Jun 3 2012: The expansion actually affects all space-time, whether in galaxies or not. One simplified way to see it is like a force pushing objects from one another, which would be proportional to the distance between them. On a galaxy scale, it is a negligible force. It starts becoming strong enough when we are at scales close to the hole universe's.
Apr 28 2012: There is just one thing in your reply that I probably don't understand well. You say that gravity could be instantaneous ? Wouldn't that be in contradiction to Einstein's theory of relativity ?
Because what I understood is this. Acceleration is just in fact the consequence of the curvature of space time. Particles, in space time, go in straight lines. And particles with mass themselves make curvature. However, in all of this, a change of curvature cannot propagate at a higher speed than light. Am I wrong ?
Apr 28 2012: The Pauli Exclusion Principle only applies to fermions. For example, electrons are fermions.
However, many particles are not fermions. The latter are called bosons.
For example, photons are such particles. This means that you can have two photons with the same state, which is not possible for the electron.But being in a certain state is a bit more complex than just "being somehere". It also means having the same spin, and probably other things that I don't recall perfectly.
However, you also need to realize what "being in a place" means in quantum theory. Indeed, a particle is no longer a single point, but a "cloud", and the "cloud" only describes the probability, "if you observe the particle", to find it in a point of space. Quantum theory describes the motion of this cloud in a given potential, just like Newtonian physics describes the motion of a point particle considering the forces exerted on it.
So if you ask the questions : can two clouds overlap ? Sure they can. However, one will probably be more dense at a different place than the other.
Apr 28 2012: This is not true of most great thinkers. Einstein himself said that he would not have "found the answer" (special relativity), if he had not read the books of great thinkers that preceded him : Kant, Maxwell of course, Newton, and also a few philosophers.
Laforgue (Field Medal), defends the idea that mathematicians are a community that have traditions. He reminds people of the importance to have mentors, and not to be isolated from the community. People that try to find something new but who do not interact with the working community usually end up making basic errors just because they do not have some of the otherwise well known knowledge.
However, I do defend that knowledge is not sufficient : thinking is also necessary to make the next step possible.
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A reply on Talk: Seth Shostak: ET is (probably) out there -- get ready
A reply on Talk: Just how small is an atom?
Because what I understood is this. Acceleration is just in fact the consequence of the curvature of space time. Particles, in space time, go in straight lines. And particles with mass themselves make curvature. However, in all of this, a change of curvature cannot propagate at a higher speed than light. Am I wrong ?
A reply on Talk: Just how small is an atom?
However, many particles are not fermions. The latter are called bosons.
For example, photons are such particles. This means that you can have two photons with the same state, which is not possible for the electron.But being in a certain state is a bit more complex than just "being somehere". It also means having the same spin, and probably other things that I don't recall perfectly.
However, you also need to realize what "being in a place" means in quantum theory. Indeed, a particle is no longer a single point, but a "cloud", and the "cloud" only describes the probability, "if you observe the particle", to find it in a point of space. Quantum theory describes the motion of this cloud in a given potential, just like Newtonian physics describes the motion of a point particle considering the forces exerted on it.
So if you ask the questions : can two clouds overlap ? Sure they can. However, one will probably be more dense at a different place than the other.
A reply on Talk: Just how small is an atom?
Laforgue (Field Medal), defends the idea that mathematicians are a community that have traditions. He reminds people of the importance to have mentors, and not to be isolated from the community. People that try to find something new but who do not interact with the working community usually end up making basic errors just because they do not have some of the otherwise well known knowledge.
However, I do defend that knowledge is not sufficient : thinking is also necessary to make the next step possible.