Most recently and over time I have viewed numerous links about what the theories of blackholes are. Some reading and utube links about the event horizon and what the singularity of the blackhole may be like as a one relevant example.

For instance the notion that blackholes are so dense at even light cannot escape. Which translates to no photons may escape a blackhole. Which in a fashion implies a gravitation well which implies mass and yet photon have no mass.

How is something without mass affected in such a way?

ratty one said:

Most recently and over time I have viewed numerous links about what the theories of blackholes are. Some reading and utube links about the event horizon and what the singularity of the blackhole may be like as a one relevant example.

For instance the notion that blackholes are so dense at even light cannot escape. Which translates to no photons may escape a blackhole. Which in a fashion implies a gravitation well which implies mass and yet photon have no mass.

How is something without mass affected in such a way?

The escape velocity of a black hole is greater than the speed of light, so photons, travelling at the speed of light cannot escape ..

The gravitational well of a black hole is left over from the huge mass that caused it

I briefly read about a Plank event within a Blackhole beyond the event horizon and the point where there is no motion at all and similar to a fixed point of density. I couldn’t find a wiki link for that bit though.

An expert like DV or BC could explain it better…

The light rays are expected to travel in circles. So that if you look in front of you, you see the back of your head.

Dropbear said:

An expert like DV or BC could explain it better…

Trying for a nibble from BC eh?

:-)

ratty one said:

Dropbear said:

An expert like DV or BC could explain it better…

Trying for a nibble from BC eh?

:-)

Trolling is anti-social, I’d never do that ;)

(Readjusts halo)

Dropbear said:

ratty one said:

Most recently and over time I have viewed numerous links about what the theories of blackholes are. Some reading and utube links about the event horizon and what the singularity of the blackhole may be like as a one relevant example.

For instance the notion that blackholes are so dense at even light cannot escape. Which translates to no photons may escape a blackhole. Which in a fashion implies a gravitation well which implies mass and yet photon have no mass.

How is something without mass affected in such a way?

The escape velocity of a black hole is greater than the speed of light, so photons, travelling at the speed of light cannot escape ..

The gravitational well of a black hole is left over from the huge mass that caused it

I read that the blackholes capture matter continue to collapse upon itself at a rate faster than the speed of light travels but could that not also mean the light has not been captured but rather never enters due to the speed differences?

ratty one said:

Dropbear said:

ratty one said:

Most recently and over time I have viewed numerous links about what the theories of blackholes are. Some reading and utube links about the event horizon and what the singularity of the blackhole may be like as a one relevant example.

For instance the notion that blackholes are so dense at even light cannot escape. Which translates to no photons may escape a blackhole. Which in a fashion implies a gravitation well which implies mass and yet photon have no mass.

How is something without mass affected in such a way?

The escape velocity of a black hole is greater than the speed of light, so photons, travelling at the speed of light cannot escape ..

The gravitational well of a black hole is left over from the huge mass that caused it

I read that the blackholes capture matter continue to collapse upon itself at a rate faster than the speed of light travels but could that not also mean the light has not been captured but rather never enters due to the speed differences?

You’ve lost me there sorry…

:)

Oh look shiny things

(Readjusts halo)

Nearly dazzled me! What is that shiny thing?

Buggrit….too slow, I was.

Dropbear said:

ratty one said:

Dropbear said:

The escape velocity of a black hole is greater than the speed of light, so photons, travelling at the speed of light cannot escape ..

The gravitational well of a black hole is left over from the huge mass that caused it

I read that the blackholes capture matter continue to collapse upon itself at a rate faster than the speed of light travels but could that not also mean the light has not been captured but rather never enters due to the speed differences?

You’ve lost me there sorry…

:)

Oh look shiny things

Photon speed.

one minute =

this distance

——————->_________________(Gravity well here)

Compared with …

Blackhole speed capturing matter within the gravity well over

one minute

this distance

—————————————————————->(Gravity well here)

In the your explanation and in the notes of the article the photos don’t escape. You described why as a possibilty.

I ask is there a possibility that the photons don’t enter the event horizon and beyond because of the speed differences?

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

That’s correct

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

I did think about light being bent in water for some reason but I thought that was for other reasons and then I would just ask the questions to understand.

Dropbear said:

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

That’s correct

Like how the spacetime collapses upon itself (that bit I remember from the link) and the light travels along some plane within the collapsing spacetime. Is that what you both mean?

ratty one said:

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

I did think about light being bent in water for some reason but I thought that was for other reasons and then I would just ask the questions to understand.

Yeah, it is another reason :) Light travels at a different speed in different mediums. Basically light will follow a path that takes the ‘least time’, not the shortest route.

ratty one said:

Dropbear said:

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

That’s correct

Like how the spacetime collapses upon itself (that bit I remember from the link) and the light travels along some plane within the collapsing spacetime. Is that what you both mean?

Light travels in straight lines in space-time. These ‘straight lines’ get bent in the presence of mass ..so even though light is still travelling in a straight line, the straight line is bent ;) (and in a black hole there is no ‘straight line’ that leads outside of the hole)

I read that the blackholes capture matter continue to collapse upon itself at a rate faster than the speed of light travels but could that not also mean the light has not been captured but rather never enters due to the speed differences?

it is a frame of reference thing. same, but opposite, of us watching an object “enter” a BH. we would see it getting redder and redder, due to gravitational time dilation (i think that is the one), but never actually cross. from the object’s frame of reference everything is normal and it crosses the EH.

soooo blackholes don’t continue to collapse, the EH isn’t moving. the EH is defined by the speed of light, it is the region where escape velocity = the SoL, as droppy (i think) has said.

Dropbear said:

ratty one said:

Dropbear said:

That’s correct

Like how the spacetime collapses upon itself (that bit I remember from the link) and the light travels along some plane within the collapsing spacetime. Is that what you both mean?

Light travels in straight lines in space-time. These ‘straight lines’ get bent in the presence of mass ..so even though light is still travelling in a straight line, the straight line is bent ;) (and in a black hole there is no ‘straight line’ that leads outside of the hole)

Good. That makes more sense.

I am still going to research more about Plank Stars forming from BH’s one theory that is linked to Hawking’s theories afaict.

talking of refraction, this is an answer KJW gave to explain it.

I really dislike this common explanation as it fails to take into account the role of the medium. When an electromagnetic field propagates through a medium, the charges in the medium move in response to that electromagnetic field. The electromagnetic field associated with the charges adds to the propagating electromagnetic field in such a way as to produce a phase delay in the propagating electromagnetic field. Thus, the change in the speed of light (which is a change in the wavelength, but not the frequency) is the result of the ability of the changing electromagnetic field to alter the charge distribution within the medium. Media with a more easily polarisable electron density therefore have a higher refractive index. The refractive index also depends on the frequency of the propagating electromagnetic field. In the visible range, only the electron density can be deformed, whereas at frequencies lower than the infrared, the charge distribution can also be altered by deforming the shape of the molecules.

I got lost at the third sentence, I think that’s a new record for me understanding a KJW post :)

Planck.

ChrispenEvan said:

talking of refraction, this is an answer KJW gave to explain it.

I really dislike this common explanation as it fails to take into account the role of the medium. When an electromagnetic field propagates through a medium, the charges in the medium move in response to that electromagnetic field. The electromagnetic field associated with the charges adds to the propagating electromagnetic field in such a way as to produce a phase delay in the propagating electromagnetic field. Thus, the change in the speed of light (which is a change in the wavelength, but not the frequency) is the result of the ability of the changing electromagnetic field to alter the charge distribution within the medium. Media with a more easily polarisable electron density therefore have a higher refractive index. The refractive index also depends on the frequency of the propagating electromagnetic field. In the visible range, only the electron density can be deformed, whereas at frequencies lower than the infrared, the charge distribution can also be altered by deforming the shape of the molecules.

pfft.

ChrispenEvan said:

Planck.

yeah that too.

> which is a change in the wavelength, but not the frequency

Whooaaa…nellie!

ChrispenEvan said:

Planck.

I can do a 1:30 Planck..

Basically he was descibing the medium was causing a change to the frequencies of the light. That is how I determined the quote Chrispen.

Which was alluded by the simple and non-related water and bending light example earlier in the thread.

That is how I understood what was said.

Dropbear said:

ChrispenEvan said:

Planck.

I can do a 1:30 Planck..

I thought plancking was so 2010.

http://en.wikipedia.org/wiki/Redshift

it’ll be one of these ratty, either expansion of space (cosmological) or gravitational.

sibeen said:

Umm, in my super dumb way I always thought that photons are still effected by gravity, even though they have no mass, because gravity bends space-time. In a black hole it is a really extreme bend.

Photons have zero rest mass. However, photons are never at rest in any inertial reference frame. So any inertial observer can assign a non-zero relativistic mass to a given photon, which will depend on the energy with which the photon was initially emitted, and on the speed of the observer relative to the light source. At least, that’s true in static, flat spacetime. In the real universe, the photon’s energy (& hence its relativistic mass) will also be modified by the curvature and expansion of spacetime.

OTOH, modern relativity tends to avoid using the concept of relativistic mass, as it can be misleading and lead to erroneous conclusions in certain situations. So in modern treatments we tend to focus instead on the idea that energy distorts the spacetime metric, i.e., it modifies the usual Pythagorean formula for calculating the spacetime interval between two events (points in spacetime). That spacetime distortion manifests as curved trajectories in space.

When calculating the trajectory of a relatively low mass body around a much more massive body, we can generally ignore the additional spacetime distortion caused by the low mass body and only worry about the spacetime distortion caused by the massive body.

So when we calculate the trajectory of a small particle around a black hole, we don’t need to worry about the mass of the small particle – we only need to know its position & velocity (in some convenient frame). So it makes no difference in such calculations if the small particle has zero mass, or merely just a very small mass.

…

OTOH, if we want to calculate what happens when two black holes encounter each other, then things get rather messy. With such orbits, we can’t approximate things in a Newtonian way, we need to use the full machinery of GR (luckily, some simplifications are possible in the early stages of such calculations, due to the spherical symmetry of the black holes). Nice, simple Newtonian-style orbits are not possible for a pair of black holes – the trajectories are somewhat chaotic. Of course, the situation gets even more chaotic when the two BHs collide. :)

I would have thought if time slows in the presence of mass, a mass so heavy that light can be captured by it would have also meant that time slows down significantly too , if the black hole is a singularity because its so heavy , wouldn’t that also mean time slows to a stop at the singularity too??

An expert like DV or BC could explain it better…
—————————————————

The escape velocity of a black hole is greater than the speed of light,
——————————————————————

Nothing has a greater speed than light…

It is better to say “There is no escape velocity”

‘DV’ circa before now…

wookiemeister said:

I would have thought if time slows in the presence of mass, a mass so heavy that light can be captured by it would have also meant that time slows down significantly too , if the black hole is a singularity because its so heavy , wouldn’t that also mean time slows to a stop at the singularity too??

Sort of. As was mentioned earlier in the thread, to a distant observer a body falling into a black hole appears to take forever to cross the event horizon, but an observer on the falling body doesn’t notice their clocks ticking slower as they cross the horizon & approach the core of the black hole. But if the falling observer looks back out at the rest of the universe, it will appear spatially distorted and sped up in time.

(If you fall into a stellar mass black hole, you’d soon get ripped to pieces by tidal forces, but if you fall into a big one (like the ones often found at the cetres of galaxies) you could cross the event horizon without being affected by tidal forces for a while).

Mathematically, you can’t legitimately convert time measurements made by an observer who has crossed the horizon into time measurements in the frame of a distant observer, but it’s sometimes said that once you’ve crossed the horizon you’re effectively infinitely far in the future relative to the outside observers.

As for what happens at the core of the black hole, we don’t yet have a theory that works in such extreme conditions. So we can’t really say how space, time, matter or energy behave there. But we’re fairly confident that normal matter particles (fermions) cannot exist there. And if spacetime itself is quantised, then normal notions of space or causality will not be applicable near the core of a black hole.

> Which in a fashion implies a gravitation well which implies mass and yet photon have no mass. How is something without mass affected in such a way?

E=mc^2 tells us that energy is mass. Photons have energy therefore they have mass and are attracted by the gravity of a black hole. What photons don’t have is “rest mass”. ie, if you could slow a photon down to a speed of zero then it would have no mass.

Just to confuse matters, physicists refer to “rest mass” as “mass” and refer to the mass from E=mc^2 as “relativistic mass”. With that nomenclature, gravity acts not on “mass” alone but on “relativistic mass”.

if you could slow a photon down to a speed of zero then it would have no mass.
————————————————————————————————————————————————————-

So how does nothing, times a lot… (of speed)

Equal something.

Still, the relativistic mass of light is pretty tiny.
Eg, the relativistic mass of all the light emitted by a 10 kilowatt source for a year is just over 3.5 milligrams.

Google Calculator says ((10 kilowatts) * 1 year) / (c^2) =
3.51118155 milligrams

Of course, no light source is perfect, so some of that 10 kW will be in the form of heat (i.e., infrared light).

Doesn’t the earth get heavier by photosynthesis?

Mr Ironic said:

if you could slow a photon down to a speed of zero then it would have no mass.
————————————————————————————————————————————————————-

So how does nothing, times a lot… (of speed)

Equal something.

Ah, but you can’t actually slow down photons – they always travel at c, relative to any observer. A photon isn’t merely nothing with a lot of speed – it’s a little chunk of energy, an excitation of the electromagnetic field, to be a little more precise.

A recent thread mentioned experiments that slow down light and even cause it to stop for some time. However, these experiments play with the group velocity of light, not its phase velocity; the true speed of the photons involved is unaffected by these shennanigans.

See Slow light

and

Subluminal which has a graphical applet illustrating group velocity & anomalous dispersion. Unfortunately, the applet requires that you enable Java (not to be confused with JavaScript) in your browser.

tauto said:

Doesn’t the earth get heavier by photosynthesis?

The Earth holds some of the EM energy it receives from the Sun, which adds a little bit to its mass; I have no idea how much of that energy is stored as chemical energy via photosynthesis, but I suspect that it’s pretty tiny compared to the total heat content.

The Earth radiates most of the EM that it receives, otherwise the oceans would’ve boiled off billions of years ago. :) It also generates some heat internally, due to radioactive decay. This radioactive heat has kept the interior hot, without it the Earth would’ve cooled down long ago, and it’d be a tectonically dead planet. But that’s a topic for another thread.

> which is a change in the wavelength, but not the frequency

PM, could you reply to that one?

sibeen said:

> which is a change in the wavelength, but not the frequency

PM, could you reply to that one?

I ignored that one

sibeen said:

> which is a change in the wavelength, but not the frequency

PM, could you reply to that one?

Speed = distance / time

so

wave speed = wavelength * frequency.

When a wave passes into a medium with a different speed it keeps oscillating at the same rate, but its wavelength changes to conform to that equation.

Does that help?

PM 2Ring said:

sibeen said:

> which is a change in the wavelength, but not the frequency

PM, could you reply to that one?

Speed = distance / time

so

wave speed = wavelength * frequency.

When a wave passes into a medium with a different speed it keeps oscillating at the same rate, but its wavelength changes to conform to that equation.

Does that help?

Actually…yes.

I wasn’t thinking it through.

As lamba = v/f then of course if the v changes the lambda will but not necessarily the frequency. Of course, anything that is plus/minus 10% of 50 Hz is not really worth talking about.

stomps off

:)

sibeen said:

PM 2Ring said:

sibeen said:

> which is a change in the wavelength, but not the frequency

PM, could you reply to that one?

Speed = distance / time

so

wave speed = wavelength * frequency.

When a wave passes into a medium with a different speed it keeps oscillating at the same rate, but its wavelength changes to conform to that equation.

Does that help?

Actually…yes.

I wasn’t thinking it through.

As lamba = v/f then of course if the v changes the lambda will but not necessarily the frequency. Of course, anything that is plus/minus 10% of 50 Hz is not really worth talking about.

stomps off

:)

Blood engineers.

Bloody electrical enginers.

:)P

Michael V said:

sibeen said:

PM 2Ring said:

Speed = distance / time

so

wave speed = wavelength * frequency.

When a wave passes into a medium with a different speed it keeps oscillating at the same rate, but its wavelength changes to conform to that equation.

Does that help?

Actually…yes.

I wasn’t thinking it through.

As lamba = v/f then of course if the v changes the lambda will but not necessarily the frequency. Of course, anything that is plus/minus 10% of 50 Hz is not really worth talking about.

stomps off

:)

Blood engineers.

Bloody electrical enginers.

:)P

I must admit though, MV, it does show, or at least to me, how set you can become in your thinking.

Then again, I am getting on a bit :)

If the frequency changed but the wavelength remained constant, it’d be a PITA trying to build radio receivers & transmitters. :)

sibeen said:

Michael V said:

sibeen said:

Actually…yes.

I wasn’t thinking it through.

As lamba = v/f then of course if the v changes the lambda will but not necessarily the frequency. Of course, anything that is plus/minus 10% of 50 Hz is not really worth talking about.

stomps off

:)

Blood engineers.

Bloody electrical enginers.

:)P

I must admit though, MV, it does show, or at least to me, how set you can become in your thinking.

Then again, I am getting on a bit :)

That’s the whole point of having a drink, isn’t it? So you don’t notice either thing.

Michael V said:

That’s the whole point of having a drink, isn’t it? So you don’t notice either thing.

I know nuthing!

< / schultz .

sibeen said:

Michael V said:

That’s the whole point of having a drink, isn’t it? So you don’t notice either thing.

I know nuthing!

< / schultz .

:)

Job done… :)