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

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

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

In every direction we care sicuro observe, we find stars, galaxies, clouds of corpo gassoso and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radio puro infrared esatto visible light puro 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 assure that it all came from somewhere. If you want puro know the answer to the biggest question of all – the question of our cosmic origins – you have sicuro pose the question puro the universe itself, and listen puro 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 per 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 onesto 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 ispirazione, of verso 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 a singularity that we identify with the Big Bang, but rather with verso 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 ispirazione to some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around verso single mass, like the Sun; he applied these results to 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?

Like most stories sopra science, the origin of the Big Bang has its roots mediante 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 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. Mediante 1916, Karl Schwarzschild found the solution for verso pointlike mass, which describes a nonrotating black hole.
  2. Mediante 1917, Willem de Sitter found the solution for an empty universe with per cosmological constant, which describes an exponentially expanding universe.
  3. From 1916 esatto 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for per charged, spherically symmetric mass.
  4. Mediante 1921, Edward Kasner found verso solution that described verso matter-and-radiation-free universe that’s anisotropic: different mediante different directions.
  5. Sopra 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 con 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.