[Gerben42]

Quote

The relativistic mass of light is very real - it can be seen when the sight-line to a star is very close to that of the Sun and it looks as if the star has moved away from its normal position - what happens is an optimal illusion caused by the light from the start being bent by the gravity field of the Sun. Another example is when sunlight pushes small objects such as spaceships and comets' tails away, something that can be explained by the light's momentum being transfered to the object. A third example is gamma decay where the emitting atoms suffer a mass loss which can only be accounted for if the gamma ray took some of the mass with it.

Sorry, must correct you there. Photons do not have mass (translation: they do not couple with gravity, i.e. no matter how many photons you have, the gravitational potential won't change) but they do have momentum.

For a non-relativistic particle momentum p = m_0 v (rest mass times velocity), but the relativistic equation is:

p = m_0 * v / sqrt(1 - v²/c²), which of course leads to zero divided by zero for photons (m = 0 and v = c).

To explain the bending of light in a strong gravity field, you have to calculate the straight path in the curved space caused by the mass at the center. As predicted by Einstein, this bending is twice as large as what you'd expect if you would treat the photons as Newtonian particles that feel gravity. This effect was observed during a solar eclipse a few years after Einstein published his theory.

[luke warm]

so gerben, from a practical standpoint that means light never loses momentum but is affected by how gravity affects the space through which it (light) travels?

[Gerben42]

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so gerben, from a practical standpoint that means light never loses momentum but is affected by how gravity affects the space through which it (light) travels?

Yes, it follows the direction of the possibly curved space and retains it never-changing speed.

On the other hand there is the effect that clocks run faster at the bottom of a gravity well, so light escaping from the surface of a heavy object to "far away" will have a longer wavelength for the observer "far away" than it had for the observer on the surface.

Quote

ok, i'm muddling along i think... i guess, given the very small child understanding i have of this, the thought of light mass (of any kind, relativistic or otherwise) makes me wonder why C should be a constant

It might be or might not be, it's just that any theory must be able to predict what we observe, and what we observe is a constant light speed.

[gwnn]

in a semi hijacking move, I'd like to ask someone who understands GR and QM better than I why everyone is searching for the gravitons when the graviton model couldn't explain the bending of light.

[kenrexford]

I feel like such a light weight.

[blackshoe]

gwnn, on Jun 8 2008, 07:00 PM, said:

in a semi hijacking move, I'd like to ask someone who understands GR and QM better than I why everyone is searching for the gravitons when the graviton model couldn't explain the bending of light.

Because gravitons are likely to be necessary to the development of a unified field theory.

[gwnn]

blackshoe, on Jun 9 2008, 06:57 AM, said:

gwnn, on Jun 8 2008, 07:00 PM, said:

in a semi hijacking move, I'd like to ask someone who understands GR and QM better than I why everyone is searching for the gravitons when the graviton model couldn't explain the bending of light.

Because gravitons are likely to be necessary to the development of a unified field theory.

so you're saying the unified theory will say "light doesn't bend" ?

[blackshoe]

No. Why would you think that?

[mikeh]

luke warm, on Jun 8 2008, 08:11 AM, said:

ok, i'm muddling along i think... i guess, given the very small child understanding i have of this, the thought of light mass (of any kind, relativistic or otherwise) makes me wonder why C should be a constant

Welcome to the wonderful (and I mean that literally) world of scientific thinking, LW

We have had, and will no doubt continue to have, our differences in world view, but I suspect that these differences may diminish if this thread reflects an interest in understanding the model of the universe as currently postulated... and the ongoing efforts to improve that model.

FWIW, while the concepts surrounding light and phenomena such as gravitational lensing and black holes are fascinating, the real mind-blower of all that I have read about light is the 'twin slit experiment'.

To crudely, and perhaps inaccurately, summarize:

We have a light source that we can make emit only one photon at a time and we aim the photon at a barrier in which we have two slits. We observe the pattern that these photons make on a surface beyond the barrier. We note that we see a pattern suggesting that the photon, which is a single, indivisible 'thing', appears to be going through BOTH slits simultaneously! Somehow the photon seems to divide and then recombine. It is acting as if it were a wave.

This is weird, but add a detector adjacent to each slit... so that we can 'see' the photon as it goes through the slits. Mind, there is otherwise NO difference to the experimental setup.

Now, the photon goes through only ONE slit, and the pattern on the surface is different than the one when we are not observing the slits! It is acting as if it were a particle.

This is part of the wonder of the world revealed by the scientific method.

Maybe there is some quantum scientist who can intuitively visualize these things, but my suspicion is that this type of phenomenum, which takes place on a scale that our senses did not evolve to be able to observe directly, is likely beyond the capacity of our meat brains to ever fully comprehend, on an intuitive 'oh, yes, I get this' basis.

[helene_t]

mikeh, on Jun 9 2008, 07:54 PM, said:

This is weird, but add a detector adjacent to each slit... so that we can 'see' the photon as it goes through the slits. Mind, there is otherwise NO difference to the experimental setup.

Now, the photon goes through only ONE slit, and the pattern on the surface is different than the one when we are not observing the slits! It is acting as if it were a particle.

Yes, this is quite difficult to comprehend. I know a few people who claim that they do understand it, though. A few times I have learned to understand phenomena which I at first found similarly incomprensive - as a child I didn't understand Newton's laws, and later I didn't understand functions with discontinous derivatives.

I can almost understand relativity so I am sure it is possible for someone just slightly smarter and/or more devoted to the subject than I am to understand it fully.

I think it is possible to understand quantum mechanics, too. Although I don't understand it at all, I can see the explanations of it is written in a "language" similar to that used to explain other parts of physics. I think if you come to understand it 100% from an analytical point of view, you can train yourself to grasp it intuitively by forcing yourself to think of things in terms of quantum theory. Because that is how I learned to understand classical mechanics. Surely, classical mechanics is less foreign to our innate intuition than quantum theory, but it is only a matter of degree. Some classical phenomena are quite counter-intuitive too, and yet it is possible to learn to understand them intuitively.

[Al_U_Card]

Is a terry-cloth towel only 2 dimensional? Does its thickness count? And what about the little loops? Each one has dimensions that are "invisible" to the eye with insufficient definitive power.

QP and its mathematical theory are the building blocks for our reality. How we "perceive" this reality depends on our perspective and the resolution of our defining observations. It may sound philosophical, because for all intents and purposes it is. Is the world an illusion? Depends on your perspective, intent, awareness and the ability to discern that which occupies your attention.

[luke warm]

Al_U_Card, on Jun 9 2008, 03:58 PM, said:

Is a terry-cloth towel only 2 dimensional? Does its thickness count? And what about the little loops? Each one has dimensions that are "invisible" to the eye with insufficient definitive power.

QP and its mathematical theory are the building blocks for our reality. How we "perceive" this reality depends on our perspective and the resolution of our defining observations. It may sound philosophical, because for all intents and purposes it is. Is the world an illusion? Depends on your perspective, intent, awareness and the ability to discern that which occupies your attention.

wow... and just think, all of this (more or less) order came from disorder

[Gerben42]

Quote

QP and its mathematical theory are the building blocks for our reality.

No. Quantum Physics is a mathematical construct that is used to predict the behaviour of the universe in different situations. It has predictive power, but it is in a way "the best we could come up with".

In a sense we are at the same stage as 100 years ago, when Physics was basically a construct of classical mechanics and electromagnetism. The first demanded that the speed of light is variable, the second that it is constant.

Currently we are in a similar situation where we have two theories, both of which are obviously not "the last word" on anything, but predict very well for the problems in their own validity range.

Both Quantum and Relativity are "the best we could come up with" constructs that predict the behavior of the universe, but they are not the building blocks of our reality.

[Al_U_Card]

luke warm, on Jun 9 2008, 05:08 PM, said:

Al_U_Card, on Jun 9 2008, 03:58 PM, said:

Is a terry-cloth towel only 2 dimensional?  Does its thickness count?  And what about the little loops? Each one has dimensions that are "invisible" to the eye with insufficient definitive power.

QP and its mathematical theory are the building blocks for our reality.  How we "perceive" this reality depends on our perspective and the resolution of our defining observations.  It may sound philosophical, because for all intents and purposes it is.  Is the world an illusion?  Depends on your perspective, intent, awareness and the ability to discern that which occupies your attention.

wow... and just think, all of this (more or less) order came from disorder

Which counterbalances the greater tendency for order to become disorder....so reverse entropy proves the existence of...

[Al_U_Card]

Gerben42, on Jun 9 2008, 05:11 PM, said:

Quote

QP and its mathematical theory are the building blocks for our reality.

No. Quantum Physics is a mathematical construct that is used to predict the behaviour of the universe in different situations. It has predictive power, but it is in a way "the best we could come up with".

In a sense we are at the same stage as 100 years ago, when Physics was basically a construct of classical mechanics and electromagnetism. The first demanded that the speed of light is variable, the second that it is constant.

Currently we are in a similar situation where we have two theories, both of which are obviously not "the last word" on anything, but predict very well for the problems in their own validity range.

Both Quantum and Relativity are "the best we could come up with" constructs that predict the behavior of the universe, but they are not the building blocks of our reality.

Hi Gerben

If you use them as such then that is what they are. One of our better capacities.

When the blocks get better we can adapt to using them to improve our understanding. Pretty much sums up what has been going on for quite some time now...

[luke warm]

Al_U_Card, on Jun 9 2008, 07:24 PM, said:

luke warm, on Jun 9 2008, 05:08 PM, said:

Al_U_Card, on Jun 9 2008, 03:58 PM, said:

Is a terry-cloth towel only 2 dimensional?  Does its thickness count?  And what about the little loops? Each one has dimensions that are "invisible" to the eye with insufficient definitive power.

QP and its mathematical theory are the building blocks for our reality.  How we "perceive" this reality depends on our perspective and the resolution of our defining observations.  It may sound philosophical, because for all intents and purposes it is.  Is the world an illusion?  Depends on your perspective, intent, awareness and the ability to discern that which occupies your attention.

wow... and just think, all of this (more or less) order came from disorder

Which counterbalances the greater tendency for order to become disorder....so reverse entropy proves the existence of...

hey, i'm just sayin'... btw, is there a tendency towards disorder? what is needed for order to occur from disorder?

[helene_t]

luke warm, on Jun 10 2008, 11:16 AM, said:

hey, i'm just sayin'... btw, is there a tendency towards disorder? what is needed for order to occur from disorder?

That disorder is created elsewhere to balance it. For example when a plant grows, the growing plant itself represents growing order but it is balanced by the fact that it uses relatively ordered ultraviolet light for its photosynthesis and returns the energy from the light in the form of relatively disordered infrared light.

[han]

I think Gerben's last post is very good and important for several reasons.

[Al_U_Card]

luke warm, on Jun 10 2008, 05:16 AM, said:

Al_U_Card, on Jun 9 2008, 07:24 PM, said:

luke warm, on Jun 9 2008, 05:08 PM, said:

Al_U_Card, on Jun 9 2008, 03:58 PM, said:

Is a terry-cloth towel only 2 dimensional?  Does its thickness count?  And what about the little loops? Each one has dimensions that are "invisible" to the eye with insufficient definitive power.

QP and its mathematical theory are the building blocks for our reality.   How we "perceive" this reality depends on our perspective and the resolution of our defining observations.  It may sound philosophical, because for all intents and purposes it is.  Is the world an illusion?  Depends on your perspective, intent, awareness and the ability to discern that which occupies your attention.

wow... and just think, all of this (more or less) order came from disorder

Which counterbalances the greater tendency for order to become disorder....so reverse entropy proves the existence of...

hey, i'm just sayin'... btw, is there a tendency towards disorder? what is needed for order to occur from disorder?

The divine spark, consciousness.

[luke warm]

helene_t, on Jun 10 2008, 05:29 AM, said:

luke warm, on Jun 10 2008, 11:16 AM, said:

hey, i'm just sayin'... btw, is there a tendency towards disorder? what is needed for order to occur from disorder?

That disorder is created elsewhere to balance it. For example when a plant grows, the growing plant itself represents growing order but it is balanced by the fact that it uses relatively ordered ultraviolet light for its photosynthesis and returns the energy from the light in the form of relatively disordered infrared light.

i guess i just don't understand it then... it's very hard to imagine the earth, after the BB, becoming "ordered" from its molten state