Genesis
Timeline
In the beginning, there was the Big Bang. We do not yet know what came before the Big Bang. The initial explosion and expansion of our universe occurred about 12 to 15 billion years ago. This release of an incredible amount of energy cooled and expanded over billions of years, eventually coalescing into the matter that makes up the atoms and molecules of our bodies, our world, our sun, our solar system, our galaxy, and all the galaxies of the universe.
The universe continues to expand, and the latest research shows that this expansion is accelerating. This means that the underlying space is expanding, not that objects such as galaxies, planets, and people are expanding. The space which we occupy is expanding slightly, but gravity and molecular attraction are much stronger on a local scale than the current expansion of the universe, and thus each person, planet, star, galaxy, and even cluster of galaxies remains whole. Far away galaxies, however, are receding from us. We do not yet know if the universe is finite or infinite, or if the expansion will continue to accelerate or not.
The Earth formed about 4.5 billion years ago from the disk of matter spinning around the Sun, which formed about half a billion years earlier from swirling clouds of gas in space in the outer arms of our galaxy, the Milky Way. The matter forming the earth was a combination of dust, ice, rock, and gas. As the Earth grew larger, the individual pieces of matter were initially crushed by gravity, then melted under the intense heat and pressure inside what grew to a planet-sized body. Heavier elements such as iron sank to the center, while the lightest constituents such as water and nitrogen rose to the surface. At around 4.1 billion years ago, the surface of the molten earth cooled down enough to become solid land.
Theory & Evidence
As we know, the first event in our known universe was the Big Bang. For our universe, the Big Bang was the beginning of not only space but time as well. Some hypotheses about what happened before include repeated cycles of Big Bangs. Other hypotheses assume that universes can create daughter universes, or that the universe is a multiverse. Still others posit that it is mathematically possible that the universe just began, starting from absolutely nothing. We have not yet figured out ways to test these hypotheses, but maybe in the future we will be able to explore these issues more thoroughly.
However, the theory that there was a Big Bang itself, that the universe is expanding, and many of the actual mechanics of the Big Bang have been thoroughly tested in many different ways. Unlike religious theories of the beginning of existence, which are based on the writings of men hundreds or thousands of years ago, the Big Bang theory was only proposed in 1927, by Catholic priest Georges Lemaître. (The name “Big Bang” wasn’t coined until its use in a 1949 BBC radio show by one of the theory’s detractors, British astronomer Fred Hoyle.) The initial concept that the universe was expanding came as a surprise to many scientists. But, just like any good detective, you have to go where the evidence leads you.
The fleshing out of the Big Bang theory started from the evidence that the universe is expanding, and worked backwards to the conclusion that the universe must have started as an enormously dense, extremely hot and energetic, very small point, sometimes called a singularity. This point exploded out into what has become our universe, with the energy coalescing into matter that gravitated together to form stars and galaxies. Some of the major pieces of evidence supporting the Big Bang Theory are listed below, along with one of the failed hypotheses that attempted to explain the universe without a big bang.
Hubble’s Law
In 1929 Edwin Hubble and Milton Humason put forth what is now known as Hubble’s law. The law explains the redshift in the light arriving from distant stars. This redshift is similar to the well-known Doppler Effect, where an approaching train or ambulance has a higher-pitched sound than a receding one. Sound from a receding object like a train is stretched out into longer wavelengths and lower frequencies. Similarly, light from a receding star is stretched out into the longer wavelengths and lower frequencies of the red side of the spectrum. What Hubble’s Law states is that the redshift in light observable from faraway stars and galaxies is proportional to the distance of the object from the earth. This makes sense if the universe is expanding in all directions, because something twice as far away will be receding twice as fast. (Picture holding a long rubber band, with a pen mark on it one inch away from your hand and another mark two inches away. Now stretch it to twice its length. The closer mark moved slower, only one more inch, while the farther mark moved two inches, twice as fast.) Hubble’s Law showed cosmologists the true size and expansion of the universe, and led scientists to work backwards to the theory of a Big Bang.
Olbers’ Paradox
Olbers’ paradox can be most simply stated by saying, “Why is the night sky dark?” With infinite size, or even just extremely large size, every single point in the night sky should contain a star, and even though that star might be very distant, it should still give us light. So why isn’t the night sky as bright as the sun? The answer lies in the Big Bang, which gives two reasons why the sky is mostly dark. First, the universe is expanding, which will take faraway stars out of our “observable universe” so that no light from them will reach us. The expansion of the universe is pulling them away from us faster than their light is moving. (Yes, no things can move faster than the speed of light, but the expansion of the universe itself can be faster than light.) Second, the universe is not infinitely old, which means that some stars are young enough that their light hasn’t yet had a chance to reach us. Both limited age and expansion support the Big Bang theory.
Homogeneity/Isotropy (Sameness)
The Big Bang theory says that all of the part of the universe we can observe was compressed into an extremely small point back at the time of the Big Bang. Since everything was compressed into the same spot and arose from the same process, we should expect that the universe should be homogeneous, that is, it should look roughly the same in all directions. The homogeneousness, or isotropy, of the universe has been tested, and the universe has been shown to be isotropic on a scale as fine as 1 part in 100,000.
Cosmic Microwave Background Radiation
In the 1940s, scientists predicted that the heat of the early stages of the Big Bang would have left an observable amount of background radiation in the form of microwaves. Equipment was not sophisticated to test this hypothesis until the 1960s, when evidence of the background radiation was detected. Further data regarding the specific nature and pattern of the background radiation was found in the 1990s, and again it matched up with the predictions of the Big Bang theory.
Failure of the Tired Light Hypothesis
The “tired light” hypothesis states that light from distant stars can be redshifted by a gradual energy loss from the travel over such long distances, possibly slowed down by the fabric of space or something like that. However, this hypothesis has been disproved several ways. First, there isn’t any way to change the energy of a photon without altering its momentum as well. Any change in momentum would cause blurring of distant objects, and as we can tell from the views of distant stars and galaxies, this does not occur.
Second, the Big Bang predicts that light from distant events will arrive with time dilation. (What that means is that some objects are so far away that a two-week flash of light might appear to take three weeks from the earth, since by the end of the two weeks the source of the flash has moved the distance that light would take a week to travel.) With supernovas, we have a good idea of how long the event should last if it were nearby, they follow calculable rules. If the tired light hypothesis were true, the duration of supernova events would be the same regardless of distance, where with the Big Bang theory, far away ones should appear to take longer, in proportion to the distance from the earth. The time dilation matches the prediction of the Big Bang, so we must discard the tired light hypothesis.
Conclusion
The above is just a summary of a much larger body of evidence supporting the Big Bang Theory. With so much evidence behind it, the Big Bang is a robust theory, subject to minor modifications but fully tested on its major premises. We may accept it as a scientific “fact.” More details on the Big Bang are available in some of the works in the section of the Book of Books covering the Big Bang and Evolution. Also, more information on the Big Bang can be found at EvoWiki (www.evowiki.org), and detailed refutations of creationist claims of the origins of the universe are available on the Talk.Origins (www.talkorigins.org/indexcc/) website. If you are interested, please consult those sources for further information.
