Penrose’s discovery that a star of great enough mass undergoing gravitational collapse must form a singularity set fire to Hawking. With Robert Geroch and Penrose, he began to extend ideas about singularities to other physical and mathematical cases. He was certain the discovery had significant implications for the beginning of the universe. This was exhilarating work, with the ‘glorious feeling of having a whole field virtually to ourselves’. Hawking realized that if he reversed the direction of time so that the collapse became an expansion, everything in Penrose’s theory would still hold. If general relativity tells us that any star that collapses beyond a certain point must end in a singularity, then it also tells us that any expanding universe must have begun as a singularity. For this to be true the universe must be like what scientists call a Friedmann model.
Click on the imagem below and catch a glimpse of the Friedmann models of the universe:
Credits: NASA / Chandra X-Ray Observatory
Which model fits our universe?Will the universe collapse some day or go on expanding forever? It depends on how much mass there is in the universe […]. It will take much more mass than we presently observe to close the universe. […]
Penrose’s theory about stars collapsing and becoming singularities only worked with a universe infinite in space that will go on expanding forever, not collapse. Hawking first set out to prove that a universe infinite in space not only would have singularities in black holes but also must have begun as a singularity. He was confident enough by the time he finished his thesis to write: ‘There is a singularity in our past.’
PREDICTING THE DETAILS OF THE UNIVERSE WE LIVE IN, THE THEORY OF EVERYTHING
The calculations necessary to study all the data in the universe are ludicrously far beyond the capacity of any imaginable computer. Hawking points out that although we can solve the equations for the movement of two bodies in Newton’s theory of gravity, we can’t solve them exactly for three bodies, not because Newton’s theory doesn’t work for three bodies but because the maths is too complicated. The real universe, needless to say, has more than three bodies in it.
No começo eu não entendia muito bem como não se é possível tirar conclusões exatas sobre situações e coisas tão recorrentes, tão práticas, cotidianas… tão físicas. Na verdade tinha plena certeza de que era possível: só era preciso tempo e capacidade. Eu até estava certo, só não sabia que o tempo e a capacidade necessários podem, de repente, ser infinitos.
Nor can we predict our health, although we understand the principles that underlie medicine, the principles of chemistry and biology, extremely well. The problem again is that there are too many billions upon billions of details in a real-life system, even when that system is just one human body.
Even with the Theory of Everything in our hands we’d still be a staggeringly long way from predicting everything. Even if the underlying principles are simple and well understood, the way they work out is enormously complicated. ‘A minute to learn, the lifetime of the universe to master’, to paraphrase an advertising slogan. ‘Lifetime of the universe to master’ is a gross understatement.
GEDANKEN, em alemão, “pensamentos”, foi a forma que eu encontrei de, ao mesmo tempo, consolidar e compartilhar o que passa pela minha cabeça. GEDANKEN mostra as pedras nas quais pisei, os líquens que escorreguei, as poças que não achei tão fundas. É uma compilação de ideias fluidas, completas, autoexplicativas e não relacionadas: uma ode a tudo o que me afetou de alguma maneira.
gedanken 