Physical Cosmology

By Michael on October 10, 2007 at 2:35 pm | In Blog Posts, cosmology |

I am taking a cosmology course, which explains my recent (and probably upcoming) posts on cosmology. One thing people ask often is whether cosmology is metaphysics or philosophy more so than a science. It is hard for people to comprehend that we can test our theories in cosmology even though we can’t rerun the experiment.

Nothing could be further from the truth. Cosmology is a physical science and it is a rigorous science. While there are certainly mysteries and unknowns, cosmology is on a very firm basis and really doesn’t resemble philosophy in the slightest.

If you are interested, our textbook is very readable and was recommended to me previously by another cosmology researcher. It’s Introduction to Cosmology by Barbara Ryden. Dr. Ryden does a very nice job of laying out the context in the early chapters and then delving into the details of physical cosmology in the later parts of the book.

Today in class we talked about the evolution of the universe in 3 main eras — the radiation dominated early universe, the long matter dominated universe, when galaxies formed and the present era where the universe is dominated by “dark energy” (known to cosmologists as Λ). The radiation dominated era was quite brief, lasting only about 50,000 years. The matter dominated era was about 9 billion years long and Λ has dominated for about the last 4 or 5 billion years or so.

We know this.

3 Comments »

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  1. The portion of cosmology that falls into metaphysics is the speculation on what happened prior to the Big Bang, the existence of other universes, etc, for which we will never be able to obtain any evidence.

    This metaphysical speculation is often an attempt to explain the fine tuning of the universe by people who refuse to see the hand of a designer in the cosmic creation event that we call the Big Bang.

    If you haven’t read “The Creator and the Cosmos” by Hugh Ross; I highly recommend it, or check out Hugh’s website: http://www.reasons.org.

    Comment by bmartinf — October 15, 2007 #

  2. You bring up one physics issue and one religious one. The physics issue may or may not be true i.e. we may be able to figure out things prior to the Big Bang. Maybe not, but maybe. Just like we didn’t used to think we’d ever understand stars and now we understand them very well. I agree that there is a lot of speculation that is probably not science concerning causes of the Big Bang.

    But in regards to your religious point, “the hand of the designer” is in the eye of the beholder. We don’t know why the Big Bang banged but claiming it was a designer doesn’t gain us anything. Maybe it’s true, maybe it’s not, that is truly speculation. The anthropomorphic principle refutes a lot of those issues about how we wouldn’t be here if things weren’t exactly just right.

    Comment by michael — October 16, 2007 #

  3. I was not intending that we should stop studying the natural world around us and instead resort to “…and then a miracle occurs”. To the contrary, the significant gains in understanding over the last century have restricted the number of possibilities for origins of the universe and have shown us how special we are. Prior to Hubble’s research, many people thought that the universe had been in existence since infinity past. Because Einstein believed in a static universe, he added his cosmological constant initially to counteract the expansion of the universe that we now accept as evidence of the Big Bang and hence a beginning of the universe. This forces the discussion about what caused the Big Bang. As we continue learning about dark energy and dark matter, we will be able to further refine our models of the beginning of the universe.

    The Anthropic Principle (http://en.wikipedia.org/wiki/Anthropic_principle) does point to our current place (in space and time) in the universe being special, but to me it also highlights that there are certain parameters that require fine tuning for us to be here.

    Comment by bmartinf — October 23, 2007 #

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