The illusive Space-Time: How large is the Universe?


Spacetime fabric

Spacetime fabric (Image Courtesy Wikipedia)

No matter how hard I think, I can’t even come close to visualizing space time. And I am sure not even Einstein could , though he was the one who came up with the counter-intuitive and bold concept of time dilation. While the maths is absolutely spot-on and it has lived up almost a century now, describing the world at an macro scale scale (yes, the quantum world has got a different set of maths), I am sure it would take us ages to be able to engulf it (but if Darwin was correct, we would ultimately “evolve” to be able to visualize it, provided we survive long enough).

Anyways, to cut it down, I somewhere read that the diameter of the observable universe is about 97 billion light years, i.e. it is about 48.5 billion light years radially.  How can that be? If nothing can travel faster than light, and the age of the universe is about 13.7 billion years (that is when the big bang happened) how could there be anything visible beyond 13.7 billion light years? This question (and a 100s of others) pop-up every now and then to me. I am lazy enough to sit on them for quite some time until it starts disturbing me. And this one did! And it took just about 10 minutes to get the answer (or rather explanation). So the idea is that the space itself can expand. I knew space could bend, but now I know it can expand as well. Well, even if the space expanded at the speed of light, the radius of the universe should have been about 27.4 billion light years. But that is not the case. The answer to this is that space did not respect Albert Einstein and it decided to expand faster than the speed of light! Wow, isn’t that really cool? With this, even if someone says that the universe is a billion billion quadrillion light years in the diameter, you can’t question that, could you? I noticed that there is already the notion of *observable* universe. There are things beyond that, which we can’t see.

Could the mysterious and illusive dark matter, which is yet to be understood throw some light on it? To me space itself  is nothingness (though it can be filled with something), and how could nothingness expand? What if the dark matter (or something else) is such that it makes light travel ridiculously slow when it passes through it? Wouldn’t it make all our distance observations overestimated? Well I know, there are enough reasons for this not being true, else someone would have brought it up for sure. But the point is that it looks to me,  that in the last century or so we have created a complicated  aura around all this. It has to be simpler. It really has to be. Otherwise it is not true.

Cosmology has always attracted and eluded me since childhood. I just wish that during my lifetime, we witness a spectacular theory or discovery which takes us a step ahead. Wouldn’t it be cool if we discover the mysterious dark matter? Or the fact that things can travel faster than light? Or something more beautiful than E=Mc2

And then, there’s quantum mechanics. I wouldn’t talk about it in this post at all. Einstein wouldn’t have liked it 🙂


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Amit Srivastava

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Ankit - May 1, 2011

Actually, I’ve been doing a bit of reading on this topic lately. Cosmology is fascinating, and screws with your mind. Some common pitfalls:

* the 97 billion light years number is just the diameter of the *observable* universe, due to light speed limitations. There may be more out there that we may *never* know anything about.
* There is no ‘edge’ at the end of the universe, the most popular interpretation today seems to be that the universe is in fact infinite in extent.
* Photons, since they travel at the speed of light, do not feel time. For them, the big bang is the same instant of time as right now!
* The universe, in fact, *does not* have Eucledian geometry. Remember the axiom we all learned, that two parallel lines will never intersect? Well, that’s not true for the *observed* physical universe. Mass bends space & time. Eucledian geometry is just an approximation of the world, when you’re using small enough scales. For more, read up on something called “Minkowski space”.

PS: I just culled this list from regular reading of http://www.reddit.com/r/askscience/, and my understanding is probably flawed in nature. For an example of the types of gems that are present in that subreddit, read: http://www.reddit.com/r/askscience/comments/fjwkh/why_exactly_can_nothing_go_faster_than_the_speed/c1gh4x7

Srivatsan - May 1, 2011

Amit, a friend of mine is conducting this workshop http://fadereu.posterous.com/knk102-online-workshop-may15-july-30-2011-the which I think you might find madly interesting.

You should check it out.

Amit Srivastava - May 1, 2011

@Ankit: Thanks for the pointers. Good that you’ve been reading up on this as well. Let’s catch up on this when we next meet 🙂

@Srivatsan: Interesting link. I will try to attend this!

Amit Srivastava - May 3, 2011

There are some good documentaries here as well:


I liked the “Through the Wormhole” series.

So much information lying around, so little time :-). I wish I could get back to studies and take up cosmology for a couple of years!!

Ankit - May 4, 2011

I like videos, but end up just downloading & saving them for a hypothetical ‘later’ date that never does arrive.

Amit Srivastava - May 5, 2011

I used to do the same until the Riyadh trips happened! I’ve stopped downloading and watch them online as and when I get time. There’s so much to do and so little time!


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