Just so everyone knows, I dont know very much about physics. I just have a very sincere interest in learning as much as I can. So forgive me if my question is foolish. I have heard many different thoughts on what space is made of. Some say its simply empty, some say its not. What im wondering is if its empty, then how does energy travel? The thought that crossed my mind, which makes me ask that, is if there is simply nothing in space, then wouldnt light lose momentum as its travels because it has nothing to carry it?
Space is essentially empty. That's if you ignore (a) the odd particle here and there, and (b) quantum fluctuations of the vacuum (which are a complicated prediction of quantum field theories that needn't concern you too much). Energy doesn't travel unless something carries it. Maybe you're thinking of light, which carries energy. Light doesn't need a substance to carry it. Particles of light (photons) can travel through a vacuum just like any other kind of particle. It's the other way around. Newton said that an object will move at constant speed in a straight line forever unless it is acted on by a force of some kind. If you launch a spaceship out in space, it will keep going forever unless something hits it and slows it down. If nothing hits it, it won't lose momentum. The same applies to light.
I see...then what stops the Earth, and every other planet from being flung out into space? Of everything in Physics, that makes the least sense to me. One would think that we would succumb to centrifugal force. Especially the planets further away from the Sun, with more mass than the Earth. It just seems that gravity goes against what Newton said. I apologize if my questions seem infantile. I suppose im just trying to understand lol.
The Sun's gravity is constantly pulling the Earth towards the Sun. If it didn't do that, then the Earth wouldn't orbit - it would fly off into space in a straight line and keep going forever. Centrifugal forces are a confusing concept. In a sense, they don't really exist at all. There are no forces pushing outwards on things that travel in circles. In fact, there must always be a net force towards the centre on anything travelling in a circle. That's the force that keeps it moving in a circle rather than having it fly off in a straight line. The distance at which a planet orbits the sun doesn't depend at all on the mass of the planet. It only depends on the speed the planet is going around the sun. How so? What's your understanding of what Newton said?
Gravity. Not really, gravity is the force that stops the Earth (or whatever) travelling in a straight line. If it weren't for gravity we'd keep going at a tangent (not directly outwards) due to the speed of travel and if it weren't for our speed we'd be pulled in toward the Sun. Edit: meh, James R got there first...
While we are on the topic of "energy," what is it? From what I understand, it really isn't "anything" but just a consequence of mathematics... at least when I look at equations like \(\frac{1}{2}mv^2\). Atomic bombs make me think differently...
Ok my understanding of Centrifugal force is that as an object orbits around a central body there is an outward force exerted on the orbiting object. And the force exerted on that object is determined by the distance from the central object and the mass of the orbiting object. The further away the greater the force, and the more mass, more force. Now if there is no outward force exerted, and there is a net force going inward then wouldnt each planet have an orbit which gradually grows closer to the central object? And since it doesnt then wouldnt that mean that there is an outward push? One outward push from the Sun, keeping the planets from drawing closer, and the second being from the inner and outer belts in our solar system, keeping the planets from drifting outwards? Now please do not mistake my questions for debate, I assure you if I dont ask you guys these questions then they will just rattle around until they are answered lol. I am just trying to use critical thinking. Oh and are there any published findings which describe the Mathematics that were used to come to the conclusions that you guys have learned?
Centrifugal force is a false force.. it doesn't exist. It appears to exist when you're in a car, for example, traveling in a circle. Your car is constantly accelerating towards the center yet the objects inside are trying to travel tangent to the circle. Hence, it looks like they are "flying outward."
Dywyddyr stated: "Not really, gravity is the force that stops the Earth (or whatever) travelling in a straight line. If it weren't for gravity we'd keep going at a tangent (not directly outwards) due to the speed of travel and if it weren't for our speed we'd be pulled in toward the Sun." Ok maybe im perceiving what you are saying here. The image it creates in my mind is that of a funnel with the Sun being at the center. Which would mean that gravity is simply a combination of two factors...the depression created by the mass of the sun in the center of our solar system, which would draw us in...and the speed at which the Earth orbits around the Sun, which keeps us away from the Sun. And the two forces combined keeps us on the Earth. Is that right?[/QUOTE]
baptizo1403: No. Objects accelerate in the direction of the net force on them. Orbiting objects are accelerating towards the centre of rotation, not away from it. The object "wants" to go in a straight line. You need a force to turn it towards the central object. Correct. The further away, the less the force. More mass does mean more force, though. No, because the planet's speed keeps it in orbit, rather than falling directly towards the sun. (It's the same when the space shuttle orbits the Earth. It's being pulled down by Earth's gravity all the time, but it doesn't need to continuously fire its engines to stop falling to Earth.) If there was an outwards push, the planets would move outwards. Proofs can be found in any first-year university level physics textbook. What keeps us on the Earth is the Earth's gravity pulling us towards the ground. The Sun's gravity makes us orbit the sun along with the rest of the Earth. Other than that, your picture isn't too bad. Absane: Energy is a property that a physical system has, and it comes in many different forms. The usefulness of energy is that it is often conserved while other things about the system change. So, in one sense, energy is just a useful accounting system. It is not a good idea to think of it as some kind of substance.
Ok so if the picture I have is not inaccurate, and there is a depression created by the Sun, naturally trying to draw the planets towards the Sun, then is there a multi dimensional fabric of space, so to speak, like the surface in the funnel?
The "funnel" picture is one from Einstein's theory of gravity - general relativity. In that theory, gravity is not a force at all, unlike in Newton's model of gravity. In Einstein's picture, planets orbit the sun not because they have a force on them, but because in doing so they are following the curvature of the spacetime they find themselves in, which is created by the sun's mass. Einstein's theory describes space and time together as a 4-dimensional thing - spacetime - with 3 space dimensions and 1 time dimension. The "funnel" picture is inaccurate in that it tries to picture the 4-dimensional surface of spacetime in 3 dimensions. Spacetime is not quite like that, but the analogy works ok for some purposes.
I see. Well I think I have the best understanding of it that ill be able to have without enlisting in school lol. But I really do appreciate you answering my questions. Please Register or Log in to view the hidden image!
I have been thinking more about what you said, and I do have another question lol. But now its about 4th dimensional space time. It was stated that the funnel picture is not entirely accurate because it is taking 4th dimensional spacetime and putting into a 3 dimensional object. So my question is, is spacetime a matter of disturbance rather than an actual substance or anything measurable?
Photons/light carry no matter The only things that can travel light spead must have no matter. Anything with matter can not travel light speed, period. Thus, your question about space being empty doesn't really hit the point, because light is empty.
A more correct way to say this would be objects with mass cannot travel at or above the speed of light. The photon is certainly massless, but that doesn't mean it's "empty," it does have momentum that's not zero.
