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What is the force that causes it to move and why does it maintain the speed for so long? If it has no mass, why is it effected by mass?

Qmechanic
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Richard Hesketh
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  • Physics doesn't answer "why" questions. It seems to me, though, that you are really asking "How can there be so little interaction between light and matter, that light can travel so far without being scattered?". Why is that a better question? Because in physics nothing happens without a cause. Light isn't scattered, unless there is something there to scatter light. When light passes cosmic distances without being scattered, we therefor know, that there wasn't enough matter to scatter it, between the light source and us. – CuriousOne Aug 28 '14 at 18:43
  • @CuriousOne can you elaborate on your first statement? I see nothing wrong with asking "Why?" – HDE 226868 Aug 28 '14 at 18:45
  • This is a duplicate of many questions on the site, but I can only choose one in the close box. I'll see if I can edit in some other links. – David Z Aug 28 '14 at 18:48
  • @HDE226868: Unfortunately, many "why" questions seem to imply, that there is some sort of grand plan of the universe, and that physics is out to discover that plan. That is simply not so. Physics is about finding suitable approximations to observations, including ones that contradict each other in almost every possible way, and are still considered excellent physics. IMHO it is important for layman to internalize, that it is much better to ask "How can we explain X?" rather than to phrase the question as "Why is X so?". – CuriousOne Aug 28 '14 at 19:13
  • @CuriousOne So you mean the "why" questions seem to edge into the domain of philosophy (i.e. "Why are we here?")? I agree with that, and that there are many cases in which "how" trumps "why", but I don't think that that applies here. – HDE 226868 Aug 28 '14 at 19:16
  • @HDE226868: In my observation it matters who is asking the questions. Physicists are often sloppy enough to ask "why", when they really mean "how" and there is no harm in that, since we all know intuitively what we mean. I do not think that the OP has that intuition. He seems to have a model of the world in which everything slows down by itself without interaction. One can not do physics successfully in such a framework, and it is important for him to internalize, that there is no effect without cause. The kind of "why" question in the original post is highly counterproductive to that. – CuriousOne Aug 28 '14 at 19:23
  • @CuriousOne I think you're making some rather derogatory remarks toward RichardHesketh that are unnecessary ("layman"? Why would you assume that?). This is getting opinionated, and at any rate, I think the whole matter is moot at this point. – HDE 226868 Aug 28 '14 at 19:25
  • @HDE226868: We were all layman at one point. I had exactly the same questions as Richard to my physics teacher. The solution to my questions wasn't a matter of physics, but of my personal insight, that my "lossy" model of the world was simply wrong. It is a non-trivial (and to some extent intellectually traumatic) experience, that the world is simply not the way we think it is based on our evolved internal model of Newtonian mechanics in a 1 bar nitrogen/oxygen atmosphere subjected to a constant 1g acceleration pointing towards the floor. – CuriousOne Aug 28 '14 at 19:35
  • It was not a 'why question' it was a 'What causes light to travel' question. The secondary part was 'What is the force that causes it to move and why does it maintain the speed for so long? If it has no mass, why is it effected by mass? Change that to 'What is the force that causes it to move and what causes it to maintain the speed for so long? If it has no mass, what causes it to be effected by mass? The main question that I would like an answer for is 'What causes light to travel?' Hope this helps, Richard – Richard Hesketh Aug 29 '14 at 21:33
  • There is no "force" that causes light to travel. But yes, that comment does help. – HDE 226868 Aug 29 '14 at 21:49

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