The Big Bang teaches us that our expanding, cooling universe used to be younger, denser, and hotter con the past.
Con every direction we care puro observe, we find stars, galaxies, clouds of vapore and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radio to infrared preciso visible light onesto gamma rays. Giammai matter where or how we look at the universe, it’s full of matter and energy absolutely everywhere and at all times. And yet, it’s only natural esatto garantit that it all came from somewhere. If you want esatto know the answer to the biggest question of all – the question of our cosmic origins – you have to pose the question onesto the universe itself, and listen onesto what it tells you.
Today, the universe as we see it is expanding, rarifying (getting less dense), and cooling. Although it’s tempting puro simply extrapolate forward durante time, when things will be even larger, less dense, and https://datingranking.net/it/skout-review/ cooler, the laws of physics allow us to extrapolate backward just as easily. Long spillo, the universe was smaller, denser, and hotter. How far back can we take this extrapolation? Mathematically, it’s tempting puro go as far as possible: all the way back puro infinitesimal sizes and infinite densities and temperatures, or what we know as verso singularity. This pensiero, of a singular beginning onesto space, time, and the universe, was long known as the Big Bang.
The modern cosmic picture of our universe’s history begins not with per singularity that we identify with the Big Bang, but rather with per period of cosmic inflation that stretches the universe sicuro enormous scales, with uniform properties and spatial flatness
But physically, when we looked closely enough, we found that the universe told per different story. Here’s how we know the Big Bang isn’t the beginning of the universe anymore.
Countless scientific tests of Einstein’s general theory of relativity have been performed, subjecting the timore to some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around per scapolo mass, like the Sun; he applied these results to our Solar System with dramatic success. Very quickly, verso handful of exact solutions were found thereafter. (Credit: LIGO scientific collaboration, T. Pyle, Caltech/MIT)
Where did all this che from?
Like most stories in science, the origin of the Big Bang has its roots in both theoretical and experimental/observational realms. On the theory side, Einstein put forth his general theory of relativity durante 1915: verso novel theory of gravity that sought onesto overthrow Newton’s theory of universal gravitation. Although Einstein’s theory was far more intricate and complicated, it wasn’t long before the first exact solutions were found.
- Per 1916, Karl Schwarzschild found the solution for verso pointlike mass, which describes verso nonrotating black hole.
- Sopra 1917, Willem de Sitter found the solution for an empty universe with per cosmological constant, which describes an exponentially expanding universe.
- From 1916 sicuro 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for a charged, spherically symmetric mass.
- Con 1921, Edward Kasner found verso solution that described verso matter-and-radiation-free universe that’s anisotropic: different con different directions.
- In 1922, Alexander Friedmann discovered the solution for an isotropic (same durante all directions) and homogeneous (same at all locations) universe, where any and all types of energy, including matter and radiation, were present.
That last one was very compelling for two reasons. One is that it appeared puro describe our universe on the largest scales, where things appear similar, on average, everywhere and in all directions. And two, if you solved the governing equations for this solution – the Friedmann equations – you’d find that the universe it describes cannot be static, but must either expand or contract.