lightspeed question.

[wishingwell]

should light falling into a blackhole be accelerated due to gravity?

[Rich F]

Does light have mass?

E=mc(squared), so yes, it does!

(But if you took a photon, the amount of energy it has is pretty minute, so when you divide that by the "c2" term, the equivalent mass you get is even more minute... :-|

[Rich F]

That's what Albert would say, yes...! :s5

[lee]

QUOTE: In post 442891, Rich F said:
That's what Albert would say, yes...! :s5


You aren't Richard Franklin by any chance are you?

The first argument I ever had on-line was with him.

Way back in Lineone days.

[Fork Me]

QUOTE: In post 442884, Maximus Desimus Meridius said:
apparently the speed of light is constant & doesn't change its velocity, only its direction, due to mass....

Now if I was gonna be picky....

.....aaaaw, what the Hell, let's do it anyway!

When something changes direction it ALWAYS changes velocity, velocity is a vector quantity and therefore directional. Something travelling at constant SPEED in a circle is constantly changing VELOCITY.


... Which for me, begs the question ~ does light itself have mass ..?:s8... Now that's an interesting question:D


No, it doesn't, according to most physicists. Note the use of the word "most"!.

Photons are considered to have no mass at all, but no-one has proved that yet. (although I seem to recall a lower limit being set a while back and a quick google has shown that it has been experimentally proven than a photon has a mass of less than 10^-51 grams (for comparisom, the electron, previously thought to be massless has a mass of approx 9x10^-28 grams, or 900 billion trillion times the lower limit mentioned!).

Photons are known to have momentum but every schoolboy physicist is taught that momentum=mass x velocity, so how could they have momentum without mass? Well, they still could, mom=mv only works at speeds much slower than light speed. There is another part of the equation which adds so little at sub light speeds as to be irrelevant, but photons travel at the speed of light, so it IS relevent.

Fork Me

[Rich F]

You aren't Richard Franklin by any chance are you?


No: actually, "Rich F. stands for "Rich F**k", an sort-of up-to-date summary of the NT parable about the "rich young man" who wanted to be a disciple but couldn't give up the good life!

But if light has mass as I surmise, then surely the speed could change,...

Take care to distinguish between "rest mass" and inertial / gravitational mass. Light has one but not 'tother (as Fork Me is - sort of - saying, above). See here (http://musr.physics.ubc.ca/~jess/p200/emc2/node11.html) for the maths!

And remember to avoid mixing Newtonian ("schoolboy") mechanics with the relativistic version!

;-)

[Rich F]

Actually, I thought we were talking acceleration, not velocity!

[Fork Me]

QUOTE: In post 442908, Tantric Tart said:
So, that being the case, the whole universe is out of control, should it be constantly changing.

Or, to put it another way...all the planets in the known universe are incapable of remaining in sync?

I don't think so.

Why do you say that?

My post didn't even suggest it. Although of course, the Universe IS constantly changing.

Fork Me

[Fork Me]

QUOTE: In post 442909, Rich F said:
Actually, I thought we were talking acceleration, not velocity!

My correction sprang from Max's use of the word velocity in the second post in this thread, however, as I was talking about a change in velocity, that IS acceleration.

Acceleration is also a vector quantity and is thus directional as well.

Acceleration is defined as a change of velocity, not a change of speed.

Fork Me

[Rich F]

Thanks, Fork Me - I actually didn't quite want to go there, cos it wasn't quite what MMD had in mind! But what you say is true enough!

(Does that answer wishingwell's original question, then - as yes?)

Hi Max: yup, your question above is the classic, innit!

To which the standard reply is: ah, but you're forgetting the Lorentz transformation (http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/veltran.html) (CARE! Calculus approaching!), which leads to the Einstein velocity relationship (http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html). (No calculus there, you'll be glad to see - just the formula you need)!

s:24

[Fork Me]

QUOTE: In post 443089, Maximus Desimus Meridius said:

If two cars are approaching each other, each travelling at 80mph, when they collide, the combined relative velocity would be 160mph, a simple case of 1+1=2.

<SNIPped for clarity, but read>



The problem is that your example uses Newtonian mechanics. Newtonian mechanics only works at speeds way below the speed of light.

Einstein, with relativity, found that Newtonian mechanics are only an estimation, an estimation good enough for everyday life, but at light speeds and near light speeds things get a lot more complicated.

You used light as an example, but it works with matter as well.

Imagine that a gun fires a bullet at a speed of 100ms-1.

Concorde cruised at 1350mph, which is approximately 600ms-1.

Now if a terrorist hi-jacked Concorde and fired a bullet in the dorection Concorde was travelling, the bullets actual speed would be (600+100) 700ms-1.

Simple Newtonian physics.

Now imagine we had invented a jet that travelled just 50ms-1 slower than the speed of light. Surely the bullet would travel 50ms-1 faster than light????

But of course, it wouldn't, it couldn't, Einstein said so! Again, the problem is that we are over simplifying, Newtonian physics just don't work that close to light speed.

Fork Me

[Rich F]

Whether abstract, profound, or just mystic,
Or boring, or somewhat simplistic,
A theory must lead
To results that we need
In limits, nonrelativistic.

[Fork Me]

QUOTE: In post 443197, Maximus Desimus Meridius said:
Odd,... you snipping me...

No offence intended, the SNIP was merely to make the thread easier to follow.

There's nothing worse than having to constantly scroll though the same text over and over again because of lazy quoting.


The Newtonian bit you quoted was the superfluous part of my example as we all know this...

And the snipped out bit was the point of Einsteins theory which you regurgitated in a different manner... Mine was simpler & text book...


No, the bit I SNIPped was an attempt to use Newton to explain the behaviour of light. It doesn't work. It has been experimentally proven not to work.



but of course the bullet doesn't travel faster than light..... Apparently it cannot according to @ssole Albert, though anything we now say to the contrary is pure conjecture...:rofl:, innt it:s8 :rofl:


Why do you call Einstein an @sshole?

He had one of the greatest minds ever, and many of his theories have been demonstrated experimentally since his death.

Newton (who, despite having a brilliant mind and being one of the greatest mathemeticians/scientists ever to have lived, WAS an @sshole in life!) explained things to an accuracy that worked for observable reality. However, his explanations DON'T work at the extremes.

Relativity works better at the extremes but not perfectly.

Quantum mechanics takes thing yet another step furtherand many have tried and failed (so far) to marry the two together to give a working universal theory.

The BIG problem with both relativity and quantum mechanics is much of it is counter intuitive, the math needed to prove it is beyond the vast majority of the population (and I include myself among that vast majority) and virtually all of it is difficult, if not impossible to prove experimentally.

However, they are the best we've got, and they seem to work, certainly many predictions made using them have been shown to be correct.

Fork Me

[wishingwell]

HAs anybody tried altering the maths we use to apply to the quantum world.after all i presume the quantum world has been here as long as the normal world,and coudnt the reason it appears strange is that our maths are faulty.or that the wrong type of maths is being applied.

[Rich F]

Schrodinger did it, back in 1933 (or so), ww !

We - or rather, the mathemagicians! - use somewhat updated and more elegant maths methods these days, but essentially we get the same result: if you stick to relativity, you're fine - LUVly results, bang-on predictions, experimental matching practically guaranteed.

If you do quantum stuff, same thing.

If you try to mix 'n match, though (which you have to do for near the start of the unverse, when things were quantum sized) - POW! ker-SPLAT! OOMPH! UUrrghhh....

In short, disaster.

Which is why lots of them now play with the very very very hard maths of superstring theory.

[Fork Me]

QUOTE: In post 443293, wishingwell said:
HAs anybody tried altering the maths we use to apply to the quantum world.after all i presume the quantum world has been here as long as the normal world,and coudnt the reason it appears strange is that our maths are faulty.or that the wrong type of maths is being applied.

Several people have tried. :)

Fork Me

[Rabbit]

QUOTE: In post 443089, Maximus Desimus Meridius said:
True.... a lapse on my part, so I stand corrected


If two cars are approaching each other, each travelling at 80mph, when they collide, the combined relative velocity would be 160mph, a simple case of 1+1=2.
Common sense tells us that if a source of light is travelling towards us at say half the speed of light (0.5c) & is emitting light (velocity = c), then the light which arrivesshould be approaching at one & a half times the speed of light (1.5c). The theory however states quite clearly that this is not so; the measured velocity is just "c"; 1+0.5=1...... apparently.:rolleyes:

But the velocities are not added. If a car is approaching you at high speed, and an identical car is moving away from you at the same speed, they will each sound different to you, but the sound waves reaching your ears are all travelling at the same speed. What's happening is the wavelengths are shifted; the distance between wave crests is either contracted or expanded depending on whether the source of the sound is approaching or receding (see attached picture)

This "Doppler Effect" also applies to light waves, and the wavelength shift is given by the formula:
(l1 - l2) / l1 = v/c
where l1 is the actual wavelength,
l2 is the observed wavelength
v is the relative velocity between source and observer, and
c is the speed of light.1


In the case of the car, as it goes past you, the pitch drops.
With light, an approaching source gives a Doppler shift2 towards the blue end of the spectrum, and light from a receding source is red-shifted.
As the diagram shows, the wave front is circular, meaning the waves are travelling at the same speed in every direction, regardless of the speed of the source, assuming the observer is not moving relative to the medium.

Rab

1. This formula is an approximation that only works well at "normal" speeds. For sources moving at relativistic speeds, the formula must be modified to be consistent with the Lorentz transformations, but the upshot is, it's the lengths of the waves that change, not their speed.
2. For the pedantic, when applied to light, the red/blue shift is known as the Doppler-Fizeau effect.

[Memnoch]

QUOTE: In post 442884, Maximus Desimus Meridius said:
apparently the speed of light is constant & doesn't change its velocity, only its direction, due to mass....

... Which for me, begs the question ~ does light itself have mass ..?:s8... Now that's an interesting question:D
Not if E=Mc² is correct: According to that, if light had mass it would need infinite energy to attain velocity c.

M

[wishingwell]

QUOTE: In post 443808, Memnoch said:
Not if E=Mc² is correct: According to that, if light had mass it would need infinite energy to attain velocity c.

M so what is the gravity actually acting on,as the light is pulled down into said hole.


(could it be an illusion,the medium the light is travelling in is maybe subject to gravitational effect,and a type of internal refraction could be trapping the light,so the light itself not actually,or directly being subject directly to gravity)

[Olespice]

QUOTE: In post 445146, wishingwell said:
so what is the gravity actually acting on,as the light is pulled down into said hole.


(could it be an illusion,the medium the light is travelling in is maybe subject to gravitational effect,and a type of internal refraction could be trapping the light,so the light itself not actually,or directly being subject directly to gravity)


Oh. woe is me. I read all the way through the comments and get back to you again, W, when you ask a question that supposes an action, that of the light going into the black hole....

Could not light be the only anti-gravity force we know? After all, it doesn't obey so far as we know, the law of physics as other known objects or matter.

Force? Can it not be a different force from other forces we can measure? The point about it not travelling at a speed plus the speed of the object from which it is emitted; could it not be possible that it leaves its source so fast that it is equivelant to commencing from a stationary source? What about the light source which, allowed to arrive at the surface of a finely balanced spindle and 'sail' in a vacuum, having a darkened surface one side and a shiny light reflective surface the other, then turns the balanced spindle holding that sail? We must have all seen it. Also, the space sail recently suggested for space travel, based on the same principle?

Olespice.

[wishingwell]

QUOTE: In post 445165, olespice said:
Oh. woe is me. I read all the way through the comments and get back to you again, W, when you ask a question that supposes an action, that of the light going into the black hole....

Could not light be the only anti-gravity force we know? After all, it doesn't obey so far as we know, the law of physics as other known objects or matter.

Force? Can it not be a different force from other forces we can measure? The point about it not travelling at a speed plus the speed of the object from which it is emitted; could it not be possible that it leaves its source so fast that it is equivelant to commencing from a stationary source? What about the light source which, allowed to arrive at the surface of a finely balanced spindle and 'sail' in a vacuum, having a darkened surface one side and a shiny light reflective surface the other, then turns the balanced spindle holding that sail? We must have all seen it. Also, the space sail recently suggested for space travel, based on the same principle?

Olespice. yes ,i forget the name of the device you describe showing how light has a pushing aspect,are you saying that you think light is attracted because it follows that opposites attract,as light is pushed away from the mass of the sun,wouldnt it be forced away from the black hole.

[wishingwell]

QUOTE: In post 445165, olespice said:
Oh. woe is me. I read all the way through the comments and get back to you again, W, when you ask a question that supposes an action, that of the light going into the black hole....

Could not light be the only anti-gravity force we know? After all, it doesn't obey so far as we know, the law of physics as other known objects or matter.

Force? Can it not be a different force from other forces we can measure? The point about it not travelling at a speed plus the speed of the object from which it is emitted; could it not be possible that it leaves its source so fast that it is equivelant to commencing from a stationary source? What about the light source which, allowed to arrive at the surface of a finely balanced spindle and 'sail' in a vacuum, having a darkened surface one side and a shiny light reflective surface the other, then turns the balanced spindle holding that sail? We must have all seen it. Also, the space sail recently suggested for space travel, based on the same principle?your observations lead me back to what i had to say about light and gravity on another thread ,that light is a more realistic force and instigater than gravity is.(its not me who supposes that light is pulled in due to gravity,its mainstream science view i have said it could be an illusion.)

[Memnoch]

QUOTE: In post 445146, wishingwell said:
so what is the gravity actually acting on,as the light is pulled down into said hole.


(could it be an illusion,the medium the light is travelling in is maybe subject to gravitational effect,and a type of internal refraction could be trapping the light,so the light itself not actually,or directly being subject directly to gravity)
Not the medium but space itself, according to Einstein. In relativity theory, space is curved in 4 dimensions, and the paths of objects falling freely in a gravitational field look curved from our perspective but are actually straight lines through curved "spacetime".

You seem to be describing an optical effect known as "Total Internal Reflection." I don't think a gravity field can produce that effect because that would imply a gravitationally closed space, which is by definition a black hole, and anything inside the event horizon of a black hole must eventually fall to the center.

M

[wishingwell]

QUOTE: In post 445171, Memnoch said:
Not the medium but space itself, according to Einstein. In relativity theory, space is curved in 4 dimensions, and the paths of objects falling freely in a gravitational field look curved from our perspective but are actually straight lines through curved "spacetime".

[quote]You seem to be describing an optical effect known as "Total Internal Reflection." I don't think a gravity field can produce that effect because that would imply a gravitationally closed space, which is by definition a black hole, and anything inside the event horizon of a black hole must eventually fall to the center.

M i was thinking here of a physics experiment where a lidded glass jar full of water ,had its sides blackened out srapped to a torch,a hole is poked in the lid ,in a darkend room,and when the water spurts out to the ground the light is carried within the water,thus it could appear in some circumstances that gravity is acting directly on or bending the light.

[wishingwell]

QUOTE: In post 445171, Memnoch said:
Not the medium but space itself, according to Einstein. In relativity theory, space is curved in 4 dimensions, and the paths of objects falling freely in a gravitational field look curved from our perspective but are actually straight lines through curved "spacetime".

but wouldnt this also apply to planets orbiting the sun.i have heard that they are travelling in straight lines,but they do have circular,or curved orbits.

[Memnoch]

QUOTE: In post 445175, wishingwell said:
i was thinking here of a physics experiment where a lidded glass jar full of water ,had its sides blackened out srapped to a torch,a hole is poked in the lid ,in a darkend room,and when the water spurts out to the ground the light is carried within the water,thus it could appear in some circumstances that gravity is acting directly on or bending the light.
Water refracts and reflects light, and I'm pretty sure those optical properties alone would account for any effect witnessed. The gravity field in this locality wouldn't have enough of an effect on light that you could detect it with the naked eye.

M

[wishingwell]

QUOTE: In post 445183, Memnoch said:
Water refracts and reflects light, and I'm pretty sure those optical properties alone would account for any effect witnessed. The gravity field in this locality wouldn't have enough of an effect on light that you could detect it with the naked eye.

M also in respect to planets atmosphere and heat radiation,and stars heat radiation this can have a bending effect on light passing them.similar to mirage effects.