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My question is related to the base of cosmology science and theories.

If all what we know about cosmology science is based on our observation from sky and whatever we observe goes back to thousand and million and billion years ago, how can we be sure about some theories like universe expansion. Maybe universe is back to contraction as we talking now?

  • Jan 6 2014: Science is not about certainty. Being "sure" is for religions.
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    Jan 7 2014: All the stuff, I have recently read says that galaxies are moving away from us. Some pretty good math backs that up. So away would indicate expansion... seems simple enough.
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    Jan 7 2014: Oh we cannot be sure, but just to say that the universe is contracting without placing evidences (testable) will not be a theory - it will be called a conjecture.
  • Jan 6 2014: I think the thing to keep in mind and be open minded about is that as our tools develop, we get a deeper and clearer view of the nature of the universe and the nature of reality. The very fact that we don't have a T.O.E. that can incorporate relativity and quantum mechanics means we don't yet have all the answers.
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    Jan 6 2014: Jimmy, I believe that there are many as yet unknown or unperceived things which may be currently present, and also that there may still be new ways of interpreting things that we know exist and which we believe in.

    I'm certainly not saying that I have any insights into what these new things or any novel interpretations about them; in fact, I would be hard-pressed to even suggest what they might be.

    My main thought, and what thrills me the most about the unknown, or the untested, the unproved, is that there's more knowledge and new worlds yet ahead.

    As Shakespeare's Hamlet suggests:

    " And therefore as a stranger give it welcome.
    There are more things in heaven and earth, Horatio,
    Than are dreamt of in your philosophy."

    Hamlet Act 1, scene 5, 159–167
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    Jan 5 2014: Fortunately, there may be far more to learn than what we have learnt so far, or at least deduced, inferred or concluded. Much of what is yet to unfold may seriously undermine our past and present thinking, but one thing is likely: some day our party may be over, but the road, most likely, will never end.

    The Road Goes On Forever and the Party Never Ends, by Robert Earl Keen
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      Jan 6 2014: There will always be more to learn, but for me there's no reason to believe in things that I don't have significant evidence to believe in.

      Usually when people say that there's more to learn they think (not saying that you are doing this Don) that they have the answers and that people should listen to them and not the "close-minded sciences". What they often don't understand is that science is always looking to prove itself wrong. If someone would provide proof against the Theory of Relativity or Evolution a Nobel prize and instant fame is theirs.

      We can choose to believe in whatever but it does not make it true, and there's a real danger in thinking that you know better (again not saying you do this Don) then the smartest people in each scientific field, that people criticizing often have a very limited understanding of.
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        Jan 6 2014: "...[We]'ve been with the professors and they've all liked [our] looks
        With great lawyers [we] have discussed lepers and crooks
        [We]'ve been through all of F. Scott Fitzgerald's books
        [We]'re very well read, it's well known
        But something is happening here and you don't know what it is
        do [we], Mr. Jones?..."

        - from Bob Dylan's song, Ballad of a Thin Man'
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    Jan 4 2014: It's very well explained by the Redshift, that is perhaps our biggest proof, but there is an ocean of proof that supports this.


    To understand what the Redshift means you have to understand some about the electromagnetic spectra. And I'm not going to be able to teach physics here on TED conversations.

    If you wish I could provide you with the online sources to learn physics...
  • Jan 4 2014: They're called theories because they aren't fact yet. It's kind of hard to reach the edge of the universe and observe it's expansion. We come up with theories as approximations to facts, and we go from there. Our current tech is mostly built on theories, and so far we got humans to the moon, rovers on mars etc
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      Jan 4 2014: This is perhaps something that I come across very often that still manages to annoy me, people don't know what theories are, and I'm sorry Jean but neither do you.

      "Theory is a system of ideas intended to explain something, such as a single or collection of fact(s), event(s), or phenomen(a)(on). Typically, a theory is developed through the use of contemplative and rational forms of abstract and generalized thinking."

      A fact is just something that we have data that supports it, a theory is the highest rank that a human idea can have, please understand this. A theory makes predictions about the world based on facts and ideas put together. And every one either stands the tests that it's being put through or fails and is dismissed, this is how our understanding of the world continues to grow.

      Some of the best tested (which means that no one has been able to provide facts that contradict them) theories that have stood the test of time are: Evolution, Gravity and Big Bang. They may fall some time in the distant future, but there is no reason to believe so today, unless you just want to think that you are smarter then all the smart personas that have ever lived collectively.
      • Jan 4 2014: You didn't say anything that I didn't say, you just went more in depth with your description. A theory is not a fact, but is close to being one since they do tests and collect data from observations and come with rational deductions. We used to think that the earth was flat (was a theory), until someone proved otherwise. We used to believe that the earth was the center of the galaxy (was a theory) until the heliocentric model proved it wrong.

        That's why they're approximation to facts, close but not yet. It won't take long before most of our beliefs in Physics get shaken by the next genius to cine up with a breakthrough theory. I'm not saying that a theory is false, it is true to a certain extent, but is not a fact. What do you think I meant in my comment?
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          Jan 4 2014: I think that you are confusing the word theory and fact and the actual implications of it. It's a very common mistake.

          You see a fact is simply "The apple falls to the ground" is does not say anything more than that.

          A theory is "The apple falls to the ground because of gravity", which also makes the prediction that other objects of mass will fall to the ground. A theory is useful for understanding the world, a fact without a theory is nothing as it may be interpreted however people wish.

          Like "The apple falls to the ground" because god pushed it or because the apple wants to be close to the ground. It does not give us any predictions of the world that we can hold true.

          To get theories we must combine a myriad of facts and make and draw conclusions from them that can be tested.