Surprise: the Big Bang isn’t the beginning of the universe anymore

The Big Bang teaches us that our expanding, cooling universe used preciso be younger, denser, and hotter sopra the past.

Con every direction we care esatto observe, we find stars, galaxies, clouds of vapore and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radiotrasmittente preciso infrared sicuro visible light to qualita rays. No 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 endosse 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 preciso pose the question puro the universe itself, and listen sicuro what it tells you.

Today, the universe as we see it is expanding, rarifying (getting less dense), and cooling. Although it’s tempting sicuro simply extrapolate forward sopra time, when things will be even larger, less dense, and cooler, the laws of physics allow us onesto extrapolate backward just as easily. Long ago, 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 a singularity. This idea, of verso singular beginning to space, time, and the universe, was long known as the Big Bang.

The modern cosmic picture of our universe’s history begins not with a singularity that we identify with the Big Bang, but rather with a period of cosmic inflation that stretches the universe to 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 pensiero puro some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around verso scapolo mass, like the Sun; he applied these results esatto our Solar System with dramatic success. Very quickly, per handful of exact solutions were found thereafter. (Credit: LIGO scientific collaboration, Tau. Pyle, Caltech/MIT)

Where did all this che razza di from?

Like most stories durante science, the origin of the Big Bang has its roots durante both theoretical and experimental/observational realms. On the theory side, Einstein put forth his general theory of relativity in 1915: a 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.

  1. Durante 1916, Karl Schwarzschild found the solution for verso pointlike mass, which describes per nonrotating black hole.
  2. In 1917, Willem de Sitter found the solution for an empty universe with per cosmological constant, which describes an exponentially expanding universe.
  3. From 1916 preciso 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for per charged, spherically symmetric mass.
  4. In 1921, Edward Kasner found verso solution that described per matter-and-radiation-free universe that’s anisotropic: different con different directions.
  5. Durante 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 esatto describe our universe on the largest scales, where things appear similar, on average, everywhere and sopra 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.

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