So what’s gravity? You know, besides being the reason your fat rolls vibrate when you ride the bus.
Originally, Newton claimed that gravity was an invisible force between any objects with mass(but now we understand that he meant to say energy and momentum because otherwise light wouldn’t be affected, but it is and I’ll get to that later). The story is that an apple fell on his head, but that’s not really what happened, but this is another story for another time.
But Einstein more or less said that it’s not actually a force, but simply a dent in the space-time continuum. If you don’t know what that is, imagine this entire world like a graph. Just like the picture above. See that? That’s the space time continuum being affected by the gravity of Earth. So because of the dent, you can imagine things falling towards it if it’s near it, like it would with a napkin and a coin. But unlike the tissue and napkin, once dented by gravity, the dent never truly reaches ‘equilibrium’ in the edges or even ‘outside.’ Gravity is omni-permeating and affects everything, and so things even light years away are ever so slowly ‘falling’ towards the dent. Of course this doesn’t actually happen because there are other dents in space as well. Gravity affects EVERYTHING and EVERYWHERE. That nebula you see light years away? Yup, it’s affecting you but the force is so minimal that it hardly matters.
Note 1/12/2013 10:19 Central: http://www.physicsforums.com/showthread.php?t=663799
Somebody on the PF forums gave me their defining feature and definition of gravity. Here you go. I won’t be able to argue with this because I don’t know what mass is defined as, so I guess I’ll go into that next.
"Gravity is caused by the rest mass (and a tiny bit by the kinetic energy of a system) and affects particles with relativistic mass. Neither rest mass nor relativistic mass of matter cease to exist at zero temperature."
You might say, “Well then why does gravity affect mass if you say gravity only affects energy and momentum?” This is because of the mass-energy equivalence, which looks something like this, you might’ve seen it before:
Yes, e=mc^2 by Einstein. Of course, this is the incomplete equation. The REAL equation would look something like e=pc^2 + (mc^2)^2. So if energy = mass to a factor of the speed of light and energy equals momentum to a factor of the speed of light, the mass-energy equivalence basically states that anything with mass has energy, but not vice-versa. Light is a great example.
Light is affected by gravity, even though it’s massless. This is because it has momentum. This was noticed during an eclipse when a star behind the sun relative to Earth should not have been visible, because it’s you know, behind the sun. However, we can see that the gravity of the sun bent the light around the sun in its curvature of space-time.
So why is gravity here? What causes gravity? Why just energy and momentum? Truth is, nobody knows. The most common accepted consensus is the space-time continuum explanation, but that still doesn’t explain everything. Some speculate that gravity is composed of massless particles called gravitons. However if this were the case, gravitons would have energy and would thus be affected by their own quantum field ‘gravity’ and ergo gravity’s force would infinitely exponentialize or they would both neutralize out and gravity wouldn’t be a force.
So let’s crash course what we just learned:
- Gravity affects anything with energy and momentum.
- It is a dent in space-time.
- Nobody knows what causes gravity or why it’s here.
- The mass-energy equivalency allows mass to have energy and thus be affected by gravity but not vice versa.
I also have a theory on absolute zero in relations to gravity and I’ll post it here in-case anyone is interested.
If absolute-zero is the theoretical state of a system in which the system reaches 0 Kinetic Energy, then it has no energy nor momentum. If gravity affects things with energy and momentum, does it cease to affect the zero system due to its lack of energy and ergo momentum?
Of course I believe this is impossible to occur on Earth because the Earth is rapidly moving through the space-time continuum and along with everything else in it, so everything on Earth and Earth itself has momentum and thus energy so we will never achieve ‘absolute zero’ on Earth or anywhere else for that matter unless you can create a system in space-time continuum that ISN’T moving, which is completely impossible because according to Relativity, EVERYTHING is moving and nothing is not-moving.
Or am I incorrect in my hypothesis in that absolute zero is only relative to the frame of reference it is in? And by that I mean that it doesn’t have to be not-moving in the universal frame of reference(I know no such thing exists but you probably get the gist of what I’m trying to say), but simply not moving relative to Earth or wherever the system is located?
There’s multiple problems with this but it’s a start. If an absolute zero system were ever to exist I believe it would be a key factor in solving the mystery of gravity. However, there is no experimental way to test this even if absolute zero were impossible because the only way to see if this works is to lift the system and see if it levitates because of the lack of force from gravity, but simply moving the system would give it momentum, thus energy, and thus heat and it will no longer be absolute zero. Or maybe we could make something hold onto the system in mid-air and let go? But according to laws of thermodynamics as long as the crane or whatever’s holding it is holding the system, it will give energy to the system and thus the system will not reach absolute zero.
So I just found out that the above would be wrong because it’s SIGMA (summation) E= mc^2, not KE=mc^2, which is the only thing absolute zero would have minimal value in. So even without KE, there would be other energy, such as energy from the energy-mass equivalence from the mass. Thanks PF members for clearing that up. I’ll still leave it up there incase people want to see how I reached that conclusion.
Blah. My head hurts. More tea.
I’ll explore into mass or energy next, whichever I feel like doing. Or maybe matter. Dunno. Anyways, gonna snooze now. Ciao!