The Naked Scientists

The Naked Scientists Forum

Author Topic: Why does light travel forward ?  (Read 2157 times)

Offline scotty stull

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Why does light travel forward ?
« on: 11/08/2015 21:26:35 »
I do research on the separation of mass and motion. Conventional wisdom says that Energy can be transferred between objects, I may be wrong in the my way of thinking. I look at light as a form of motion that can organize and or disorganize matter as it travels.


 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #1 on: 12/08/2015 04:21:34 »
Quote from: scotty
Conventional wisdom says that Energy can be transferred between objects,...
Before you continue your studies you should read the website I created to describe what energy is all about. It's at:
http://home.comcast.net/~peter.m.brown/mech/what_is_energy.htm

Regarding your belief that energy can be transferred between objects, this is merely a convenience in the way one thinks of energy. In reality it can't really be said that energy has a location. In reality energy is merely a bookkeeping system as you'll learn if you read the webpage above. So while energy doesn't really have a position we can certainly think of it as such. But in reality what you're really doing is thinking about the actual mechanism associated with the energy. For example; if a source of EM energy emits a microwave towards a block of wood then an EM wave travels through space impinging on the wood. The molecules in the wood then start to oscillate. When the EM wave leaves the source then the energy of the source decreases. The EM wave in transit has energy associated with it and when the molecules in the wood start to oscillate then there is an increase in energy as a result. So it's very easy to visualize this as a flow of energy even though we don't actually say that the energy is located somewhere in the first place.

Quote from: scotty
I look at light as a form of motion that can organize and or disorganize matter as it travels.
Light can't do as you suggest because once it comes into contact with matter its no longer light. Think of the light in terms of a stream of photons. If part of the beam of light strikes a wall then the atoms and molecules in the wall become energized at the cost of the existence of the photons that caused it. But once it does that the photons are no longer traveling. However the photons that didn't hit the wall will keep going until/if they strike something else, etc.

However, I can't see what this has to do with your question Why does light travel forward ? Please explain what you're asking, i.e. what is it about light traveling forward don't you understand?
 

Offline scotty stull

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Re: Why does light travel forward ?
« Reply #2 on: 12/08/2015 18:38:29 »
Pmbphy ; When light travels forward is it pushed, pulled or both ? Like opening a car door conventional wisdom says that's a form of energy transfer. If energy is both mass and motion then the question can be asked, " when I open the car door " was there any mass transferred? Pmbphy thank you for helping me with this, any critical answers concerning theoretical mechanics would be helpful.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4717
  • Thanked: 154 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why does light travel forward ?
« Reply #3 on: 12/08/2015 19:48:38 »
Quote
I may be wrong in the my way of thinking.

Decidedly perverse and unnecessarily complicated. And wrong. "Form of motion" is at best unhelpful in your understanding, and at worst, meaningless.
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: Why does light travel forward ?
« Reply #4 on: 16/08/2015 05:18:58 »
Why does light move forward ?

The title of the post is extremely interesting although the actual content of the post seems to  have little to do with the title. Consider the question and the implications. Yes, light does appear to move only in the forward direction.  Why ?  The manner in which light travels has been undergoing serious study based on empirical evidence since the 17th. Century when Huygens and Newton both put forward their theories on the propagation of light.  The big problem for Huygens was not that light travelled from one point to another point, but that as it travelled it followed the inverse square law, spreading out over a progressively larger area based on the square of the distance from the source, with its intensity undergoing a reduction that was inversely proportional to the square of the distance from the source.  While Newton was concerned in the manner in which light travelled (i.e., in straight lines) Huygens was interested in why as it travelled light followed the inverse square law. The conclusion that Huygens reached was that light followed the inverse square law during its travel due to the properties of the medium through which it was travelling. Thus he assumed that space had isotropic properties – all directions in space are equal.  Any disturbance created in a sufficiently small region of isotropic space (or in an isotropic medium) propagates from that region in all radial directions. The waves created by this disturbance, in turn, create disturbances in other regions, and so on. The superposition of all the waves results in the observed pattern of wave propagation.   Quantum Mechanics has adapted this theory as part of its core philosophy,  isotropy of space  is fundamental to QED  where the wave function of any object propagates along all available unobstructed paths. When integrated along all possible paths, with a phase factor proportional to the path length, the interference of the wave-functions correctly predicts observable phenomena. Every point on the wave front acts as the source of secondary wavelets that spread out in the forward direction with the same speed as the wave. The new wave front is found by constructing the surface tangent to the secondary wavelets.



Yet consider, isn’t this theory somewhat flawed ? If space is isotropic then :

any disturbance created in a sufficiently small region of isotropic space (or in an isotropic medium) propagates from that region in all radial directions. The waves created by this disturbance, in turn, create disturbances in other regions, and so on.

Yet light is seen to propagate only in the forward direction and in fact Huygens specifically mentions this fact that light only moves in a forward direction but was able to offer no explanation for it.  The Quantum Mechanics probability theory also does not shed much light on this behavior of light because given that space is isotropic there is an equal probability (unless the data or the maths is fudged) that light will travel in all radial directions , backwards and forwards.   

This indicates that there is something seriously wrong with the Quantum Mechanics theory on the propagation of light, because no reference is made to this fact nor is any explanation forthcoming.



« Last Edit: 16/08/2015 05:24:14 by McQueen »
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #5 on: 16/08/2015 11:05:21 »
Quote from: scotty stull
Pmbphy ; When light travels forward is it pushed, pulled or both ?
Neither of those options. Being pushed or pulled refers to a force being applied. A particle that is moving at constant speed is moving force free. Since photons always move at the same speed in all inertial frames of reference there is never a force acting on them.

Regarding the meaning of push vs. pull: Push means to exert a force on an object away from you. Pull means to exert a force on an object directed towards you.

http://www.merriam-webster.com/dictionary/push
Quote
to use force to move (someone or something) forward or away from you

http://www.merriam-webster.com/dictionary/pull
Quote
to hold onto and move (someone or something) in a particular direction and especially toward yourself

These terms are rarely, if ever, used in physics. All that physics is concerned with is what is happening independent of a person being nearby.

Quote from: scotty stull
Like opening a car door conventional wisdom says that's a form of energy transfer. If energy is both mass and motion then the question can be asked, " when I open the car door " was there any mass transferred?
A door has mass. When you open a door it requires accelerating the door to get it moving and then accelerating (i.e. decelerating) it again to get it to stop. The total amount of work done is zero so there is no difference in energy between the beginning and end states. What did happen was that the center of mass of the system moved.
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: Why does light travel forward ?
« Reply #6 on: 16/08/2015 13:57:00 »
I was replying to the implications of the title and not to the content, perhaps this was not what was wanted or needed, it might even have been off topic, except that the sentence 'What does Light Travel Forward'  was present.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3923
  • Thanked: 53 times
  • The graviton sucks
    • View Profile
Re: Why does light travel forward ?
« Reply #7 on: 16/08/2015 14:09:56 »
The idea of forward motion for any particle is irrelevant. If someone shines a torch at me I can say that from my point of view the light is moving backwards towards me away from its source. So position has no meaning other than to a set of coordinates with an origin. You can set the origin at the source or any point away from it. The important point is that light comes in quanta. The quanta cannot occupy all points in a radial direction around the source as it moves away. Therefore, as a particle it has a probabilistic location that is centred upon the path of its travel. This means that the distance between these probabilities grows larger as the system evolves. This then follows the inverse square law. Unless this is understood all sorts of erroneous notions can be formed.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4717
  • Thanked: 154 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why does light travel forward ?
« Reply #8 on: 16/08/2015 18:20:23 »
Photons travelling in straight lines automatically generate an inverse square law of intensity versus distance from a point source, by simple solid geometry. The surface area of a sphere depends on the square of its radius, so the number of photons crossing unit surface area in a given time must depend on the reciprocal of the square of the radius, if the source is at the centre of the sphere.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #9 on: 16/08/2015 19:20:51 »
Quote from: McQueen
Yes, light does appear to move only in the forward direction.  Why ?
The answer to his question in the title is very simple. You made it appear way too complicated. The question is only meaningful when the light is directional in nature. In such cases the direction in which the light travels is defined as the "forward" direction for that beam of light.

Quote from: alancalverd
Photons travelling in straight lines automatically generate an inverse square law of intensity versus distance from a point source, by simple solid geometry. The surface area of a sphere depends on the square of its radius, so the number of photons crossing unit surface area in a given time must depend on the reciprocal of the square of the radius, if the source is at the centre of the sphere.
However a single photon will travel in a straight line. It's also possible to modify the light beam to make it spatially coherent.
Ideally a laser puts out a highly collimated beam, i.e. the photons are (ideally) parallel. In reality the beam is slightly divergent. That's why no laser beam will be a pencil of light forever across the universe.
 

Offline McQueen

  • Hero Member
  • *****
  • Posts: 545
  • Thanked: 6 times
    • View Profile
    • http://www.geocities.com/natureoflight/pgindex
Re: Why does light travel forward ?
« Reply #10 on: 18/08/2015 08:29:05 »
Quote
The answer to his question in the title is very simple. You made it appear way too complicated. The question is only meaningful when the light is directional in nature. In such cases the direction in which the light travels is defined as the "forward" direction for that beam of light.

I am sorry to disagree, but any normal light that is non-coherent is going to follow the inverse square law, your reference to ‘directional light’  moving in a forward direction is meaningless in this regard, the isotropy of space precludes the ‘forward’ direction. 
Further I had followed the link you had mentioned :  What is Energy?

I  confess that the comparison you have selected to illustrate energy, namely What is Life ?appears to me to be inappropriate in that it seems to be a question of not being able to see the wood for the trees!
Ever since man has had the ability to think, he has been trying to answer that very question What is Life ? with it must be said, no little success! For instance take the tiny bombardier beetle.



It has the ability to keep two substances stored separately within its body, when separated they are harmless, but when combined, they combine explosively; complete, with smoke, fire and sound! The point is that naturalists have been able to identify not only the beetle but every part of the process. No mean feat, our knowledge of nature has reached unprecedented levels thanks to naturalists like David Attenborough.  This is not an isolated instance, in almost every branch of science, our knowledge has reached extremely detailed levels. Thus mankind has made a fair attempt at trying to answer the question "what is life?" and have succeeded in answering it to a surprising degree.

It is only when dealing with extremely fundamental and vitally important topics such as the propagation of light and the propagation of electricity that the dominance of physicists like yourself, who are so caught up in mathematical abstractions as to have no hold on reality, that little or no progress has been made. The answer to what light is or as to how it, or electricity, propagate, remains as, or more vague than they were at the time when such question were  raised. Before you take umbrage at this:  LOGICALLY it is not possible to heap theory (Huygens-Fresnel) on theory (Maxwells Electromagnetic Radiation) on theory (Schrodinger’s Wave function) on theory (Planck’s Quanta) on theory ( Special relativity) and to believe that it is possible to derive any meaningful answer,  yet this is precisely what Quantum Mechanics attempts to do. To any layman it is immediately possible to see that such a course is pointless,  but for a believer   in statistical mathematics it is apparent that  great satisfaction can be derived from ruminating on what such abstractions might mean.
Quote
However a single photon will travel in a straight line. It's also possible to modify the light beam to make it spatially coherent. Ideally a laser puts out a highly collimated beam, i.e. the photons are (ideally) parallel. In reality the beam is slightly divergent. That's why no laser beam will be a pencil of light forever across the universe.
A coherent beam of light from a laser will travel for some distance without noticeable divergence, because the beam's coherence gives it a huge initial boost in intensity, after which it proceeds to fall off as the inverse of distance squared. Thus once the laser beam begins to diverge (lose coherence) it follows the inverse square law.
The theory I have put forward at this sub-forum, gives a real rational and  verifiable theory.
 

Offline scotty stull

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Re: Why does light travel forward ?
« Reply #11 on: 19/08/2015 18:56:13 »
Motion; Moment of inertia; When a wave pushes forward, the pushing effect causes a mass to deviate from going straight, and when a wave is pulled, the wave can be brought back to a node. If and when something is being pushed there will be a simultaneous opposite effect but not a pull in a simultaneous straight opposite direction, instead the mass curves back to a straight path over time. This straight path may not be in the same direction as when the mass was pushed forward ( Inverse Square Law ). Positive Motion of Inertia : Negative Motion of Inertia if there is such a thing.
 

Online Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1919
  • Thanked: 123 times
    • View Profile
Re: Why does light travel forward ?
« Reply #12 on: 20/08/2015 12:41:57 »
I am sorry to disagree, but any normal light that is non-coherent is going to follow the inverse square law, your reference to ‘directional light’  moving in a forward direction is meaningless in this regard, the isotropy of space precludes the ‘forward’ direction. 
I take a different view. English usage allows for the direction of travel towards an objective or away from an origin to be considered as forwards. Given the context:

Photons travelling in straight lines automatically generate an inverse square law of intensity versus distance from a point source, by simple solid geometry.
Photons travelling from a point source can be considered as going forwards. They will travel along straight lines radially from the source. Even if we use the wave convention we can consider that any point on the sphere is moving forwards, away from the source.

However, I think the real problem is that we are all struggling to understand exactly what question the OP is asking and the following post really doesn't help to clarify.

Motion; Moment of inertia; When a wave pushes forward, the pushing effect causes a mass to deviate from going straight, and when a wave is pulled, the wave can be brought back to a node. If and when something is being pushed there will be a simultaneous opposite effect but not a pull in a simultaneous straight opposite direction, instead the mass curves back to a straight path over time. This straight path may not be in the same direction as when the mass was pushed forward ( Inverse Square Law ). Positive Motion of Inertia : Negative Motion of Inertia if there is such a thing.
Scotty, I am struggling to understand your post and exactly what you are asking.
I don't understand your reference to inverse square law and a mass being pushed forward. Can you give examples of situations where a wave causes a mass to deviate? How does this relate to your question about light?
Moment of inertia refers to rotating bodies, where does this come in?
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #13 on: 21/08/2015 01:17:27 »
Quote from: scotty
Motion; Moment of inertia;
What do those two things have to do with each other regarding this subject?

Quote from: scotty
When a wave pushes forward, ..
Why do you keep using the term "push" when such a term should never be used in physics? That's a layman's term. You're talking about exerting a force. But no wave will exert a force unless there is something to exert a force on. What is this thing that has a force on it by the wave?

Quote from: scotty
...the pushing effect causes a mass to deviate from going straight, and when a wave is pulled, the wave can be brought back to a node.
I can understand what you mean by "pushing" here but what do you mean by "pulled"?

Quote from: scotty
If and when something is being pushed there will be a simultaneous opposite effect ...
Since when? You must have Newton's 3rd law in mind. While that holds true in Newtonian mechanics Newton was unaware of electrodynamics and in those cases the 3rd law doesn't hold true.

Quote from: scotty
Positive Motion of Inertia : Negative Motion of Inertia if there is such a thing.
Those terms have no meaning.
 

Offline scotty stull

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Re: Why does light travel forward ?
« Reply #14 on: 21/08/2015 19:09:15 »
Duality of pure motion devoid of mass; Always in the act of being positive and negative at the same time and quantity. With mass then being in the same or different form as well as a same or different time with respect to each other.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #15 on: 22/08/2015 11:48:40 »
Duality of pure motion devoid of mass; Always in the act of being positive and negative at the same time and quantity. With mass then being in the same or different form as well as a same or different time with respect to each other.
Then as you speculated in reply #11 there is no such thing.
 

Online Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1919
  • Thanked: 123 times
    • View Profile
Re: Why does light travel forward ?
« Reply #16 on: 26/08/2015 08:58:20 »
Duality of pure motion devoid of mass; Always in the act of being positive and negative at the same time and quantity. With mass then being in the same or different form as well as a same or different time with respect to each other.
This is dissapointing, I thought from the opening post you might have a serious question.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2762
  • Thanked: 38 times
    • View Profile
Re: Why does light travel forward ?
« Reply #17 on: 27/08/2015 03:58:31 »
Duality of pure motion devoid of mass; Always in the act of being positive and negative at the same time and quantity. With mass then being in the same or different form as well as a same or different time with respect to each other.
This is dissapointing, I thought from the opening post you might have a serious question.
I can't even make sense of what he's posting.
 

Online Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1919
  • Thanked: 123 times
    • View Profile
Re: Why does light travel forward ?
« Reply #18 on: 27/08/2015 09:22:01 »
I can't even make sense of what he's posting.
Me neither, I had hoped it was a translation problem and there was a real question behind it. No hope of that.
 

Offline scotty stull

  • Jr. Member
  • **
  • Posts: 27
    • View Profile
Re: Why does light travel forward ?
« Reply #19 on: 16/09/2015 19:35:51 »
Light travels forward because the medium that it travels in allows it to do so. The critical question is, what are the dynamics involved in this medium that allows light to travel forward ? When light travels vast distances in outer space, will that light source obey the inverse square law ? Even if light does obey the inverse squre law there is mechanics involved that allows light to do so.
 

The Naked Scientists Forum

Re: Why does light travel forward ?
« Reply #19 on: 16/09/2015 19:35:51 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length