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 sopra the past.

Mediante every direction we care onesto observe, we find stars, galaxies, clouds of gas and dust, tenuous plasmas, and radiation spanning the gamut of wavelengths: from radiotrasmittente onesto infrared preciso visible light sicuro modo rays. In nessun caso 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 onesto garantit that it all came from somewhere. If you want to know the answer sicuro the biggest question of all – the question of our cosmic origins – you have to pose the question esatto 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 sicuro simply extrapolate forward in 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 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 pensiero, of per 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 a 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 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 pensiero preciso some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around per solo mass, like the Sun; he applied these results onesto our Solar System with dramatic success. Very quickly, a 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 per 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 mediante 1915: per novel theory of gravity that sought preciso 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 a pointlike mass, which describes a nonrotating black hole.
  2. In 1917, Willem de Sitter found the solution for an empty universe with a cosmological constant, which describes an exponentially expanding universe.
  3. From 1916 sicuro 1921, the Reissner-Nordstrom solution, found independently by four researchers, described the spacetime for a charged, spherically symmetric mass.
  4. Con 1921, Edward Kasner found a solution that described per matter-and-radiation-free universe that’s anisotropic: different per different directions.
  5. In 1922, Alexander Friedmann discovered the solution for an isotropic (same in 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 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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