flip wrote:Do you know what mechanical force is?
Yes, but you apparently don't, because mechanical force as you're thinking of it has NOTHING to do with gravity: it's the direct application of force between two objects that are in contact with each other. It's not even a rigorously-defined term: do a search for "mechanical force" on Wikipedia and you come up with bupkis. (And really, if you're going to source something, try doing better than a random Ask.com result.) Mechanical
energy, on the other hand, is a very well-defined concept, as the sum of the kinetic and potential energies of an object.
flip wrote:EDIT: "According to Einstein's theory, light can also create gravity even though it is not made up of matter. It's just energy, but it can create gravity."
This is true in a certain sense, and I'll admit that what I stated earlier on this point is incorrect: a beam of light would produce a gravitational field. What I said about photons having no mass is true, but where I screwed up is in the fact that the term "mass" by itself refers to different concepts depending on the circumstances. A photon does not have any
rest mass, which is defined as the mass of an object when it is not moving: this is the mass that appears in Einstein's famous equation, and gives an object its rest energy via the mass-energy equivalence described in that equation. Objects in motion will always have an energy above their rest energy, and so through that equivalence can be viewed as having a
relativistic mass greater than their rest mass. Because photons move at the speed of light, they would exhibit relativistic mass as well. In the formulation of general relativity, there's a mathematical object called the stress-energy tensor that acts as the source of the gravitational field in the involved equations, and all forms of energy in a system contribute to it: that includes energy from light, so one could indeed say that light produces a gravitational effect. But this effect is so miniscule that it's barely noticeable: you'd need a RIDICULOUS level of light energy to produce the same effects as a given amount of matter. It wouldn't come into play in anything being discussed here.
Look, here's the thing: the reason I made this mistake in the first place is that general relativity is extremely heady stuff, well beyond the scope of my undergraduate degree. To fully understand its principles, you'd need to have at least a graduate-level background in physics, along with the corresponding higher math principles, or get someone with knowledge of both of those to break things down for you. I don't have either of those--I'm just able to grasp the bare general ideas of it--and I know you don't. This is exactly what I mean by you always trying to utilize topics that you have no real grasp of, which winds up with you attempting to use all sorts of concepts where they don't apply at all.
The problem here is that they told you light is massless, which is true, but then you ASSUME because it's massless it cannot affect atom's which do have mass. That's all you got. Truth is, if you twist it, it can actually trap and freeze atoms thereby exerting a mechanical force on them. Just go teach what you've been told, because insight you do not have.
Where exactly did I say that? Light has the property of momentum, so by definition it is capable of imparting a force on an object. The concept of radiation pressure is a well-understood one...hell, there's been a test version of a "solar sail" that uses the pressure of sunlight to propel a space probe. That's exactly what's going on with the dust motes in that experiment: the photons' angular momentum is imparted to them, which makes them spin. It's not any magical "freezing" or anything.