The Big Bang teaches us that our expanding, cooling universe used preciso be younger, denser, and hotter in the past.
Con every direction we care preciso observe, we find stars, galaxies, clouds of corpo gassoso and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radiotrasmittente puro infrared esatto visible light puro qualita rays. Mai matter where or how we aspetto at the universe, it’s full of matter and energy absolutely everywhere and at all times. And yet, it’s only natural sicuro assume that it all came from somewhere. If you want puro know the answer sicuro the biggest question of all – the question of our cosmic origins – you have sicuro pose the question sicuro the universe itself, and listen to 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 sopra time, when things will be even larger, less dense, and 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 esatto go as far as possible: all the way back onesto infinitesimal sizes and infinite densities and temperatures, or what we know as per singularity. This preoccupazione, of a singular beginning preciso 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 a period of cosmic inflation that stretches the universe preciso enormous scales, with uniform properties and spatial flatness
But physically, when we looked closely enough, we found that the universe told verso 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 esatto some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around a single mass, like the Sun; he applied these results sicuro our Solar System with dramatic success. Very quickly, per handful of exact solutions were found thereafter. (Credit: LIGO scientific collaboration, T. Pyle, Caltech/MIT)
Where did all this come from sugardaddymeet?
Like most stories in science, the origin of the Big Bang has its roots sopra both theoretical and experimental/observational realms. On the theory side, Einstein put forth his general theory of relativity sopra 1915: per novel theory of gravity that sought sicuro 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 per nonrotating black hole.
- Mediante 1917, Willem de Sitter found the solution for an empty universe with per cosmological constant, which describes an exponentially expanding universe.
- From 1916 onesto 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for verso charged, spherically symmetric mass.
- Mediante 1921, Edward Kasner found verso solution that described per matter-and-radiation-free universe that’s anisotropic: different durante different directions.
- Sopra 1922, Alexander Friedmann discovered the solution for an isotropic (same con 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 sicuro describe our universe on the largest scales, where things appear similar, on average, everywhere and per 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.
