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  1. Standard member vivify
    rain
    09 Mar '15 03:27
    Why is light able to continually move forward for billions of years? What is happening that light has the energy to move throughout the universe for what seems like an unlimited amount of time? After all, we do see galaxies that are billions of light years away from us.

    Is light some kind of infinite energy source?
  2. 09 Mar '15 05:47
    Originally posted by vivify
    Why is light able to continually move forward for billions of years? What is happening that light has the energy to move throughout the universe for what seems like an unlimited amount of time? After all, we do see galaxies that are billions of light years away from us.

    Is light some kind of infinite energy source?
    You are thinking of 'work', not 'energy'.
    Energy is a conserved quantity.
  3. Standard member vivify
    rain
    09 Mar '15 06:22
    Originally posted by twhitehead
    You are thinking of 'work', not 'energy'.
    Energy is a conserved quantity.
    Is the movement of light consisted 'work'?
  4. 09 Mar '15 06:38
    Originally posted by vivify
    Is the movement of light consisted 'work'?
    No. The energy of a moving photon does not change as it moves through the vacuum.
  5. 09 Mar '15 06:46
    Originally posted by vivify
    Is the movement of light consisted 'work'?
    No.
    I have to point out that maintaining the movement of anything doesn't take work. Newtons First Law of Motion.

    http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

    Earth doesn't need jet engines to keep it going around the sun.

    Even a baseball flying through space would continue on its path for just as long as light can as long as it doesn't interact too strongly with objects around it. Light tends to go further and straighter because it interacts less.
  6. 09 Mar '15 08:34
    Originally posted by vivify
    Why is light able to continually move forward for billions of years? What is happening that light has the energy to move throughout the universe for what seems like an unlimited amount of time? After all, we do see galaxies that are billions of light years away from us.

    Is light some kind of infinite energy source?
    once light is created, nothing needs to 'power' it for it to move through space for no energy is expended for it to move through space.
    It is not as if it is like a solid object moving though some kind of atmosphere where it is exposed to friction force against its movement and thus requires a constant energy source to maintain its current speed!
  7. 09 Mar '15 12:42
    Originally posted by twhitehead
    No.
    I have to point out that maintaining the movement of anything doesn't take work. Newtons First Law of Motion.

    http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

    Earth doesn't need jet engines to keep it going around the sun.

    Even a baseball flying through space would continue on its path for just as long as light can as long as it doesn' ...[text shortened]... ngly with objects around it. Light tends to go further and straighter because it interacts less.
    yes, but hasn't it been proven that light "bends" around objects with great amt. of gravity ? Is that some form of friction or energy working against light while it tries to move thru space in a straight line ?
  8. Standard member sonhouse
    Fast and Curious
    09 Mar '15 13:04
    Originally posted by woadman
    yes, but hasn't it been proven that light "bends" around objects with great amt. of gravity ? Is that some form of friction or energy working against light while it tries to move thru space in a straight line ?
    Not friction. Light simply follows the curvature of space. Gravity IS a curve in space so light just follows like a ball rolling down a hill that has bumps and holes in it, the ball just follows the path it encounters on its journey downhill.

    Of course, the ball stops when it gets to the bottom of the hill but light just keeps going on its new course.

    You can think of gravity as bending a spandex sheet, which is a decent approximation in a 2 dimensional way.

    Of course the real bending is 3 and 4 dimensional. 4 dimensional because it also changes the flow of time. Close to a mass, time slows down, away from the object, time speeds back up closer to what it would be flowing, in a totally mass free system. Of course there can never be any place in the entire universe that is totally free of the effects of mass.

    You get into near space, go away from Earth and you are now dealing with the gravity bending space effect from the sun.

    You keep going and say you head due north out of the plane of the galaxy, even if you are a million light years away from the milky way, you are still on a curve created by the accumulation of all the stars in our milky way galaxy. You can see that by the fact Andromeda galaxy and the milky way are crunching to a crash in a billion or so years, space is bent in such a way as to be attracting entire galaxies and their attendant dwarf satellite galaxies like the large magellanic cloud and the small magellenic, they are captured by the gravity of the milky way. Space is bent around those objects in such a way as they fell into our galaxy and now the original galaxy is shattered and spread out in a million pieces, a shadow of their former selves, not even close to the more or less flatness of our own galaxy. So even if you got out of the milky way a million light years away there would still be the gentle bending of space from the mass of the entire galaxy added up together.
  9. Standard member vivify
    rain
    09 Mar '15 13:43
    Originally posted by twhitehead
    No.
    I have to point out that maintaining the movement of anything doesn't take work. Newtons First Law of Motion.

    http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion

    Earth doesn't need jet engines to keep it going around the sun.

    Even a baseball flying through space would continue on its path for just as long as light can as long as it doesn' ...[text shortened]... ngly with objects around it. Light tends to go further and straighter because it interacts less.
    Okay. Let's say that the earth was as large as the galaxy itself. In that scenario, for light to move to one end of the earth to the other would be considered work because of gravity, right?
  10. 09 Mar '15 13:46 / 1 edit
    Originally posted by vivify
    Okay. Let's say that the earth was as large as the galaxy itself. In that scenario, for light to move to one end of the earth to the other would be considered work because of gravity, right?
    even if the Earth was transparent so that could happen, no. Remember, photons of light have no mass therefore it isn't like the potential energy that is lost when you drop an object with mass onto the surface of the Earth!
  11. 09 Mar '15 13:50
    Originally posted by sonhouse
    Not friction. Light simply follows the curvature of space. Gravity IS a curve in space so light just follows like a ball rolling down a hill that has bumps and holes in it, the ball just follows the path it encounters on its journey downhill.

    Of course, the ball stops when it gets to the bottom of the hill but light just keeps going on its new course.
    ...[text shortened]... would still be the gentle bending of space from the mass of the entire galaxy added up together.
    Interesting stuff..and thanks for the examples. Are scientists interested in an area of the cosmos that is the least affected by gravity ? Where space is the most "empty" I know that Hubble has looked into dark, empty space and found multiple galaxies. They were actually moving away from us faster than the speed of light, which is why that area is so dark.
  12. Standard member DeepThought
    Losing the Thread
    09 Mar '15 15:01
    Originally posted by vivify
    Okay. Let's say that the earth was as large as the galaxy itself. In that scenario, for light to move to one end of the earth to the other would be considered work because of gravity, right?
    Suppose a photon (particle of light) has to climb out of a gravitational well. To do so it has to use up some of its kinetic energy. The energy of the photon is given by E = hf, where f is the frequency and h is Planck's unreduced constant. So the frequency of the light decreases.

    As an incandescent object falls into a black hole an asymptotic observer (one very distant from the black hole) will see the light it emits shifted to the red end of the spectrum as the object gets closer and closer to the event horizon.

    As to the photon's speed it is important to understand that that depends on the coordinate system a given observer is using. In the coordinates natural to the asymptotic observer the photon will appear to be moving at less than the speed of light when it is emitted. However as far an observer co-moving with the object falling into the hole is concerned, who has a different set of natural coordinates, the photon is going at the speed of light when its emitted and actually seems to speed up (in so far as one can see a photon) as it moves up out of the gravitational well. This is because coordinates are arbitrary things we impose on space-time. The actual physical distance travelled only corresponds to the coordinate distance travelled near the observer for whom the coordinate system is natural. So, as far as an asymptotic observer is concerned out-moving photons near the event horizon are almost stationary and in-moving photons are travelling at almost twice the speed of light.
  13. 09 Mar '15 20:51 / 4 edits
    Originally posted by woadman
    I know that Hubble has looked into dark, empty space and found multiple galaxies. They were actually moving away from us faster than the speed of light
    I don't see how observing galaxies moving away from us over the speed of light (c) could be possible. Relativity tells us that we cannot ever observe anything going over c (in any frame of reference ) that is actually going over c (i.e. it isn't a mirage ) + if they where moving away from us over c then I presume we wouldn't see them because the Doppler shift.
    Certainly I know the equations tell us that light from an object hypothetically moving at exactly one c exactly in the direction away from you will have a Doppler shift that would make the wavelength of that light from your frame of reference infinite! And that would mean there would be no such light for you to see!
  14. Standard member DeepThought
    Losing the Thread
    09 Mar '15 21:27
    Originally posted by humy
    I don't see how observing galaxies moving away from us over the speed of light (c) could be possible. Relativity tells us that we cannot ever observe anything going over c (in any frame of reference ) that is actually going over c (i.e. it isn't a mirage ) + if they where moving away from us over c then I presume we wouldn't see them because the Doppler shift. ...[text shortened]... ur frame of reference infinite! And that would mean there would be no such light for you to see!
    What you've written is correct, however, the program makers may have been saying something subtly different. Space is expanding, the speed of recession is proportional to the distance, this is the physical content of Hubble's law. So at some great distance galaxies are moving away from us at the speed of light. As you correctly state they are infinitely redshifted, we cannot see them. This produces as cosmological event horizon beyond which we cannot see objects.

    What the program makers might have meant is that because the galaxies are so distant we are seeing them as they were 12 or 13 billion years ago. In the meantime they have moved through the cosmic event horizon and we will never see the light that they are emitting today.

    Alternatively they were talking pseudo-scientific crap and got it wrong, it's hard to tell without seeing the program. I'm a little suspicious as what woadman seemed to be describing was a great void and they aren't that distant (the Boötes void is 700 million lightyears away) so references to the speed of light are suspicious.
  15. 10 Mar '15 00:43
    Originally posted by vivify
    Okay. Let's say that the earth was as large as the galaxy itself. In that scenario, for light to move to one end of the earth to the other would be considered work because of gravity, right?
    I'm a bit curious. What if ... purely hypothetical nonsense ... then ... force of light would react with parameter X.

    You are talking about something EXTREMELY HEVY.

    Space is governed by mathematical rules. THIS SUPERHEVY EARTH thing seem to break one. Note. I am not sure it does.

    Due to statistical mathematics there are configurations of abundance of large quanteties of space matter. We call these configurations planets. Planets and stars are two very similar things. Both of which contain matter.

    Now we have the gravitational force which act on this matter. Statistical mathematical rules say that. Planets comes in all forms due to statistics.

    STATISTICS TELLS US THAT THERE ARE MORE CONFIGURATIONS OF MATTER IN SPACE THAT ARE FORMED AS PLANETS THAN THOSE CONFIGURATIONS WHICH DO NOT HAVE PLANETS.

    Else we would have space which was more like common cow milk. Homogenized. Everything about equal distance to eachother everywhere in space. Gravitational force form planets because there are more configurations of 'planets in a universe' than 'milk like universes'.