The Big Bang teaches us that our expanding, cooling universe used onesto be younger, denser, and hotter sopra the past.
Sopra every direction we care esatto observe, we find stars, galaxies, clouds of gas and dust, tenuous plasmas, and datingranking.net/it/talkwithstranger-review radiation spanning the gamut of wavelengths: from radiotrasmittente preciso infrared onesto visible light preciso varieta rays. Per niente 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 esatto garantit that it all came from somewhere. If you want esatto know the answer sicuro the biggest question of all – the question of our cosmic origins – you have onesto pose the question to the universe itself, and listen esatto what it tells you.
Today, the universe as we see it is expanding, rarifying (getting less dense), and cooling. Although it’s tempting preciso simply extrapolate forward durante time, when things will be even larger, less dense, and cooler, the laws of physics allow us onesto 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 preciso go as far as possible: all the way back sicuro infinitesimal sizes and infinite densities and temperatures, or what we know as per singularity. This timore, 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 verso singularity that we identify with the Big Bang, but rather with verso period of cosmic inflation that stretches the universe esatto enormous scales, with uniform properties and spatial flatness
But physically, when we looked closely enough, we found that the universe told a 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 intenzione esatto some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around verso celibe mass, like the Sun; he applied these results sicuro 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 ad esempio from?
Like most stories sopra science, the origin of the Big Bang has its roots per both theoretical and experimental/observational realms. On the theory side, Einstein put forth his general theory of relativity durante 1915: a novel theory of gravity that sought puro 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.
- Mediante 1916, Karl Schwarzschild found the solution for verso pointlike mass, which describes a nonrotating black hole.
- Durante 1917, Willem de Sitter found the solution for an empty universe with a cosmological constant, which describes an exponentially expanding universe.
- From 1916 to 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for a charged, spherically symmetric mass.
- Durante 1921, Edward Kasner found per solution that described verso matter-and-radiation-free universe that’s anisotropic: different in different directions.
- In 1922, Alexander Friedmann discovered the solution for an isotropic (same sopra 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 mediante 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.