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How accurate is this short summary of physics history?

  1. Jun 20, 2011 #1
    For personal purposes, I'm trying to summarize the last 14 billion years. How accurate is the following? Any thoughts welcome, thanks!

    Most scientists believe the universe is at least 14 billion years old based on evidence about the relative movement and expansion of galaxies and other information. And further, that at that time, all the energy in the universe was concentrated in one point which exploded in a very hot Big Bang. There is no evidence for what, if anything, existed before the Big Bang, or if the initial conditions were somehow created. The theory continues that as the universe expanded from the Big Bang point, it cooled down and gravity pulled together stars into galaxies.

    A star is a massive ball of hydrogen and helium (both created in the Big Bang), the two most basic chemical elements. The star fuses these two elements in a process called nuclear fusion which produces heat, light, and forges other chemical elements. As the star ages, it produces more and more heat and light, until it collapses into either a dwarf or a supernovae, and in the latter case, finally a neutron star or black hole. A supernovae expels most of its contents during an explosion. It is also so hot, that it is the source of the rest of the chemical elements, and may be the source of more complex things such as the origins or building blocks of life itself – molecules.

    The Earth, or The World, is the third closest of eight planets to The Sun, which together make up our solar system (which is part of the Milky Way Galaxy of solar systems). The planets orbit around the sun due to its gravity. The planets were created from molecular clouds after star formation, and coalesced due to gravity. The Earth is about 4.5 billion years old.

    I can't philosophically describe how life is different than an inanimate object like a rock, but many scientists consider life to be a form of chemistry leading to a self-sustaining growth and reproduction process. It is believed that life on Earth started as a self-replicating molecule about 4 billion years ago. Further, about 3.5 billion years ago, DNA was formed which was an instruction set for building the proteins of a self-replicating organism. About 3 billion years ago, photosynthesis, the production of energy from light, started, with oxygen as a by-product.

    A cell is the basic unit of life and encapsulates the DNA, energy production, and other things. It is believed that multi-cellular life (cells that can reproduces themselves using DNA) began on Earth about 600 million years ago. The theory of evolution states that multi-cellular life evolved into different species of organisms based on mutations and natural selection. The cambrian explosion occurred about 570 million years ago and included many new animals, particularly under water. About 475 million years ago plants appeared on land. About 200 million years ago, mammals (warm-blooded vertebrae with hair, milking females, and birthing live young) appeared on land.

    About 65 million years ago, primates appeared (e.g. monkeys). About 2.5 million years ago, the precursor primate to humans appeared. About 200,000 years ago, homosapiens (humans) appeared, living as hunters and gatherers (a distinct but related animal, neanderthal appeared at about the same time, but was extinct by about 30,000 years ago). About 10,000 years ago, trade, agriculture, language, and technology bloomed human societies.
  2. jcsd
  3. Jun 20, 2011 #2
    Just a few thing I noticed:

    You jumped from Big-Bang to stars and galaxies. There is a big missing piece here, mainly how you get from the Big-Bang to stars (Big-Bang to matter to stars to galaxies?)

    “produces more and more heat” and “until it collapses” doesn’t really follow logically. You might want to fill in some more information (until it runs out of fuel and collapses due to its gravity?). Also “collapses into supernovae”? I know they are related but a collapse is quite opposite of a huge explosion (supernovae). Might want to expand slightly on this (collapses so violently that it rebounds into a great explosion, a supernovae?....although I’m not sure if that’s actually what happens :) )

    Also, you say the star forges “other chemical elements” and a supernovae is the “source of the rest of the chemical elements”. You might want to specify which elements a star forges (light elements or light elements up until iron) and which ones a supernovae (heavy elements or elements heavier than iron).

    Is this true? I don’t know, but it sounds like speculation.

    Sounds like your definition of multi-cellular life is wrong here, or way too general. (Single-cellular life also reproduces using DNA).

    Besides that I see nothing fundamentally wrong with it.
  4. Jun 20, 2011 #3


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    A more accurate description would be that the universe cooled down and formed massive amounts of Hydrogen and Helium which was then pulled together by gravity to form galaxies. The gas continued to collapse within galaxies to form stars.

    I think the last sentence is unnecessary. Also, my personal opinion would be to change the description of the stars aging to something like this: "As a star ages, it begines to run out of fuel. Small stars swell into Red Giants before running out of fuel and collapsing to small hot balls of non-fusing gas called a White Dwarf. Larger stars can fuse elements other than Hydrogen and Helium together, with the most massive ones producing elements up to Iron before they run out of fuel and explode into supernovas, leaving behind a very dense core called a Neutron Star or collapsing into a Black hole."

    While pretty much correct, I don't really like the layout here. I'd say something along the lines of: "The solar system was formed by a collapsing cloud of gas about 4.5 billion years ago. Most of the gas formed the sun with the remaining small percent forming the planets." Then add the rest as you see fit.

    This looks pretty good to me. I'd just double check your numbers just in case.

    The rest of it looks alright. I'd be sure to focus on the presentation of it. The actual layout of the sentences and such to make it look and read a little better.
  5. Jun 22, 2011 #4
    Thanks for both replies!
  6. Jun 22, 2011 #5
  7. Jun 22, 2011 #6
    You mention that the universe was created by the Big Bang which was a point source of energy, but cosmologists are not entirely sure this is true. Today, the universe appears to be perfectly flat, meaning it is infinite and was always infinite--implying the big bang was an "explosion" of a point source of infinite energy density at every point in the universe, which was diluted by the expansion of the universe.

    Also, if you believe Inflation theory: the universe was more likely either closed or open during the big bang, and a early period of rapid inflation caused the universe to be approximately flat. Here there are two theories as to the nature of the big bang. If the universe was open to begin with, it would be described by hyperbolic geometry and would be infinite, even at the Big Bang. If it were closed to begin with, it would be described by spherical geometry, and would be a finite size. This latter case would result in a point source Big Bang, so it's very possible, but we have no way of being able to tell unless we could retrieve information about the density of the universe before about 10-36s after the BB.
  8. Jun 22, 2011 #7


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    This is all you need to know:

    Our whole universe was in a hot dense state,
    Then nearly fourteen billion years ago expansion started. Wait...
    The Earth began to cool,
    The autotrophs began to drool,
    Neanderthals developed tools,
    We built a wall (we built the pyramids),
    Math, science, history, unraveling the mysteries,
    That all started with the big bang!
  9. Jun 22, 2011 #8


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    The BB was not an "explosion".
  10. Jun 22, 2011 #9
    Hence the quotation marks.
  11. Jun 22, 2011 #10


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    Saying something is something when it is not - is not ameliorated by putting quotes around the thing it is not.

    Like if I said Bob is an "idiot". :devil:

    The Big Bang was neither an explosion nor an "explosion"; that is a highly misleading claim.
    I know. I made the same mistake here (when I was young a foolish) and got sternly corrected.
    Last edited by a moderator: Jun 24, 2011
  12. Jun 22, 2011 #11


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    Back in his day it was the Small Pop!
  13. Jun 22, 2011 #12


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    Back in my day it was breaking news... :biggrin:
  14. Jun 22, 2011 #13


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    Yes to this! :biggrin:
  15. Jun 24, 2011 #14

    Claude Bile

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    I would say that the second paragraph is somewhat superfluous, it switches from the past in paragraph 1, to the present in paragraph 2, then to the past again in paragraph 3.

    Other than that, it is a fairly reasonable summary, depending on exactly what message you wish to send of course.


    P.S. DaveC, gold.
  16. Jun 24, 2011 #15
    I hope you had to google that or have you learnt it off by heart?
  17. Jun 24, 2011 #16


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    We recite every day. (My wife always muddles up the final BANG! though. There's two. She puts the emphasis on the wrong one.) :biggrin:
  18. Jun 24, 2011 #17
    So it's ok to call it the "Big Bang", but not ok to say "explosion"?? :P

    You're right, explosion is not an accurate description for the Big Bang, and I understand why, (my Cosmo professor this year had to drill that into our heads a few times), it's just a convenient simplification for "infinitely hot and dense state that expanded and cooled with the universe." In the future, I'll be sure to state it more aptly, lest my slip-up again not go unnoticed by a smarter physicist than I ;)
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