If a distant galaxy were rushing toward our galaxy, he argued, it would move closer to the light waves it was producing, which would decrease the distance between wave crests and shift its color to the blue end of the spectrum. Hubble reasoned that light waves created by galaxies were behaving similarly. Up next, we're going to examine some of that evidence. Today, the universe continues to expand, and astronomers have evidence to prove it. On at least one of those planets, life evolved, some 11 billion years after the big bang started it all. Around some of those stars, gravity pulled together rocks, ice and other materials to form planets. The protogalaxies matured into galaxies, great islands of gas and dust that gave birth to billions of stars. Huge clusters of protogalaxies began to form. These disturbances were just significant enough to cause matter to coalesce. But astronomers now think it was more like a soup, very smooth in density except for a few tiny fluctuations. You might be tempted to picture this young universe as a stew, with clumps of matter floating in thick gravy. The universe continued to expand and thin out. First came electrons and protons, which then combined to form hydrogen and helium atoms. As it did, the temperature dropped to 5,432 degrees Fahrenheit (3,000 degrees Celsius), allowing more stable particles to form. Within roughly 300,000 years, everything held within the singularity had expanded into a seething, opaque sphere of matter and radiation. Because the big crunch is actually a consequence of the big bang, let's start there. In the meantime, let's dive deeper into the big crunch to understand what it is and what it means for the universe. It will be billions of years before we know for sure which camp is right. One camp says the soufflé will fall the other camp says the soufflé will expand forever. Cosmologists are currently engaged in a hot debate. Luckily, the big crunch is not a guarantee. It spells the doom of every galaxy, star and planet that currently exists. Nobody likes a fallen soufflé, and we shouldn't like a universe that behaves like one. Eventually, however, the soufflé cools and begins to collapse. It starts out small, then expands as it heats up.

If the theory holds true, the universe is like a giant soufflé. Then, as gravity pulls on the matter, the universe will begin to contract, falling inward until it has collapsed back into a super-hot, super-dense singularity. One such theory, concerning the future of the universe, is playfully known as the 'big crunch.' According to this theory, the universe will one day stop expanding. They can, however, collect evidence, make educated guesses and establish theories. Because of this, cosmologists can't know with certainty how the universe began or how it will end. The universe is huge compared to a single planet, even a single galaxy, and its timeline is much, much longer. The scale that these scientists work at, of course, is much different. Some astronomers - those who call themselves cosmologists - ask similar questions about the universe. If such a thing were to happen, how long would it take? A hundred years? A thousand? A million? Will it be a hospitable blue ball forever, or will it eventually be consumed by the sun as it swells from a medium-sized yellow star to a red giant? Or perhaps we'll poison our planet, and it will float, cold and desolate, through space. Many of us also wonder about the fate of Earth. Because it's inevitable, we worry about when, where and how it will happen. We see other living things die, and we know it will happen to us. We're all worried about what will happen at the end of our lives.

Whats crunch