The CMB is not only one of the major pieces of evidence for the Big Bang (it's a baby picture of the universe…what else could you ask for?), but it's also a window to even earlier times. But the universe is older and colder, and those high-energy gamma rays are now listless microwaves, creating a background permeating the cosmos - a cosmic microwave background, or CMB, if you will. This is a plasma, and at one time, the entire universe lived like this.įast-forward to the present day, and the leftover light from the era, when the universe cooled and expanded just enough to let the first atoms form, continues to wash over us right now. It's so dense that every time a nucleus ropes in an electron, a careless high-energy photon slams into it, ripping the electron away. Push back more than 13 billion years, when the universe was just one-thousandth of its current extent, and the matter that would one day make up entire galaxies is crammed together so tightly that atoms can't even form. The birth of the Dark Energy Age might not seem that dramatic, but the further back you go in time - and the smaller you make the universe - the stranger it gets. (Side note: The dark energy takeover happened at about the same time our solar system was getting its stuff together, and at the time, the universe was about half its present size.) And by virtue of its density, that matter was the ruler of the roost, overwhelming dark energy, which was just a background wimp rather than the powerhouse it is now. But a few billion years ago, the universe was smaller, and all the matter was crammed more tightly together. All this stuff behaves differently at different densities, so when the universe was smaller, one kind of thing might dominate over another, and the physical behaviors of that thing would drive whatever was going on in the universe.įor example, nowadays, the universe is mostly dark energy (whatever that is), and its behavior is ruling the universe - in this case, driving a period of accelerated expansion. The universe is made of lots of kinds of stuff: hydrogen, helium, aardvarks, dark matter, gristle, photons, Ferris wheels, neutrinos, etc. Here's the gist: The story of the past 14-ish billion years is a story of density. Īnd if you notice that, every day, the universe is getting bigger, you can make a tremendous leap of logic to come to the conclusion that, long ago, the universe was … smaller? Maybe? I guess? Like any good scientist, as soon as you cook up this kind of ridiculous, preposterous concept, you start thinking through what the consequences would be and how you might test it - I know, radical notions. And it's not just on local scales the whole shindig changes character one day to the next. The universe today is different from how it was yesterday, and it will be different tomorrow. At least that's what people thought.īut it's not. Check again in a month? Yup, the same universe. Yeah, stars may blow up or galaxies may collide, but on the whole, the universe from last week looks pretty much like the universe today. For millennia, the default assumption (can you blame anyone?) was that, while things change here on Earth, up in the distant heavens, stuff just sort of… is. The evidence starts with Edwin Hubble's note that every galaxy is, on average, flying away from every other galaxy. And what was left after decades of evidence? Here's a hint: It's big. Any new observation is the scientific Thunderdome two theories may enter, but only one can leave. You know, the actual universe that we're trying to understand. Why? Because whoever takes down a major scientific paradigm gets a free trip to Stockholm.Īnd at the end of it all, there's the evidence. Since the idea was first cooked up, the Big Bang theory has survived decades of scientists fighting, scratching, backstabbing, criticizing, undermining, bickering, arguing and even name-calling, all in an attempt to crush their rivals and prove that their pet alternatives were superior.
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