Hypography Science Forums: Roberto - Viewing Profile - Hypography Science Forums

Our present understanding of gravity suggests that it is only a manifestation of spacetime curvature. Mass curves the space around it. The mechanism is unclear, but it happens.

According to General Relativity, a body subject only to gravitation, simply describes a path in the space that corresponds to the shortest distance between two points of spacetime. When there is no body in the neighborhoods, it describes a straight line at constant velocity. When a body happens to be next, the curvature of spacetime makes the shortest path between to points to be distorted and the moving body will simply follow this distortion.

Pretty simple, isn't it? This is equivalent to say that all bodies subject only to gravity travel in geodesics in the spacetime. Matter curves spacetime and distort these geodesics from a straight line to other curves, depending on the distribution of matter.

The only observation is that you cannot travel at the speed of light. Only massless particles can (and in fact, they always do).

What do you mean when you ask if science is valid?

The work of science is to organize the phenomena we see in nature and to use this knowledge to make predictions that can be tested and modify our environment. In science, the questions that are valid are the questions that can be answered. Of course those questions vary with time.

In science, predictions that cannot be tested have no validity or no usefulness. Someday I though about a situation that you can find interesting. Suppose that there are two inhabited identical universes that cannot interact in any way. For science in one of these universes there is no meaning of asking about the existence of the other, because you will never be able to test if it exists or not, although you can ask that question and it has a positive answer.

There can be things that our senses or even our intelligence can never touch, but the aim of science is to understand those which we can. Is it valid? Of course it is. How do you think that the computer you're looking at now was created?

In fact, Everett´s Many Worlds Interpretation of Quantum Mechanics is not really a physical theory, it is an interpretation of QM and not the most popular.

In QM, the mathematics is perfect and all the predictions based on the mathematical theory are confirmed by the experiments, but the interpretation of the mathematics is difficult. The most used interpretation is known as the Copenhagen interpretation, a probabilistic interpretation.
In this interpretation, it is assumed that a system is in a state that is a combination of all possible states it can assume untill someone do a measurement, after what the system choses a state according to certain probabilities. The point is that the system wasn´t in a specific state, it really was in a mixture before the measurement.

Everett´s interpretation says that the system does not chose a state, somehow all the possibilities exist in parallel universes and it just happens that we are following one of the possibilities while copies of us follow ALL the others.

Well, first, it is not a real physical theory at the moment because it cannot be tested. A physical theory needs to make predictions to be tested or else it´s just an idea, not a theory.

Second, the cause that it is not so popular is that it generates more problems than solves (if it really solves any): why we are following exactly this universe? Can we really accept that some choice we make creates whole universes? If there are infinite choices, infinite universes are created instantaneously. Does it make sense?

You must be aware that there are a lot of alternative interpretations of QM. I can cite two at least: Bohmian Mechanics and Sum Over Histories. The only way to decide between them is to work more on it´s differences and try to make experiments to chose among them.

Gravity move at light speed and gravitons are massless. That´s true. Every massless particle travels at the light speed.

Radio waves move at light speed because they´re light. Light is only electromagnetic waves. What you´re taking for "light" in physics we call "visible light". Light is a term used in physics to electromagnetic waves regardless of their frequency. That includes: radio waves, UV rays, microwaves, infrared light, X rays and so on.