more on the expansion of the universe…

Hubble only observed around 46 galaxies. His experiment has been redone with more advanced telescopes, including the space-based hubble telescope.

Again you (qwaider) have hit upon a good point in saying that the data may be deceptive… in science we can never declare a theory ‘proven’ we can only declare it to have ‘strong supporting evidence’, and the more tests there exist for a theory the stronger the evidence becomes.

The expansion of the universe is not only based on the observation of galaxies and their redshift. A consequence of universal expansion is the Big Bang, a consequence of  that is that the universe must be filled with radiation with an average temperature of 2.7K. A measurement of that is in fact is an indirect measure that the conclusion of an expanding universe is probably correct.

Now, the radiation was detected in 1965, and it was found to be homogeneous and isotropic across the sky. This means that no matter where u pointed ur telescope in the sky u would measure 2.7K. This would not be possible unless the origins of the universe were homogeneous across the sky, and also the universe today. This means, observing galaxies in one region of the sky would produce practically the same results as observing galaxies in another region (pretty neat I think).

Again, a precise measurement of this radiation has been made by space based missions (which can detect varations on the micro-kelvin limit) confirm that the average temperature of the radiation regardless of where in the sky is uniform. Check NASA’s WMAP site for more details on this type of mission.

The WMAP sattellite though also measures the light detected by galaxies, so again a confirmation of results done by Hubble type survey’s.

In conclusion, the expanding universe has VERY strong supporting evidence 🙂

hope I have convinced readers… I will get onto the questions on the Big Bang later.

13 Responses

  1. May I throw another stone in the well?
    Historically, we have learned, and relearned, and relearned truth and former “givens”. One was that the earth is flat, ask any scientist few hundred years back, he would convince you that it’s flat. What if, just what if, as we discovered that the earth is really not flat everyone was wrong? And that the expanding universe may well be something that we’re observing from 10 billion years ago, and at the current moment at the edge of the universe it’s collapsing back on it’s self?
    With the expanding universe, comes the ever expanding, accelerating (which I think was proven wrong recently, but only mathematically) and decelerating expanding on the future hope that it will eventually shrink back on it’s own IF it has enough mass, which is still to be determined due to dark matter…etc ..etc

    Yet again, you can’t imagine my joy of hearing this first hand from a cosmologist, its 3 AM here, and I just couldn’t sleep hoping to see the next thing from you, and again, you rewarded me with a fascinating post. I can’t be more grateful, and really excited! I think I’m going to be an official addict to your blog

  2. Quick reply, cuz i need to be up earliesh.

    I am rubbish at remembering greek philosophers names, but I think either archimedes, actually noted that when observing ships coming into harbor from a distance, that he observed the top of their sails first. He noted that this indicated a curved (as opposed to flat) earth, but, he argued that since a god like power would be needed to keep things from falling off a curved earth, and since he was an aetheist, he argued that since god does not exist, then the earth is flat. (I am pretty sure of this)

    Back to the issue though, there is always a margin of error in any theory and it’s observational consequences.

    A universe which is going to close in on it would have a non-flat geometry and more than a certain amount of matter in it. Observation of the radiation (which has traversed the longest distance) indicate a flat universe with critical mass, and a slight acceleration (I am interested to know where the acceleration of the unisverse was disproved mathematically).

    Now, we come to the theory of special relativity, which says that nothing propogates faster than light. So if the primordial radiation is telling us that the universe is flat and ever expanding then we need not worry… since whatever may be beyond the primordial radiation limit of travel, will not affect us. But this needs some discussion of SR, which I will leave for now.

    So yes, we might be wrong, but historically we have never had such precise measurements of astronomical entities.

    p.s. the topology of the universe may be non-trivial, as I read briefly in one of the leading physicists papers, but I did not read it in detail.

    I am actually really pleased to have such interest in what is bascially one of my passions 🙂 I just hope my answers are satisfactory. Have you read Stephen Hawkins: A brief history of time?

  3. Yes, it’s suggested that he stole his work from my 3rd grade science paper 🙂
    I absolutely agree on the non-triviality of the universe topology. And frankly, I doubt that we ever need to worry about a collapsing universe if it will take 13.6 billion years to happen. Since our Sun will have been gone for at least 10 billion years by then. So if we still existed, we probably can traverse to some other universe or somehow counteract the effects
    That mathematical proof was a something that I read couple of months ago, I’m not sure where. I read way too many things to remember (very sorry).
    As for special relativity, I thought tachyons defied it (if they’re ever proved to exist of course) But, there are many that challenge special relativity since it, **fails** to explain some of quantum mechanics phenomena but I love it’s elegance nevertheless.
    Go to sleep …. 🙂

  4. “Now, the radiation was detected in 1965, and it was found to be homogeneous and isotropic across the sky. This means that no matter where u pointed ur telescope in the sky u would measure 2.7K. This would not be possible unless the origins of the universe were homogeneous across the sky, and also the universe today.” – This statement rings a bell for me. In an old blog entry at my blog, I posted a question that has not yet been answered.

    In that entry I argue that since the origins of the world are believed to be a singular point, then the universe should exhibit high symmetry. Since u’re a physicist maybe you can check my entry and give a professional opinion because I have been yearning for one. The entry I am talking about is found here.

    As an additional note, I agree with both of you about the inherent error introduced by observation based science. It is the basis of the philosophical view of scientific fallibilism. Since, I myself support philosophical Skepticism, and consequently admit the scientific fallibilism. I once written an entry called: “Is science justified?” (link), where I argue that scientific fallibilism or Skepticism in general, doesnt mean that science would be completely discredited.

  5. Qwaider: tachyons do not defy special relativity. Basically SR says that one cannot cross the light barrier… from either side. So u start of slower than light, u will remain so, and if u start off faster than light, again u will remain so.

    Also, I think u may be referring to general relativity (inclusive of special relativity). and there is no quantum theory of gravity as yet, models are being worked on, but nothing definate as yet… is this what you mean?

  6. Devil’s Mind:

    Actually, the Big Bang (BB) theory as it stood pre-1980s did not explain the homogeneity of the universe. Simply that, by reversing the expansion of the universe, one finds that with usual expansion, the various regions in the sky never interact. Therefore, one would expect non-symmetry and non-homegeneity.

    A new theory, complementary to the BB, was introduced in the 80s, known as inflation. In which the universe underwent a period of rapid expansion, flattening and homegenising it, prior to the classic BB taking place. The expansion then slowed to what we know it today.

    Thus, there is no singular point where the BB took place… there is no unique point in the universe. The BB happened everywhere.

    Hope that helps 🙂

    p.s. thanks for visiting, i did check ur entry in ur blog and have based my answer on that.

  7. It is a rare occasion to find have a cosmologist answer direct questions about the big bang and stuff. I am glad that I had this opportunity, so please bear with me until I get this thing straight in my head.

    So u’r saying that, the singularity as described in most (school-book) texts (also this image from wikipedia) is NOT entirely accurate description of what is believed to be the big bang?!

    Could you elaborate a little on what it means to say: “The BB happened everywhere.”

    My last question is, if we suppose that a singularity did exist, would my conclusion about the symmetry of the universe hold?! Am I justified to argue that a singularity would conclude symmetry?! I need an expert opinion on that 🙂

  8. Well, I suppose the diagram is a bit misleading. In that the singularity is not a unique point in space-time. One way to descrive this is that we assume the universe started very very small, small enough that each part of the universe could interact together. Then the universe ‘inflated’ i.e. expanded very rapidly, causing the universe to be flat, and homogeneous, also blowing it up to a certain size, then the expansion slows down. You end up with a smooth universe of large scales, there are small variations but these variations are similar everywhere… and they form the seeds of galaxies (much later on). Anyway, here, depending on the mechanism which ‘inflated’ the universe, the substance may decay, (still a topic of research), anyway the traditional big band occurs. i.e. the transition from sub-planckian scales to matter, radiation then onto galaxies and such, and this happens ‘everywhere’ no just in one place.

    What u say about the expansion of a point… in a vacuum, it would imply symmetry. which is one of the reasons inflation works (simply put).

    Nasa has a mini-overview of this here: and

  9. few things,
    Everywhere (must be accompanied by “in the known universe”)
    We have no idea what’s outside this bubble of universe
    We have no idea what happened before big bang
    we have no idea why BB happened to start with
    Inflation may or may not be uniform over the flat space. If there was anything else, we would have no ideas
    sub plankan dimensions [may] still exist (what if a Big-Bang happened in the middle of a big-bang?)

    God I love these subjects … please continue … please

    Your blog should be called: PaliCosmologist! What do you think?

  10. lol, seems I have dug myself a nice little ditch here 😀

    1- everywhere is usually referring to our local universe, yes.

    2- no, we dont know what happened before BB

    3- if by BB u mean the traditional nucleosynthesis part, then inflation provides a framework for which it will happen. If u are starting with inflation, some models give a consistent series of events from inflation till BB, others require the introduction of other mechanisms. Inflation is driven by the most simplest particle physics entity (scalat field)… in other words, uncertainties in the vacum state of the universe (quantum mechanics). There are more exotic theories involving extra dimensions and such. One can argue that the universe was in vacuum, QM dictates that the quantum fluctations could have any value, or that each part of the universe had a different value, one was bound to be the one necessary for the subsequent evilution of the universe.

    4- whether the universe was flat or not, inflation guarntees the eventual flatness of the local universe, pushing all the bit we dont want out into the vastness of innaccessible space (in a manner of speaking). Non-uniformities in the expansion would manifest themselves in the observable radiation, and so far should deviations from this exist, they will be subdominant to the unifrom ‘bits’, but may still exist (next step in research).

    5-subplankian dimensions may exist… but subplankian scales must exist.

    6- BB occuring in BB? u mean inflation occuring within BB? i would imagine this would result in the dilution of large scale structure, universe less populated than it is now… possible disintegration of things that had formed (inflation goes on too long). I am just guessing here… there is some evidence for the accelaration of expansion, i.e. new age inflation 🙂

    7- i thiknk i will keep my blog name 🙂 but thanks 🙂

  11. I LOVE how you put things … absolutely enjoy every second of reading …
    Thank you .. thank you sooooooooooo much

    Now, explain to your humble fan, what does “Loolt” means, and if you have a different choice, what would you pick?

  12. I am glad it is coherent and that you have enjoyed it 🙂 It has been my pleasure 🙂

    Loolt is just my nickname at home 🙂

  13. Hi,
    I found your blog via google by accident and have to admit that youve a really interesting blog 🙂
    Just saved your feed in my reader, have a nice day 🙂

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