horizon, the light will virtually hover in place.

Also, time slows down at the event horizon. If the ship hovered at the event horizon and then somehow managed to escape, all onboard would have aged less than the outside observer.

From what I understand the following occurs:

Light in wave formation entering a blackhole is stretched to flatten, changing it's allocation within the spectrum to a lower an lower frequency. (you can think of this as a wave formation flattening)

While the blackhole itself has a similar effect happening, as many have mentioned it's gravity creates a spacial distortion that people call "bending". This bending isn't caused just by gravity of matter and electromagnetics, but because a blackhole exists (As James R mentioned I think) as a Singularity at its centre.

This means that the distance on the way to a blackholes centre actually passes through different universal "Times", that can as a counterpart of a paradox causing parallels.

Since there are a multiple number of universes existing in coelation, the combine gravity is stronger than any other point in the universe.

This gravity is enough to distort timespace, so that light is no longer travelling through normal space but one that begins to ebb and flow much like a wave formation as it gets nearer to the centre of a blackhole. *These bends Deposit the red spectral light at other universal points, possible making up zero-point, due to it being at such a low scale.

This means that to an observer, an object wouldn't just slows as it enters a blackhole, but it would begin to resonate and fluctuate between different universe faster and faster until it's destroyed.

*edited

tallest,

The reason you don't see the images of stuff hovering forever near the event horizon of a black hole, or see the event horizon as surrounded by light, is that light climbing upwards from the event horizon is red-shifted by the gravitational field. Light <i>at</i> the event horizon is red-shifted to zero frequency and zero energy as it climbs out of the hole, so by the time it reaches your eyes, there's nothing to see any more.


malisha:

Figure 5 is a spacetime diagram. The location of any <b>event</b> is a dot on the diagram. It does not indicate that you can be in two places at once.

The intersection of the space and time axes is the point we call "now". The angled lines are the paths that light would take if emitted from the origin of the graph. Any object with mass can trace out a path in spacetime in the "permitted" region between the light paths, but can never get from the origin to any of the "forbidden" regions. The "permitted" region is often called the <b>forward light cone</b> of the point at the origin. An event at the origin can only effect things which are in its forward light cone. It can have no contact with anything in the "forbidden" region.

Figure 6 is a special type of diagram showing regions of spacetime near a balck hole. Once a particle from our universe crosses the event horizon, it can only travel with its forward light cone (from the point where it crosses). Notice that since it must always go forwards (in time), it <i>must</i> hit the singularity. It can never leave the inside of the hole once it has crossed the horizon.

James R, I thank you.

Red-shifting was the answer that I had come up with but it seemed to contradict the old spaceship description (which I realise is just an educational tool to help people grasp a v. difficult concept). However, if light gets progressively more and more red-shifted until it reaches zero-frequency and zero-energy at the event horizon should there not exist a sphere of points at some distance from the horizon where light can escape the gravitational pull in visible form?

tallest,

Yes, light can escape in visible form from anywhere outside the event horizon, but the closer it is to the event horizon when it starts the more red shift it gets on the way out.

The accretion discs surrounding black holes pump out a hell of a lot of energy in the form of light - mostly high energy gamma rays.

But James,How does light cross the Event Horizon?:confused:


bye!

Zion

Light can't cross the event horizon. After the ship crosses the event horizon, the light emitted will not reach the outside observer.

Prior to the ship crossing the event horizon the visible light wavelength will get longer and longer to the point of no longer being visible to the outside observer, but will instead become infrared radiation and then radio waves.

(Q),

I'm sure that many people have indicated that the spacial distortions of a blackhole (The bends of space, that shift between times and universes) can have the light escape as a deposit.

In fact there is even question over the possibility that zero-point could have been created from this depositing.

(namely the light stretches into a bend, and finds itself no longer in the same timespace as the blackhole, but a completely different universal positioning)

zion,

No light can travel from inside the horizon to the outside. Of course, there's no problem with going the other way.

As one might expect, James R. gave a lucid explanation of how the intense gravity red shifts light, making an object dimmer and dimmer as it approaches the event horizon.

In theory, time contraction effects result in matter never passing through the event horizon in the time frame of distant observers. In practice, the red shift described by James R. indicates that a distant observer will never see either light or any material pass through the event horizon. However, black holes expand in finite time if there is matter for them to suck in. I think this occurs because the event horizon expands in finite time as matter is sucked in. Consider the following.

At a given time, suppose R is the radius of the event horizon. Matter is being sucked in from the volume of space surrounding the event horizon. What happens if the matter between R & R+Delta combined with the matter already in the black hole is sufficient to create a black hole with event horizon R+Delta? It seems to me that the event horizon expands to R+Delta.

I believe that a distant observer can see the event horizon growing if huge amounts of matter are being sucked into the black hole, even if he cannot see any object actually passing through an event horizon. In a sense, it seems to me that an object can get beyond an event horizon in finite time relative to the framework of a distant observer.

The space curvature concept is a mathematical model. The mathematics of general relativity presents the laws of physics in a manner such that the trajectories of particles look like static geometric objects in a curved 4D space. If you do not like the concept of curved space, you do not have to accept it. The mathematics, however, looks like the mathematics of curved 4D space. It is analogous to using complex number operations to model 2D vectors. You might not like or believe in complex numbers, but the mathematics is useful. I find myself not quite believing that minus numbers have a square root, but I have learned to live with the idea and use the pertinent mathematics for practical purposes.

I have no idea what the relativistic equations look like for gravitation computations. I am sure that they are only approximated by F=GMm/d^2 & F=ma of classical physics. For dealing with black holes, I would not trust any conclusions based on the classical formula.

While I would expect all the matter inside the event horizon to end up at the center, I think that different configurations are at least temporarily possible.

I cannot imagine circumstances causing other configurations in practice, but in theory they seem feasible.

Prior to acceptance of the current Big Bang theory and recent advances in cosmology, I think serious physicists claimed that our universe could be the interior of a black hole. I heard it said that the density of matter inside a large event horizon need not be incredible. Perhaps I misunderstood or misremember such statements, but I think they were made by men who knew how to do the relativity mathematics.

Note that inside a hollow spherical shell, there is no gravitational force due to the shell itself. This implies that matter recently sucked past the event horizon need not result in gravitation force on anything deeper in the interior of the black hole. While it does not seem possible in practice, it seems theoretically possible for thermonuclear processes (and rotational effects) to create a temporary situation inside the event horizon such that most of the matter is not at the center. It even seems possible for there to be regions within which gravitational forces are not incredibly strong.

It seem to me that a black hole could theoretically be created by some implosion process applied to a huge cloud of gas with sufficient mass to make a black hole with a large event horizon. There could be a short period of time when a region at the center was subject to hardly any gravitational force, even though a black hole with an event horizon had been formed.

Originally posted by Joeblow93132
Thed,

I DO NOT believe in the curvature of space. No mass can cause the space to curve. What you call curvature, I see as the result of gravitational force, and inertia.

Tom

Measurements by the Viking spacecraft published in 1976 confirmed to a high degree of accuracy that space becomes non-euclidean in the vicinity of the Sun. Signals between Earth and the spacecraft had to travel an extra 37 kilometers in the 378 million kilometer separation.

Apparently, if you physically measure the ratio between a circle's circumference and diameter in the vicinity (or inside) of the sun, it will be slightly less than pi. That is, the diameter is more than it should be compared to the circumference.

See http://online.kitp.ucsb.edu/online/bh_teach --
the Viking factoid is from slide 7 of Kip Thorne's talk. But I don't believe what he says about the inside of black holes!