Posted: Mon May 24, 2010 2:07 pm
Well, the Big Bang theory is just a theory, that's true. This is because it's impossible to prove. A theory just holds as long as there are no facts disproving it. However, with the BBT it's possible to explain many things that couldn't be explained otherwise. One of the strong indications that it could be true is the existance of the cosmic microwave background radiation. This clearly states that the energy density once was as high that light couldn't pass space without being absorbed and reemitted endlessly. The universe was optically dense and that phase only ended about 300000 years after the Big Bang when the universe had expanded sufficiently.
Of course, the BBT doesn't say anything about what was there before. But it also doesn't say the Big Bang came from nothing. It just states that all energy of the universe once was bound in a spot without dimensions. When the Big Bang happened, the expanding energy created the spatial dimensions, as well as time itself. And even if it conflicts with our intuitive understanding that time can't have a beginning or an end, it's a logical explanation.
From my view, the only question is: Where did the energy come from? Energy, in a certain sense, is the true magic of everything. Nothing would exist without it (not even matter), it can't be used up or destoyed (in fact, energy always is being converted) and it seems that it was already there when everything began. And after all, nobody can explain what energy really is.
Thinking about what was there before the Big Bang is highly speculative since we can't obtain any information about it. There are theories, especially in the context of quantum physics (as Ramses has mentioned already), but they're rather providing possibilities than explanations.
@Ramses: First of all, that object with the highest known red shift is not a star (stars would be too faint to see them at that distance), but a Gamma Ray Burst. The fact that it happened about 600 million years after the Big Bang tells us that it is very far away (almost at the outer boundary of the universe), because when the universe expanded during the following 13.1 billion years, the object moved away with it. The distance to the GRB in fact is 13.1 billion lightyears and thus it took light 13.1 billion years to reach us. Nobody knows where the center of the univserse is located, so it's hard to talk about objects on the other side of it. However, we should be able to see any object in space if it is bright enough (regardless in what direction it moves), since speeds have to be added relativistically. The total velocity when adding up two velocities v1 and v2 would then be: (v1 + v2) / 1 + ((v1 * v2) / c^2), where c is the speed of light. So even if v1 and v2 are equal to c, the total velocity never exceeds c.
There are gravitational effects in the universe, of course. But keep in mind the incredible impulse caused by the Big Bang. Gravity weakens with growing distance. On the other hand, the impulse of movement wears off over the time. In fact, it's been one of the big open questions of the past decades whether the universe will expand in all eternity or whether gravitational forces will once win over expansion and the whole universe will pull itself together again. Even a third possibility has been discussed: Expansion will continue and wear off in the same moment when every object is too far away from each other for gravitaional effects. However, the question seems to be answered since scientists discovered that the Hubble constant is growing over the time. This means that the expansion of the universe is accelerating - despite the effect of gravitation. Nobody knows why it is like that, but to handle this (and believe it or not - this truely is the ONLY reason!), scientists have postulated the Dark Energy. We know there's a force that's responsible for the acceleration of the expansion of the universe. And since we can neither see nor measure it, we call it Dark Energy.
It's the same with Dark Matter by the way. Dark Matter was postulated because stars would normally be ejected from our Milky Way if they rotated around it with the speed they do. The only explanation why they don't do so is that there must be stronger gravitation and thus more matter causing it. But once again: Since we can neither see nor measure it, we call it Dark Matter.
@Ronny: It's legitimate to doubt any theory, of course. But one has to give sound reasons to prove something wrong cause otherwise it'll just bring discredit to anyone doing so.
Of course, the BBT doesn't say anything about what was there before. But it also doesn't say the Big Bang came from nothing. It just states that all energy of the universe once was bound in a spot without dimensions. When the Big Bang happened, the expanding energy created the spatial dimensions, as well as time itself. And even if it conflicts with our intuitive understanding that time can't have a beginning or an end, it's a logical explanation.
From my view, the only question is: Where did the energy come from? Energy, in a certain sense, is the true magic of everything. Nothing would exist without it (not even matter), it can't be used up or destoyed (in fact, energy always is being converted) and it seems that it was already there when everything began. And after all, nobody can explain what energy really is.
Thinking about what was there before the Big Bang is highly speculative since we can't obtain any information about it. There are theories, especially in the context of quantum physics (as Ramses has mentioned already), but they're rather providing possibilities than explanations.
@Ramses: First of all, that object with the highest known red shift is not a star (stars would be too faint to see them at that distance), but a Gamma Ray Burst. The fact that it happened about 600 million years after the Big Bang tells us that it is very far away (almost at the outer boundary of the universe), because when the universe expanded during the following 13.1 billion years, the object moved away with it. The distance to the GRB in fact is 13.1 billion lightyears and thus it took light 13.1 billion years to reach us. Nobody knows where the center of the univserse is located, so it's hard to talk about objects on the other side of it. However, we should be able to see any object in space if it is bright enough (regardless in what direction it moves), since speeds have to be added relativistically. The total velocity when adding up two velocities v1 and v2 would then be: (v1 + v2) / 1 + ((v1 * v2) / c^2), where c is the speed of light. So even if v1 and v2 are equal to c, the total velocity never exceeds c.
There are gravitational effects in the universe, of course. But keep in mind the incredible impulse caused by the Big Bang. Gravity weakens with growing distance. On the other hand, the impulse of movement wears off over the time. In fact, it's been one of the big open questions of the past decades whether the universe will expand in all eternity or whether gravitational forces will once win over expansion and the whole universe will pull itself together again. Even a third possibility has been discussed: Expansion will continue and wear off in the same moment when every object is too far away from each other for gravitaional effects. However, the question seems to be answered since scientists discovered that the Hubble constant is growing over the time. This means that the expansion of the universe is accelerating - despite the effect of gravitation. Nobody knows why it is like that, but to handle this (and believe it or not - this truely is the ONLY reason!), scientists have postulated the Dark Energy. We know there's a force that's responsible for the acceleration of the expansion of the universe. And since we can neither see nor measure it, we call it Dark Energy.
It's the same with Dark Matter by the way. Dark Matter was postulated because stars would normally be ejected from our Milky Way if they rotated around it with the speed they do. The only explanation why they don't do so is that there must be stronger gravitation and thus more matter causing it. But once again: Since we can neither see nor measure it, we call it Dark Matter.
@Ronny: It's legitimate to doubt any theory, of course. But one has to give sound reasons to prove something wrong cause otherwise it'll just bring discredit to anyone doing so.
