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  • Almost all astronomers agree on the theory of the Big Bang, that the entire Universe

  • is spreading apart, with distant galaxies speeding away from us in all directions.

  • Run the clock backwards to 13.8 billion years ago, and everything in the Cosmos started

  • out as a single point in space.

  • In an instant, everything expanded outward from that location, forming the energy, atoms

  • and eventually the stars and galaxies we see today.

  • But to call this concept merely a theory is to misjudge the overwhelming amount of evidence.

  • There are separate lines of evidence, each of which independently points towards this

  • as the origin story for our Universe.

  • The first came with the amazing discovery that almost all galaxies are moving away from

  • us.

  • In 1912, Vesto Slipher calculated the speed and direction of "spiral nebulae" by measuring

  • the change in the wavelengths of light coming from them. He realized that most of them were

  • moving away from us.

  • We now know these objects are galaxies, but a century ago astronomers thought these vast

  • collections of stars might actually be within the Milky Way.

  • In 1924, Edwin Hubble figured out that these galaxies are actually outside the Milky Way.

  • He observed a special type of variable star that has a direct relationship between its

  • energy output and the time it takes to pulse in brightness.

  • By finding these variable stars in other galaxies, he was able to calculate how far away they

  • were.

  • Hubble discovered that all these galaxies are outside our own Milky Way, millions of

  • light-years away.

  • So, if these galaxies are far, far away, and moving quickly away from us, this suggests

  • that the entire Universe must have been located in a single point billions of years ago.

  • The second line of evidence came from the abundance of elements we see around us.

  • In the earliest moments after the Big Bang, there was nothing more than hydrogen compressed

  • into a tiny volume, with crazy high heat and pressure.

  • The entire Universe was acting like the core of a star, fusing hydrogen into helium and

  • other elements.

  • This is known as Big Bang Nucleosynthesis. As astronomers look out into the Universe

  • and measure the ratios of hydrogen, helium and other trace elements, they exactly match

  • what you would expect to find if the entire Universe was once a really big star.

  • Line of evidence number 3: cosmic microwave background radiation.

  • In the 1960s, Arno Penzias and Robert Wilson were experimenting with a 6-meter radio telescope,

  • and discovered a background radio emission that was coming from every direction in the

  • sky - day or night.

  • From what they could tell, the entire sky measured a few degrees above absolute zero.

  • Theories predicted that after a Big Bang, there would have been a tremendous release

  • of radiation.

  • And now, billions of years later, this radiation would be moving so fast away from us that

  • the wavelength of this radiation would have been shifted from visible light to the microwave

  • background radiation we see today.

  • The final line of evidence is the formation of galaxies and the large scale structure

  • of the cosmos.

  • About 10,000 years after the Big Bang, the Universe cooled to the point that the gravitational

  • attraction of matter was the dominant form of energy density in the Universe.

  • This mass was able to collect together into the first stars, galaxies and eventually the

  • large scale structures we see across the Universe today.

  • These are known as the 4 pillars of the Big Bang Theory.

  • Four independent lines of evidence that build up one of the most influential and well-supported

  • theories in all of cosmology.

  • But there are more lines of evidence.

  • There are fluctuations in the cosmic microwave background radiation, we don't see any stars

  • older than 13.8 billion years, the discoveries of dark matter and dark energy, along with

  • how the light curves from distant supernovae.

  • So, even though it's a theory, we should regard it the same way that we regard gravity, evolution

  • and general relativity.

  • We have a pretty good idea of what's going on, and we've come up with a good way to understand

  • and explain it.

  • As time progresses we'll come up with more inventive experiments to throw at. We'll refine

  • our understanding and the theory that goes along with it.

  • Most importantly, we can have confidence when talking about what we know about the early

  • stages of our magnificent Universe and why we understand it to be true.

Almost all astronomers agree on the theory of the Big Bang, that the entire Universe

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宇宙大爆炸的證據是什麼? (What Is The Evidence For The Big Bang?)

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    怡蕙 發佈於 2021 年 01 月 14 日
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