[imatfaal]

granpa, on 14 November 2011 - 03:32 PM, said:

the correct solution is, as I said before, that gravitational time dilation causes time to stop at the event horizon.

That is no solution. Firstly the time slows massively when viewed by those in an external accelerated frame and not for those in free fall along side at the same gravitational potential. Secondly you have your coordinate system wrong if you come up with infinite time dilation - near a blackhole's event horizon you should be using Kruskal-Szekeres coordinates, or Eddington-Finkelstein coordinates - these avoid the mathematical singularites that schwarzchild coordinate systems throw up.

[Mystery111]

imatfaal, on 14 November 2011 - 03:43 PM, said:

That is no solution. Firstly the time slows massively when viewed by those in an external accelerated frame and not for those in free fall along side at the same gravitational potential. Secondly you have your coordinate system wrong if you come up with infinite time dilation - near a blackhole's event horizon you should be using Kruskal-Szekeres coordinates, or Eddington-Finkelstein coordinates - these avoid the mathematical singularites that schwarzchild coordinate systems throw up.

You don't need to explain yourself. Bottom line is, he is wrong.

[granpa]

for those that actually want to learn
here is an explanation showing how general relativity is derived from special relativity.


math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

The Relativistic Rocket

Below the rocket, something strange is happening...

everything in the universe is falling "below" the rocket, but never receding any farther than a distance of -c2/a as measured by you. It all piles up just short of this distance, asymptoting to a plane called a horizon. You see this horizon actually form as the rocket accelerates, because there comes a time when no signal emitted from "below" the horizon can ever reach you. Everything falls toward that plane, and as it does so it begins to redden, due to the increasing red shift of its light, because you are accelerating. Finally it fades out of visibility. In fact, as anything gets closer to the horizon, it ages more and more slowly; time comes to a complete halt there.

This post has been edited by granpa: 14 November 2011 - 06:57 PM

[Mystery111]

I will later. Doctor rocket is not the be all and end all.

[morgsboi]

Mystery111, on 14 November 2011 - 02:10 PM, said:

The simple reason can be explained in a simple way.

You require energy to leave the earths atsmosphere. This is because gravity is pulling your object (the mass of the earth) from your located origin. What if that mass became so dense that the radial force required to leave your origin became that of the speed of light?

Simply, a particle of light cannot escape something when the escape velocity exceeds the speed of light.

So if nothing is faster than light, then why would physics allow a force that pulls stronger than light can travel?

[questionposter]

morgsboi, on 13 November 2011 - 11:45 PM, said:

But how can even the most extreme gravity affect something that has no mass?
And according to Professor Stephen Hawking, even a black hole is not truly black so it must emit something.

Well, I guess we can't answer "why" to a great extent but there are experiments that prove it. The best bet is that light follows the curves in the fabric of space too. Why this happens isn't answered right now.

[morgsboi]

questionposter, on 15 November 2011 - 01:54 PM, said:

Well, I guess we can't answer "why" to a great extent but there are experiments that prove it. The best bet is that light follows the curves in the fabric of space too. Why this happens isn't answered right now.

Ah, I understand. Do you know the proper name for the curves? For research purposes. Thank you

[IM Egdall]

[quote name='morgsboi' timestamp='1321387106' post='638727']
Ah, I understand. Do you know the proper name for the curves? For research purposes. Thank you
[/quote

The path of light (and everything else like planets, comets, etc.) is "bent" in a gravitational field because of the warping of space and the warping of time due to the presence of mass/energy (the source of gravity.) This warping of space and time is called spacetime curvature.

This post has been edited by IM Egdall: 15 November 2011 - 11:39 PM

[morgsboi]

[/quote

The path of light (and everything else like planets, comets, etc.) is "bent" in a gravitational field because of the warping of space and the warping of time due to the presence of mass/energy (the source of gravity.) This warping of space and time is called spacetime curvature.
[/quote]
Okay, thankyou

[A Tripolation]

I was under the impression that light didn't escape a black hole because of the fact that it was redshifted out of existence. Is this incorrect?

Ah, nevermind. That's just the way that it appears to any observer beyond the event horizon. My mistake.

This post has been edited by A Tripolation: 16 November 2011 - 01:10 AM

[The time Traveller]

questionposter, on 12 November 2011 - 01:56 AM, said:

Light is not matter, it has no mass, it's primary composition is just energy, and energy is another form of matter and vice versa. Both are effected by the fabric of space and they both effect the fabric of space. Light can't escape from a black hole simply because the gravity of a black hole is too powerful, it creates a gravitational well so steep not even light has enough speed to escape it.

As far as scientists can tell, nothing comes back from the event horizon except perhaps whatever the result is of black hole evaporation. Once light passes the event horizon, it doesn't come out. Black holes don't emit optical photons, so they are the color of black.

When light passes a large body in the universe the gravity of the said mass causes the light to bend and curve around the mass

so in theory the light adjacent to the light that has just curved around the mass will be travelling faster as the curved light has travelled a greater distance

so there for one or the other would have had to of travelled at a different speed

its not possible for some thing travelling at a constant to cover a greater distance eg the straight line is say 500.000miles and the curved line is 510.1740 miles

how can something with the same speed and velocity cover two different distances at the same time and speed QED

[JohnStu]

They say a wormhole is created

[RichIsnang]

@the time traveller, do you know for a fact that these two light rays will arrive at the same time? If so, just speculation, you may need to look at the 'amount of space' on the curved path, as spacetime is curved by the massive body, space-time is curved round it so i can only imagine that the distance from one end to another may be 510.174 but a meter may be slightly smaller in the hugely curved regions.
Einsteins theory of gravity tells us why massless particles like photons effected by gravity, it is not an attraction of the matter as such, it is just spacetime is bent around the matter, and as photons are in our time and space, their paths get curved too.
The curvature of space-time at the event horizon will cause all matter and energy to accelerate towards the black hole at the ~3x10^8ms^-2, regardless of if it has mass or not

[questionposter]

morgsboi, on 13 November 2011 - 11:45 PM, said:

But how can even the most extreme gravity affect something that has no mass?

Because energy and mass are equivalent. In fact, I think photons distort the fabric of space even easier than matter. Both matter and energy responds to distortion in the fabric of space.

This post has been edited by questionposter: 21 March 2012 - 11:29 PM

[morgsboi]

questionposter, on 21 March 2012 - 11:29 PM, said:

Because energy and mass are equivalent. In fact, I think photons distort the fabric of space even easier than matter. Both matter and energy responds to distortion in the fabric of space.

Yeah, I actually don't remember making that post. :S if it were possible to see, I wonder what light would look like in a singularity.
So what makes you think photons distort the fabric of space easier than matter?

[questionposter]

The time Traveller, on 8 December 2011 - 11:42 PM, said:

When light passes a large body in the universe the gravity of the said mass causes the light to bend and curve around the mass

so in theory the light adjacent to the light that has just curved around the mass will be travelling faster as the curved light has travelled a greater distance

so there for one or the other would have had to of travelled at a different speed

its not possible for some thing travelling at a constant to cover a greater distance eg the straight line is say 500.000miles and the curved line is 510.1740 miles

how can something with the same speed and velocity cover two different distances at the same time and speed QED

The speed of light is always constant as far as we can tell, and I think your getting measurements mixed up where they shouldn't be. Prior to measurement or direct interaction with objects, light doesn't "take" two paths, it simply "is" those two paths and an infinitesimal amount of paths in between, and this is due to its wave nature which I think is known as "superposition". After measurement, we measure that the photon's probability has collapsed down to a single interaction point for which it has transferred energy. However, after a photon has been "measured", it doesn't keep going as some point, if it's measured then it pretty much is absorbed in some way and no longer exists as that photon. In fact, I think it's impossible to directly measure a photon without destroying it. Even if an electron jumps right back down to its original energy level, it's still emitting a different photon.

So when a photon is altered by the black hole, it's not two individual photons, it's the same entire photon who's probability spans over 3-dimensional changing its shape.

This post has been edited by questionposter: 22 March 2012 - 01:41 AM

[granpa]

the speed of light is constant as measured by a local observer

however due to gravitational time dilation it is possible for the speed of light as measured by a distant observer outside the gravity well to be less than c

[Spyman]

granpa, on 22 March 2012 - 10:59 AM, said:

the speed of light is constant as measured by a local observer

however due to gravitational time dilation it is possible for the speed of light as measured by a distant observer outside the gravity well to be less than c

AFAIK, the gravitational time dilation does NOT have an effect on the measured speed of light for any observers.

[granpa]

http://en.wikipedia....l_time_dilation

The speed of light in a locale is always equal to c according to the observer who is there. The stationary observer's perspective corresponds to the local proper time. Every infinitesimal region of space time may have its own proper time that corresponds to the gravitational time dilation there, where electromagnetic radiation and matter may be equally affected, since they are made of the same essence (as shown in many tests involving the famous equation E=mc2). Such regions are significant whether or not they are occupied by an observer. A time delay is measured for signals that bend near the Sun, headed towards Venus, and bounce back to Earth along a more or less similar path. There is no violation of the speed of light in this sense, as long as an observer is forced to observe only the photons which intercept the observing faculties and not the ones that go passing by in the depths of more (or even less) gravitational time dilation.


If a distant observer is able to track the light in a remote, distant locale which intercepts a time dilated observer nearer to a more massive body, he sees that both the distant light and that distant time dilated observer have a slower proper time clock than other light which is coming nearby him, which intercepts him, at c, like all other light he really can observe. When the other, distant light intercepts the distant observer, it will come at c from the distant observer's perspective

[Spyman]

granpa, on 22 March 2012 - 11:44 AM, said:

http://en.wikipedia....l_time_dilation

The speed of light in a locale is always equal to c according to the observer who is there. The stationary observer's perspective corresponds to the local proper time. Every infinitesimal region of space time may have its own proper time that corresponds to the gravitational time dilation there, where electromagnetic radiation and matter may be equally affected, since they are made of the same essence (as shown in many tests involving the famous equation E=mc2). Such regions are significant whether or not they are occupied by an observer. A time delay is measured for signals that bend near the Sun, headed towards Venus, and bounce back to Earth along a more or less similar path. There is no violation of the speed of light in this sense, as long as an observer is forced to observe only the photons which intercept the observing faculties and not the ones that go passing by in the depths of more (or even less) gravitational time dilation.


If a distant observer is able to track the light in a remote, distant locale which intercepts a time dilated observer nearer to a more massive body, he sees that both the distant light and that distant time dilated observer have a slower proper time clock than other light which is coming nearby him, which intercepts him, at c, like all other light he really can observe. When the other, distant light intercepts the distant observer, it will come at c from the distant observer's perspective

I stand corrected, the distant observer can't see the curving of space and therefore the distance covered by light seems shorter for him.

This post has been edited by Spyman: 22 March 2012 - 12:44 PM