Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: JohnDuffield on 02/02/2015 22:36:52
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You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now we make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down.
So why doesn't the light get out?
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You're standing on a gedanken planet holding a laser pointer straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now we make the planet denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive. The light still doesn't curve round, or slow down as it ascends, or fall down. We make the planet even denser and more massive, and take it to the limit such that it's a black hole. At no point did the light ever curve round, or slow down as it ascends, or fall down.
So why doesn't the light get out?
Discounting other possible limitations and or other physical details, the source of the light is falling toward the center at light speed. With the light source falling toward the center at light speed, would this freeze the beam at the event horizon or would it appear that the beam was traveling in the direction toward the singularity. I'm frankly not sure which is the case. This may or not be the answer you're seeking but it's the only one I can come up with.
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It's a strange question John. Are you assuming a atmosphere showing us the lights path inside that black hole? And then a observer able to follow that path up to some 'event horizon' to then 'curve' back to some center? It's a geodesic, that is formed by gravity. And it's pretty hard seeing the light 'move', you only see it 'interact'. Everything in SpaceTime (uniformly moving) follows geodesics, light is no exception. Our Earth does it too.
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Discounting other possible limitations and or other physical details, the source of the light is falling toward the center at light speed. With the light source falling toward the center at light speed, would this freeze the beam at the event horizon or would it appear that the beam was traveling in the direction toward the singularity. I'm frankly not sure which is the case. This may or not be the answer you're seeking but it's the only one I can come up with.
No, the light source isn't falling. And IMHO what's interesting about this question, is that most people can't give a satisfactory answer even though they feel they're knowledgeable about black holes.
It's a strange question John.
It's one of those naïve simple little questions that really makes you think. Or at least I hope it is.
Are you assuming a atmosphere showing us the lights path inside that black hole?
No, but we could sprinkle some dust around if that helps.
And then a observer able to follow that path up to some 'event horizon' to then 'curve' back to some center? It's a geodesic, that is formed by gravity. And it's pretty hard seeing the light 'move', you only see it 'interact'. Everything in SpaceTime (uniformly moving) follows geodesics, light is no exception. Our Earth does it too.
The point is that the vertical light beam doesn't curve round. It goes straight up. So why doesn't the light get out?
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No, the light source isn't falling.
If the light source isn't falling, then another explanation is; The beam is in a perpetual orbit around the black hole disallowing it's escape.
Another scenario would be that the intense gravitational force has slowed the passage of time to such a degree that the light hasn't had sufficient time to escape? With the passage of time at a virtual standstill within this gravity well, light would appear to be frozen in place to the outside observer. The state of affairs within the black hole would be vastly different for the fellow with the flash light however.
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If the light source isn't falling, then one other other explanation is; The beam is in a perpetual orbit around the black hole disallowing it's escape.
No. The beam starts off vertical, we increase the gedanken mass/density, and the beam stays vertical. It never strays from vertical. We don't see it curving a little when we're getting close to black-hole density.
Or could it be that the intense gravitational force has slowed the passage of time to such a degree that the light hasn't had sufficient time to escape? With the passage of time at a virtual standstill within this gravity well, light would appear to be frozen in place to the outside observer.
Now you're talking. Note though that "the passage of time" is a figure of speech. There is no actual time passing inside an optical clock, or inside any other clock. See this Einstein quote (http://einsteinpapers.press.princeton.edu/vol7-trans/156?highlightText=%22speed%20of%20light%22).
The state of affairs within the black hole would be vastly different for the fellow with the flash light however.
That's what people say. And it's another can of worms.
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Note though that "the passage of time" is a figure of speech. There is no actual time passing inside an optical clock, or inside any other clock.
The subject of "Time" is a very debatable topic. Being a conscious abstraction we personally relate to change, time is of course difficult to quantify. Only when we have uniform metrics agreeable to every observer does time take on a meaningful quality. Even then, time is still only a personalized conscious experience.
"Time is different everywhere because "change" is what makes the difference.".............................Ethos
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Time is the key. I don't know if you've ever seen this (http://www.amazon.co.uk/World-without-Time-Forgotten-Einstein/dp/0465092942). But once you appreciate that a clock "clocks up" some kind of regular cyclical motion rather than the literal flow of time, IMHO it's rather liberating. You then appreciate that when an optical clock goes slower when it's slower, it's because light goes slower. Hence you appreciate what Einstein was saying in the second paragraph here (http://einsteinpapers.press.princeton.edu/vol7-trans/156?highlightText=%22speed%20of%20light%22):
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D54160.0%3Battach%3D19455%3Bimage&hash=996897d8b077cbd11f692c13ad526541)
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Time is the key.
Might I have your consent to respectfully rephrase that line with the following?........... "Change is the key"
I don't know if you've ever seen this (http://www.amazon.co.uk/World-without-Time-Forgotten-Einstein/dp/0465092942).
Haven't read the book but I agree that the use of the word "time" usually only clouds the issues about reality.
I'll withhold further opinions about how I understand "time" so as not to guide this thread off topic. Just allow me to say three things about time and I'll shut up about it.
1. The past is not a point in time, it was a place which has changed to our present location.
2. The future is not a point in time, it is a location which we have yet to visit.
3. And the present will continuously morph into new realities leaving us with only the memories of it. The present is lost before it's realized.
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Might I have your consent to respectfully rephrase that line with the following?........... "Change is the key"
Yep. And my blessing.
Haven't read the book but I agree that the use of the word "time" usually only clouds the issues about reality.
I'll withhold further opinions about how I understand "time" so as not to guide this thread off topic. Just allow me to say three things about time and I'll shut up about it.
1. The past is not a point in time, it was a place which has changed to our present location.
2. The future is not a point in time, it is a location which we have yet to visit.
3. And the present will continuously morph into new realities leaving us with only the memories of it. The present is lost before it's realized.
All good stuff. OK, to get back on topic, get a load of this:
Optical clocks go slower when they're lower, because light goes slower when its lower. Check out the coordinate speed of light. Einstein didn't call it that, so I won't. I'll just call it the speed of light. Anyway, in the normal course of events, when you're standing on a planet rather than a black hole...
the vertical light beam speeds up
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Without subjecting a photon to traveling through some super cooled medium or by other means you will never be able to detect a change in the speed of light. It will change between frames where the properties of the fields in those frames differ from each other. However EVERYTHING changes proportionally with the photon. If a photon slows down by 0.01% then an electron slows down by 0.01% and a proton and a neutron. That is why, in a vacuum to remove air resistence, dropping an elephant and a mouse from the same height they will both hit the ground at the same time. Oh my god john, I am so sorry, I mentioned the T word.
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However EVERYTHING changes proportionally with the photon. If a photon slows down by 0.01% then an electron slows down by 0.01% and a proton and a neutron.
You got it. Everything slows down, including you and your clocks, so you can't tell that the light has slowed down. We call it gravitational time dilation, but at no juncture can we ever see this thing called time which is said to slow down.
Oh my god john, I am so sorry, I mentioned the T word.
We should play a little game where we talk physics, but aren't allowed to say "time". I tell you, it isn't easy.
Oh, and Ethos, cross my heart and hope to die, but when the vertical light beam is pointed down rather than up, it slows down. Is that counterintuitive or what? Nowhere will you ever read that in any textbook. You will read about the coordinate speed of light varying with gravitational potential, but the true ramifications of that don't get mentioned. Not that I'm aware of anyway. Anyway, this is how Professor Tom Moore answered the question:
"...As the planet's mass approaches the black hole limit, the signal emitted from the surface will seem to move more and more slowly away from the surface (and will also be seen to be increasingly red-shifted as observed from infinity). When the surface of the planet coincides with the black hole's event horizon, the signal will stop moving outward from the surface (and the redshift observed at infinity will go to infinity). So light no longer escapes..."
The light doesn't get out because it's stopped.
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Wow I got it. Do I get a medal? Sorry about the sarcasm John but do you really think I have just started thinking about this stuff? I have spent 25 years thinking about it. It is only now that I have had the time to get serious about following it up.
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Wow I got it. Do I get a medal? Sorry about the sarcasm John but do you really think I have just started thinking about this stuff? I have spent 25 years thinking about it. It is only now that I have had the time to get serious about following it up.
Don't feel lonesome there Jeff, I'm 72 years young and have been interested in Black Holes for the majority of my adult years. I remember discussing this phenomenon with a friend of mine 50 years ago. I suggested to him then that I felt that a Black Hole was lurking at the center of just about every galaxy in the universe. He exclaimed to me that he didn't believe in Black Holes and that was the end of our conversation. Needless to say, whether they are called Black Holes or described as some other freak of nature, research has now proven with little opposition that such a scenario presently exists. I haven't met up with this fellow for many years but if I ever see him again, there's going to be an "I told you so" in our conversation.
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Your problem is twofold John. One is your presumption of watching that 'light path', finding it to go 'straight'. The other is the idea of a geodesic being something that doesn't exist. It does, that's what all uniform motion is about. And geodesics are a result of the idea on no 'resistance' and a result of gravity interacting with 'mass and energy' or momentum if you like. A black hole is to its definition a place where noting can pass the event horizon due to gravity. So assuming this to be non-existent you also redefine a black hole to 'something else', what it should be I don't know? You also put into question the way Einstein proved GR https://en.wikipedia.org/wiki/Tests_of_general_relativity as all of those is about the same thing you question? Namely how light 'curves' following those 'geodesics'.
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I haven't got a problem, yor_on. The vertical or radial light beam goes straight. It just doesn't curve. It's like the "geodesic" that passes between two stars. It's a straight line. There's still a Shapiro delay, but there is no curvature of the light beam. And the Shapiro delay (http://en.wikipedia.org/wiki/Shapiro_delay) is there because "the speed of a light wave depends on the strength of the gravitational potential along its path". I don't redefine a black hole to be something else. It's small, it's dense, it's black, and light doesn't get out. Nor do I put into question the way Einstein proved GR. I'm referring to Einstein here. Light doesn't curve because it follows those geodesics. Einstein never said that. What he said is light curves because the speed of light varies with position. See for example this quote (http://einsteinpapers.press.princeton.edu/vol6-trans/340?highlightText=%22curvature%20of%20rays%22). Note though that the translation employs the word velocity rather than speed, which is a pity. However you can tell it should be speed because he refers to one of the two fundamental assumptions in the special theory of relativity.
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Wow I got it. Do I get a medal? Sorry about the sarcasm John but do you really think I have just started thinking about this stuff? I have spent 25 years thinking about it. It is only now that I have had the time to get serious about following it up.
Sorry Jeffrey. But this is so simple, and yet so few people know about it. Try asking the question somewhere else, and you'll see what I mean.
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Let me see if I get you straight? You define gravity to a varying of the speed of light, as defined from a 'container model' in where we all will agree to different 'time densities' due to this variation? Or would you separate time from gravity, how? And then we come to uniform motion, how do you define the 'densities' there?
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Maybe it gets knocked back down by other particles (photons)?
Is there something one may call squeezed light?
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As if photons interacted with other photons?
Now you added something to Johns idea :)
The only definition I've seen there is the idea of two 'photon interactions'
"From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple. This fermion pair can be leptons or quarks. Thus, two-photon physics experiments can be used as ways to study the photon structure, or what is "inside" the photon."
that's more or less about a regime where we had a 'hot' constricted universe. It's what I would call a 'container model'
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As if photons interacted with other photons?
Now you added something to Johns idea :)
The only definition I've seen there is the idea of two 'photon interactions'
"From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple. This fermion pair can be leptons or quarks. Thus, two-photon physics experiments can be used as ways to study the photon structure, or what is "inside" the photon."
that's more or less about a regime where we had a 'hot' constricted universe. It's what I would call a 'container model'
When speaking of Radiation pressure photons gently push matter even though it’s said photons have no mass, like for solar sails and in optical tweezers and the Casimir effect. If this matter was leptons or quarks, would it be wrong to say that photons may interact with each other, with some extra energy from the quantum vacuum? Maybe that is what happens if they hit each other on a sweet spot? It’s an elastic or inelastic impulse (“+vacuum energy”) which set particles out of path. Is it possible that the probably energetic dense field where this is happening somehow has the characteristics of setting all particles trying to get out from the black hole pushed back?
Just two humble questions: Since light is bent by gravity, do we need to redefine the definition of mass? What may not fluctuate into something else within the boundaries of the uncertainty principal if Big bang was such a fluctuation?
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The law of universal gravitation
Even light, the estimate cannot escape this theory.
This is the most unreliable but possible conclusion that I can think of.
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I´ve been told to not see universe intuitively since universe is not intuitive. Others may have been told just to continue the calculations without thinking intuitively. Is our force of intuition inherited from universe, or is it the other way around? Maybe we should stop counting, at least for a moment or two, and start to think, intuitively? Maybe we will find if we seek? Maybe there is something north of the North Pole after all? Maybe God is somewhat of a gambler? We are. Have we created God?
Was it an infinitely small volume that set of Big bang trough a quantum fluctuation? Does the volume of space itself expand? Is this volume expanding into nothing? Do we need gravitons, antigravitons and/or gravitational waves when we try to explain forces of universe, or do the Standard model give us what we need? Maybe we should use our intuition when we answer those questions, or is there a widening abyss between the two camps, QM and Relativity theory, that makes it impossible for individuals to think out of the box without risking everything, as easy targets of sharks? What are researchers that partly supported Le Sage's theory of gravitation in the 20th century doing today?
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Let me see if I get you straight? You define gravity to a varying of the speed of light, as defined from a 'container model' in where we all will agree to different 'time densities' due to this variation? Or would you separate time from gravity, how? And then we come to uniform motion, how do you define the 'densities' there?
I'm sorry yor_on, I'm not clear what you mean here. Einstein said light curves because the speed of light varies with position. That's simple enough. Then think of the wave nature of matter, and think of an electron as some kind of light-like wave in a closed path, then simplify it to a square path. The horizontals curve downwards and the electron falls down. And since only the horizontals curve downwards, light is affected twice as much as matter.
As if photons interacted with other photons? Now you added something to Johns idea :) The only definition I've seen there is the idea of two 'photon interactions'
"From quantum electrodynamics it can be found that photons cannot couple directly to each other, since they carry no charge, but they can interact through higher-order processes. A photon can, within the bounds of the uncertainty principle, fluctuate into a charged fermion–antifermion pair, to either of which the other photon can couple. This fermion pair can be leptons or quarks. Thus, two-photon physics experiments can be used as ways to study the photon structure, or what is "inside" the photon."
that's more or less about a regime where we had a 'hot' constricted universe. It's what I would call a 'container model'
That's wrong I'm afraid. Look carefully at what the article is saying. It's saying one 511keV photon somehow spontaneously "fluctuates" into a 511keV electron and a 511keV positron. And that if pair production doesn't occur, they somehow fluctuate back into one 511keV photon in defiance of conservation of momentum and conservation of energy. And that this photon somehow managed to keep on propagating at c! It's a fairy tale, and a tautology. Gamma-gamma pair production doesn't occur because pair production occurred, spontaneously, like worms from mud. It occurs because photons interact with photons.
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When speaking of Radiation pressure photons gently push matter even though it’s said photons have no mass, like for solar sails and in optical tweezers and the Casimir effect. If this matter was leptons or quarks, would it be wrong to say that photons may interact with each other, with some extra energy from the quantum vacuum? Maybe that is what happens if they hit each other on a sweet spot? It’s an elastic or inelastic impulse (“+vacuum energy”) which set particles out of path. Is it possible that the probably energetic dense field where this is happening somehow has the characteristics of setting all particles trying to get out from the black hole pushed back?
When you read the original material by Einstein, you can find answers to most of the questions. Like, the photon has no rest mass, but it does have an inertial mass.
Just two humble questions: Since light is bent by gravity, do we need to redefine the definition of mass?
No. The mass of a body is a measure of its energy-content. Trap a massless photon in a mirror-box, and it adds to the mass of that body.
What may not fluctuate into something else within the boundaries of the uncertainty principal if Big bang was such a fluctuation?
IMHO this "fluctuation" stuff is a non-answer pretending to be an answer.
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You're right John. I was thinking of that first radiation in a Big Bang, the one that's 'hidden', more or less.When it comes to the idea of spontaneous vacuum fluctuations though? "In quantum physics, a quantum fluctuation (or quantum vacuum fluctuation or vacuum fluctuation) is the temporary change in the amount of energy in a point in space,[1] as explained in Werner Heisenberg's uncertainty principle.
That means that conservation of energy can appear to be violated, but only for small values of t (time). This allows the creation of particle-antiparticle pairs of virtual particles. The effects of these particles are measurable, for example, in the effective charge of the electron, different from its "naked" charge."
In this case it has very little to do with 'photons interacting', other than it is about a pair production that returns inside some immeasurable amount of time. If it was measurable it would indeed be a violation. As for Claes, I see no wrong in using intuition :) As long as one find a way to defend it physically. If you instead of a 'propagating' 'field', just leave it be a 'field', locally defined, and then use 'c' as a 'ideal clock' losing its definition first at Planck scale, then you have something with a constant local 'beat'. That 'beat' won't change for anyone, no matter where one go . You can translate it into a 'life span', as locally measured. And that is what we do here too, (as in how it works), even though we could be seen as being 'at rest', with Earth.
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what I mean Claes, is that it then becomes 'rules' that define how this 'field' behave. Those 'rules' are all local, but also shared by us all, locally measuring. In their extension they then become the base for what we define as 'repeatable experiment', defining our sciences. When we do one we presume a local 'time keeping', being the same for us all, as well as we presume equivalent rulers etc. What we call constants, as 'c'.
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John, when it comes to you stating Einstein saying that 'light curves because the speed of light varies with position.'? First of all, if it did it wouldn't be a local constant. But it is under any and all uniform motion. "the speed of light is only guaranteed to have a value of 299,792,458 m/s in a vacuum when measured by someone situated right next to it." What that states is that it is a local definition. And that's the one working, as soon as you connect 'c' to become your local clock. If you instead try to measure between two defined anchors of matter moving from each other you can define the light otherwise, the same if you're moving towards the light source. But in a local 'two way mirror experiment' (uniform motion) it won't matter for you, there you must find 'c'. And there it won't matter what 'speed' you define yourself to either. So 'c' is a local constant, unless we assume Einstein to invalidate SR? But GR is built on 'c' too.
"Galilean relativity implies that, if a physicist on a station platform performs a mechanical experiment, and another in a smoothly passing train performs the same experiment, the two obtain identical results. (The laws of mechanics are the same in two different inertial frames.)
Einstein's principly of relativity is just like Galileo's, except that now the experiment can be either a mechanical experiment or an electromagnetic experiment. The physicist on the train measures the electric field produced by putting charges on metal conductors and the magnetic field produced by a current in a coil of wire. She will get the same result with her apparatus as would another physicist, on the platform, with similar equipment. Einstein's principle of relativity is just a generalisation of that of Galileo and Newton. If you forget about the source of the light, a light wave passing is just an experiment involving electric and magnetic fields and so its speed must be that given by the electricity and magnetism experiments. Experimentally, we find that the speed of the source does affect some things about the wave (its wavelength changes: the Doppler effect) but it doesn't influence the speed. "
And
"Einstein talked about the speed of light changing in his new theory. In the English translation of his 1920 book "Relativity: the special and general theory" he wrote: "according to the general theory of relativity, the law of the constancy of the velocity [Einstein clearly means speed here, since velocity (a vector) is not in keeping with the rest of his sentence] of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [...] cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity [speed] of propagation of light varies with position." This difference in speeds is precisely that referred to above by ceiling and floor observers.
In special relativity, the speed of light is constant when measured in any inertial frame. In general relativity, the appropriate generalisation is that the speed of light is constant in any freely falling reference frame (in a region small enough that tidal effects can be neglected). In this passage, Einstein is not talking about a freely falling frame, but rather about a frame at rest relative to a source of gravity. In such a frame, the not-quite-well-defined "speed" of light can differ from c, basically because of the effect of gravity (spacetime curvature) on clocks and rulers.
In general relativity, the constancy of the speed of light in inertial frames is built in to the idea of spacetime being a geometric entity. The causal structure of the universe is determined by the geometry of "null vectors". Travelling at the speed c means following world-lines tangent to these null vectors. The use of c as a conversion between units of metres and seconds, as in the SI definition of the metre, is fully justified on theoretical grounds as well as practical terms, because c is not merely the vacuum-inertial speed of light, it is a fundamental feature of spacetime geometry."
http://newt.phys.unsw.edu.au/einsteinlight/jw/module3_weird_logic.htm
http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html
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As for squeezing with light Claes, that's about the momentum of light. It has a wave particle duality, and you might want to think of it as particles there? Almost classical mechanics if you do I guess :) 'billiard' with particles of light. As I get it you 'squezze' something by (constantly) using lights momentum, as when using lasers acting on a object, together becoming a (light) pincher.
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Alternatively. and here's a truly weird thought. If we define 'c' to be the 'fastest there is', nothing faster, not even that magician conjuring. Then, as you learn how to use lights momentum, as we have done, you actually gets something just as 'real' as those ordinary pinchers you use. If you assume that 'c' is a clock, then that clock presenting you 'events' can't do it any better (smoother) than that. And yeah, its a weird one.
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The question, to me, is one about events, as defined through 'c', using Planck scale as a limit. If you split 'reality' into 'time frames' represented by Planck scale, what differs light pinching a object from ones ordinary pinchers of matter? We call it rest mass, and that doesn't disappear due to light becoming incoherent. But thinking of it in terms of frames, defining objects? Don't know where that one will take you :) nor me.