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What is the world? What is existence?
There can be several answers for these questions, a philosophical one, a scientific one, a religious one, and so on.
Science can give only a limited answer for this kind of questions. But I believe that physics will provide at least one possible description of the world someday. Today I'd like to explain about my graduate research - astrophysics.
It has been long believed that gravitation is an attractive force which attracts masses each other. But in the theory of general relativity, which was introduced by Albert Einstein, gravitation is explained as a "curve" of space and time. According to this theory, when there is a mass (or equivalently energy) at some point, space and time around it are curved by the presence of it. For example, the space around the Sun is curved by the mass of the Sun and the Earth goes "straight" along this curve. We observe this as a motion of rotation, and it appears as if it were caused by their attraction.
This theory also showed us the possibility that space and time expand or contract. And later, the expansion of the universe was discovered actually.
This amazing fact also implies that the ancient universe was smaller than it is today. At the very beginning of the universe, everything including us was being packed in one point. Recent researches also have shown the possibility that in the very early universe and the current universe, the expansion was/is accelerating. This might be explained by the effect of "dark energy" which is an unknown constituent which occupies the considerable part of the universe. In fact, more than 95 percent of the components of the universe are unknown ones, "dark energy" and "dark matter".
There can be several answers for these questions, a philosophical one, a scientific one, a religious one, and so on.
Science can give only a limited answer for this kind of questions. But I believe that physics will provide at least one possible description of the world someday. Today I'd like to explain about my graduate research - astrophysics.
It has been long believed that gravitation is an attractive force which attracts masses each other. But in the theory of general relativity, which was introduced by Albert Einstein, gravitation is explained as a "curve" of space and time. According to this theory, when there is a mass (or equivalently energy) at some point, space and time around it are curved by the presence of it. For example, the space around the Sun is curved by the mass of the Sun and the Earth goes "straight" along this curve. We observe this as a motion of rotation, and it appears as if it were caused by their attraction.
This theory also showed us the possibility that space and time expand or contract. And later, the expansion of the universe was discovered actually.
This amazing fact also implies that the ancient universe was smaller than it is today. At the very beginning of the universe, everything including us was being packed in one point. Recent researches also have shown the possibility that in the very early universe and the current universe, the expansion was/is accelerating. This might be explained by the effect of "dark energy" which is an unknown constituent which occupies the considerable part of the universe. In fact, more than 95 percent of the components of the universe are unknown ones, "dark energy" and "dark matter".
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Science can give only a limited answer for these kind of questions.
It has long been believed that gravitation is an attractive force which attracts masses to each other.
According to this theory, when there is a mass (or equivalently energy) at some point, space and time around it are curved by the presence of it.
And later, the expansion of the universe was discovered to be actually true.
At the very beginning of the universe, everything including us was being packed into one point.
Recent researches also have shown the possibility that in the very early universe and the current universe, the expansion was/is accelerating. (This sentence doesn't really need the pluralization of "researches"... It would sound better starting with "Recent research has also show the possibility....")
In fact, more than 95 percent of the components of the universe are unknown ones, such as "dark energy" and "dark matter".
Thank you for your corrections and detailed explanation!
Do you do any research?
But in the theory of general relativity, which was introduced by Albert Einstein, gravitation is explained as the curvature of space and time. <Maybe it would be better to write "the curvature of space-time." In any case, in differential geometry--the mathematical foundations of classical GR--"curve" and "curvature" are different concepts, while at the same time they are both widely used.>
<"equivalently energy" is correct, as you are not referring to any equivalent mass of anything, but to the fact that the very moment you introduce Lorentz invariance, mass and energy become one and the same thing. Although I must warn you the modern concept of mass is not used in that sense anymore--see for example Taylor-Wheeler, Spacetime physics (http://www.compadre.org/student/items/detail.cfm?ID=519)--, but we refer only to the zero-th component of 4-momentum as "energy," while mass is just the parameter that in the old literature about Classical Field Theory was known as "rest mass.">
This theory also showed us the possibility that space-time expands or contracts. <Or even better: "space expands or contracts with time."Time per se does not contract, it's actually the space foliations that do. I know you mean: in a Robertson-Walker metric it's the dilation factor R(t) which takes care of that; but then again, that's no time contraction or expansion, but only relative contraction or expansion of the spacial part of the metric with respect to the time contribution.>
In fact, more than 95 percent of the mass of the universe is of unknown origin, "dark energy" and "dark matter". <There's no other possibility besides DE and DM is there?> <And it's not the components (you unwillingly seem to suggest particle types, although exotic matter could be involved) but the mass deficit what you mean really.>
It's great to meet a cosmologist around here.
If you have any questions don't hesitate to ask me.
Thank you for your very detailed explanations and encouraging word!
I deeply appreciate it.
> curvature
> space-time
I wanted to make this article intelligible even to those who doesn't have knowledge of physics, so I avoided using such scientific terms as much as possible. I also thought that the more such technical terms I include, the less likely I can get corrections ha ha.
By the way, you seem to have a thorough knowledge of modern physics.
Are you a physicist?
Anyway.
I already sent you a message answering your questions. If you have any further questions I'll be glad to answer, but I have the feeling you could teach me much more than I could teach you.
Take care. And keep an eye on the universe my friend.