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Thread: A question about time and light

  1. #1 A question about time and light 
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    Im not quite sure if this question belongs in this section, but will place it here for lack of a better place.

    In photography, light is focused through a lens, slows down, bends, and is recorded on film to create an image of the past.

    Is this process possible because the light that was captured is gone, and since the moment that it was recorded we have traveled from that point in space? So, if we were to completely stop our movement in space, (our galaxy and the universe as well) would light continue to record time, and our eyes, like film, see the future?

    Of course this is not possible, I am just trying to understand our preception of time and its relation to light. We are able to revel in the past through manipulations of light like radio, TV, and such but is time set or fine tuned to the speed of light? Also, interesting is the function of Melatonin, our internal time keeper governed by light, responsible for a variety of functions in many different organisms, which also gives us a since of jet-lag when we travel in time.

    This is a very incomplete thought and highly irrational I know, but I am just curious. Hope you have the time to answer this question or could shed some light on the subject. Thanks.


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  3. #2 Re: A question about time and light 
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by inite
    In photography, light is focused through a lens, slows down, bends, and is recorded on film
    Light never slows down. Light never speeds up. Light travels at one speed. It travels at c.

    Now, there are times when the apparent speed of light slows down, but the photons themselves travel at a constant c. What you are referring to (I think) is when light gets absorbed and re-emitted by some substance or material... it appears to us perceptually to have slowed down... However, most assuredly, it has remained at a constant speed.


    Quote Originally Posted by inite
    Is this process possible because the light that was captured is gone, and since the moment that it was recorded we have traveled from that point in space?
    I'm not sure about the second half, but the light is not "gone." It has simply changed forms. It has transferred its energy on to a photoreceptor or a chemical film and led to a cascade of other effects, but it is not gone. It has changed forms.


    Quote Originally Posted by inite
    So, if we were to completely stop our movement in space, (our galaxy and the universe as well) would light continue to record time,
    If all movement stopped, then there would be no such thing as time. The stopping of all movement in the entire universe is equivalent to frozen time, so there is nothing to record. Now, there are other issues here such as the fact that there is no such thing as absolute time or absolute space, so the concept of stopping it all is somewhat flawed. You have to realize that when you attempt to describe systems which are not possible then it is also not possible to use existing physics to describe those systems. Physics only applies to things which might actually exist or be possible in nature.


    Quote Originally Posted by inite
    and our eyes, like film, see the future?
    Like I said, the only way to freeze everything is to stop time, so the concept of "future" becomes meaningless.


    Quote Originally Posted by inite
    Of course this is not possible, I am just trying to understand our preception of time and its relation to light.
    I don't understand.


    Quote Originally Posted by inite
    We are able to revel in the past through manipulations of light like radio, TV, and such but is time set or fine tuned to the speed of light?
    I don't understand. We don't see the past. We see light reaching us that took time to travel, so we are experiencing seeing that object as it appeared in the past.


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  4. #3  
    Forum Cosmic Wizard icewendigo's Avatar
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    about speeed of light being constant, what happens to light inside a black hole? Does it head to the center? once in the center does it still move at the same speed?
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  5. #4  
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by icewendigo
    about speeed of light being constant, what happens to light inside a black hole? Does it head to the center? once in the center does it still move at the same speed?
    Unknown. Our current models result in singularities when we reach the center of a BH, so we cannot say with any confidence what happens after a given point. We need some new equations and math that is able to incorporate both relativity and QM (akin to quantum gravity) to better address your question.
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  6. #5  
    Moderator Moderator Dishmaster's Avatar
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    It is possible that light will be absorbed by the most certainly ionised matter.
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  7. #6  
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    Quote Originally Posted by icewendigo
    about speeed of light being constant, what happens to light inside a black hole? Does it head to the center? once in the center does it still move at the same speed?
    Time stands still in the black hole, hence it has evaporated before anything moved in it, seen from the inside. Questions? Answers?
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  8. #7  
    Forum Freshman 6nqpnw's Avatar
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    Does anyone else agree that the relationship between time and light is often confused? Isn't light used simply as a reference point for time (being that light is constant and not dynamic / variable / changing)?

    Without know better how to articulate time and light, but if you travel faster than light, you're just moving faster than an image (light reflected off of matter), having NO effect on the matter itself.

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  9. #8  
    Moderator Moderator Dishmaster's Avatar
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    Quote Originally Posted by 6nqpnw
    Does anyone else agree that the relationship between time and light is often confused? Isn't light used simply as a reference point for time (being that light is constant and not dynamic / variable / changing)?

    Without know better how to articulate time and light, but if you travel faster than light, you're just moving faster than an image (light reflected off of matter), having NO effect on the matter itself.

    - mudbud
    You are correct in the sense that the speed of light is independent of any reference frame. This is the constant in the relations between space and time. Remember, you cannot separate space and time, because besides time dilation there is also length contraction. And these entities do depend on reference frames - the speed of light does not.
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  10. #9  
    Forum Freshman 6nqpnw's Avatar
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    approaching near speed of light = decreased matter decay (time dilation) + decreased length (length contraction) + increased mass (mass increase :? )

    This is all too much for me in one day. Gonna sleep on it.

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  11. #10 Re: A question about time and light 
    Forum Freshman ISandalphon's Avatar
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    Quote Originally Posted by inow
    Quote Originally Posted by inite
    In photography, light is focused through a lens, slows down, bends, and is recorded on film
    Light never slows down. Light never speeds up. Light travels at one speed. It travels at c.
    >>Brevity Snip<<< However, most assuredly, it has remained at a constant speed.
    .


    I am puzzled about several of your answers. The notation (c) is the speed of light in a vacuum, the c denoting constant, because lights velocity is constant in a vacuum. Light is slowed when it encounters an transparent medium, water, plastics, atmospheres like earths, glass etc. The ratio of the change in velocity is called the refractive index of the medium. BTW its always greater than one, except in special circumstances which we need not go into here for brevity's sake. I'm not a scientist but that was my teaching.

    We can theorize what happens to light in general terms after it crosses the event horizon of a black hole. At least we think it will not emerge again because the escape velocity of a black hole would exceed the speed of light. However you are correct in that we can not know for sure what happens, because our physics do not apply past the event horizon of the BH. There are several more statements you made I would like clarification on but will wait until you expand on the light speed issue.

    IS
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  12. #11  
    Forum Freshman ISandalphon's Avatar
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    Quote Originally Posted by 6nqpnw
    Does anyone else agree that the relationship between time and light is often confused? Isn't light used simply as a reference point for time (being that light is constant and not dynamic / variable / changing)?

    Without know better how to articulate time and light, but if you travel faster than light, you're just moving faster than an image (light reflected off of matter), having NO effect on the matter itself.
    - mudbug
    Probably the reason that the speed of light is associated with time is because of the relativistic effects of velocity as experienced by at least two observers. It makes time travel, ie time dilation obvious and profound. Mass can be exchanged for velocity because the gravity created by mass bends space time, the larger the mass (or the higher the velocity) the greater and more profound the effect on time.

    Now, time and space are intimately linked, but not time and light. It's the spacetime we all know and love. Most look at space-time like a rubber sheet with the massive bodies like planets and stars deforming the sheet (spacetime) proportional to their mass. If you were an stationary astronaut watching your fellow piloting his craft into a (non rotating) black hole by allowing the gravity to pull him, he would appear to speed up but then slow as he approached the event horizon. Eventually his spaceship would appear to stop before entering the black hole and remain there for your life time and even our suns life time! This is because his craft would be approaching the speed of light (relative to you) as it was pulled into the black hole!

    However time according to your buddies watch would pass normally! But if your bud the astronaut could be watching you in his super telescope as he drew closer and closer to the black hole it would seem as if everything was speeding up crazily, into a blur. He would see you grow old in a second, as his craft neared light speed as it drew closer to the black hole, then he would see you and die and even see our sun turn into a white dwarf, and die...

    Weird huh?

    IS
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  13. #12 Re: A question about time and light 
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by ISandalphon
    I am puzzled about several of your answers. The notation (c) is the speed of light in a vacuum, the c denoting constant, because lights velocity is constant in a vacuum. Light is slowed when it encounters an transparent medium, water, plastics, atmospheres like earths, glass etc.
    No, actually. As I described above, it's not. The speed of light remains the same. The only thing which changes is its apparent speed. Each photon will still move at c, but it is being absorbed and re-emitted as it interacts with the aforementioned medium (water, plastic, glass, etc), and this makes it appear to have slowed down.

    I can assure you, though, the photon is still traveling at c, and c only between each absorption and re-emission.
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  14. #13  
    Forum Freshman ISandalphon's Avatar
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    I don't like to disagree, but feel I must. First, we should agree that c indicates the speed of light in a vacuum. Specifically in a vacuum. If you were to say that the speed of light through say water was c, or that the speed of light through glass was c you would be mistaken. Additionally light can be either a photon (a massless, ie zero rest mass, zero charge elementary particle) or a wave. Here is a more detailed explanation with a link to the site ;

    "Essentially the speed of radio and other electromagnetic waves too, the speed of light depends on transmission medium. The maximum speed, labelled c and often referred to as the speed of light without qualification, occurs in a vacuum, it equals 299?792?458 m·s-1 (1.079?252?85~ × 109 km/h, 670.616?629~ × 106 m.p.h.), the first figure being precise since the 1983 re-definition of the metre."


    http://www.answers.com/topic/speed-of-light

    I provided the link and highlighted the relevant parts for your all's convenience and to validate my statements, I realize you don't know me so I hope the link (one of thousands) will lend credence to the stranger, ie me. Thanks for your reply and I hope we can come to a meeting of minds :wink:

    IS
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  15. #14  
    Forum Freshman 6nqpnw's Avatar
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    PRO-CONSTANT ::: http://en.wikipedia.org/wiki/Light :::
    Light always travels at a constant speed, even between particles of a substance through which it is shining. Photons excite the adjoining particles that in turn transfer the energy to the neighbor. This may appear to slow the beam down through its trajectory in realtime. The time lost between entry and exit accounts to the displacement of energy through the substance between each particle that is excited.

    PRO-SLOW::: http://curious.astro.cornell.edu/que...php?number=630 :::
    However, the speed of light is not constant as it moves from medium to medium.

    PRO-CONSTANT::: http://www.newton.dep.anl.gov/askasc...0/phy00111.htm:::
    The light does not actually travel more slowly when in material. The light
    travels from atom to atom. An atom absorbs the light for a short time and
    then releases it. These short delays are what cause the apparent slowing.

    PRO-SLOW::: http://www.pbs.org/wgbh/nova/einstei...ght/index.html:::
    The speed of light is constant only in a vacuum, a place where there's no matter, like the vast emptiness of space. Here on Earth, the speed of light can slow down.

    Some clarification is in order...DISHMEISTER...please enlighten me <<< [me so punny ]

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  16. #15  
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    Both alternatives do not contradict each other. The first link provides the explanation, i.e. the speed of light seems to alter its speed, but light is constantly absorbed and re-emitted. Each of those processes takes some time leading to the delay. An extreme example is described here:
    Photon travel time inside the sun
    or here:
    Ancient sunlight
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  17. #16  
    Forum Freshman ISandalphon's Avatar
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    From the web ; "The speed of light depends on the medium through which the light travels. In empty space, the speed is 186,000 (1.86 X 105) miles per second. It is almost the same in air. In water, it slows down to approximately 140,000 (1.4 X 105) miles per second. In glass, the speed of light is 124,000 (1.24 X 105) miles per second. In other words, the speed of light decreases as the density of the substance through which the light passes increases."

    http://www.tpub.com/neets/book10/39h.htm


    Wiki needs an citation, I don't trust it as a source because anyone can post information there. I have been embarrassed because the information provided was wrong and I used it in two papers. Additionally, no one has not addressed the incorrect usage of the meaning and notation of (c). And that is that (c) is the speed of light in a vacuum. You could not accurately say that (c) represented the speed of light in glass for example. If lights velocity did not change there would be no need to indicate that c is the speed of light in a vacuum eh? The term light means the electromagnetic spectrum and (could) include wave and particles ie photons (light can be either or). If a photon bounces slows in a transparent medium the photon still is moving at the velocity of light, but the speed of light is slower! It sounds confusing but think about it.

    I will comment on the rest of the pro con thing ASAP, in closing if it takes longer for light to go to point a to point b it has effectively slowed correct? The duality of light (being a wave or a particle etc) and its various forms such as x rays also play a role in the speed when it encounters some transparent substances.

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  18. #17  
    Geo
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    Quote Originally Posted by Dishmaster
    Both alternatives do not contradict each other. The first link provides the explanation, i.e. the speed of light seems to alter its speed, but light is constantly absorbed and re-emitted. Each of those processes takes some time leading to the delay.
    So inside a black hole, there's so much matter that light has to interact with it all, before that light will be emitted?

    Will blackholes eventually emit light? over huge time scales?

    Inside a black hole then, if light travels so slow, distances which we perceive as MPc, would be picometers, which would mean time is so slow that light won't ever escape.

    Has c, increased/decreased during the evolution of the Universe.
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  19. #18  
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    Quote Originally Posted by Geo
    Quote Originally Posted by Dishmaster
    Both alternatives do not contradict each other. The first link provides the explanation, i.e. the speed of light seems to alter its speed, but light is constantly absorbed and re-emitted. Each of those processes takes some time leading to the delay.
    So inside a black hole, there's so much matter that light has to interact with it all, before that light will be emitted?

    Will blackholes eventually emit light? over huge time scales?
    No. This is an entirely different situation, because the gravity is too strong so that the photons cannot escape, regardless of what is going on inside the event horizon.
    Quote Originally Posted by Geo
    Inside a black hole then, if light travels so slow, distances which we perceive as MPc, would be picometers, which would mean time is so slow that light won't ever escape.
    No. I don't see how those things are related. Take the similar example of the sun. The sun does not appear smaller, just because the photons take so long until they escape the photosphere.
    Quote Originally Posted by Geo
    Has c, increased/decreased during the evolution of the Universe.
    Good question. There are some indications that this might have happened. At least it cannot be ruled out entirely. So, it is an open question.
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  20. #19  
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    I wanted to retract the reference I made to light being “slowed” during the photographic process. I understand that the speed of light is constant and remains so through which the particles it flows (refection/transmission/absorption/re-emission). Although I am not completely certain, I think silver is the photochemical that produces the photoelectric effect in photography but would have to read further into the process of film development.

    “the light is not "gone." It has simply changed forms.” This demonstrates that I really should better understand the photographic process before I decide to use it as a reference to the point I was trying to make. I meant that some packets of photon particles are focused through the lens of a camera, while others do not travel in the camera’s direction and so are not “captured.” Thus, the particular light wave that has reached an object from the sun, took 8 min to travel from the surface of the sun (or 10,000-170,000 years from the core) to that object (on earth), yet not all particles of that light wave were captured by the lens and so that particular light wave is “gone” in the sense that it will never again be emitted from the sun. It is unique like that particular moment in time is unique, because both the light and earth are traveling through spacetime? This question is very difficult to express and I did a lousy job the first time so please allow me to expand a bit… Time is distance plotted on the spacetime grid and light (EM) is the “speed limit,” correct? So, time is traveling from point a to point b, constantly increasing the distance from and to both points, much like the way we experience time, ever progressing, no past nor present, but a constant and gradual move toward point b. We are bounded by the speed of light (macro), yet constantly experience it (micro).

    “(light reflected off of matter), having NO effect on the matter itself” Light is the visual spectrum of EM (energy), and is it not the energy between atoms that constitute matter? Heat flow between compounds can alter states of matter, and light reveals to us those states. Just as heating and cooling elements may alter their states, bending light allows us to examine the deep regions of space or minute intracellular processes. Living organisms demonstrate the photoelectric effect as well through the electron transport chain which renders ATP. So, really my question has less to do with photography and more to do with how energy flow (and not just light from the sun) through spacetime on the micro/macro scale arrives us at point b. Is the future set, and if so, how does it materialize? Could instructions for the future be encrypted within EM awaiting matter to translate? (and I do not imply design, more so reactive states) But since the universe is a closed system, the macro has no effect on the micro because of distance?

    Also, in reference to the Ancient Sunlight link, does the earth’s core experience a similar effect when generating the magnetosphere?
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