Wednesday, February 17, 2010

Reflections on the Size of the Universe

I believe the Hubble deep field images are among the most awe inspiring photographs ever taken and I have recently set the Ultra Deep Field up as my desktop background. To take this image the Hubble telescope was pointed at an area of space devoid of  nearby stars and an image of deep space was constructed by accumulating data over a period of several months. The total area encompassed is equivalent to a speck about one millimetre squared held at arms length. Yet this tiny tiny window on the universe is crammed full of galaxies. Each of these galaxies likely has billions of stars. This image contains some of the farthest away objects ever observed - galaxies at a remove of billions of light years from our own.

This number of worlds, these distances, these time-scales are completely mind boggling. They are in truth simply unimaginable and yet they exist. Here is the picture:

 
(Image in the public domain courtesy of NASA. A high resolution version can be got from Wikipedia )

One thought that immediately strikes me as I contemplate this picture is how inconceivable it is that our humble sun is the only place in all of this immensity where the miracle of life came about. The universe must teem with life, just as it teems with stars. Why then have we not heard from any one else?  Science fiction writers have proposed many reasons ranging from the benign (our development is being quietly observed from afar until such time as we are judged fit to join the congregation of space faring races) to downright scary (some malevolent force  systematically eliminates all space-faring races).  Could it be that life evolved elsewhere is so fundamentally different as to be unrecognisable to us or is it  simply due to the immense distances involved and the tyranny of the un-attainable speed of light?

The second thought that strikes me is how this immensity exposes the arrogance of that branch of human science known as cosmology. Hypotheses such as the big bang, black holes and dark matter are afforded the same respect as established scientific fact when they are really no more than extrapolations built upon extrapolations. Extrapolation is a useful tool that allows us to use those things we know to make predictions about those things which are outside of our current scope of knowledge. However every extrapolation incurs uncertainty and the further we go from the dataset of the known the greater the uncertainty.  Thus knowledge gleaned on Earth of how things move and interact had a reasonable chance of holding up when extrapolated  to the neighbouring planet of Mars and indeed the experience of the Mars landers has shown that the extrapolation was valid. Cosmologists extend such extrapolations a billion billion times further though and the uncertainty becomes so large as to render the extrapolations completely useless. 

There is nothing new about this - every era has had its cosmologists who confidently claim to have the full and true explanation of the universe. Just as today the proposers of such theories have often been held up as mystical geniuses safe in the knowledge that no one was likely to be able to prove them wrong. This is not science. It is closer to religion than science and indeed it was real evidence based science that eventually exposed the cosmic eggs, the celestial spheres and the epicycles for the failed extrapolations that they were. I will therefore make a bold extrapolation of my own: I believe that in years to come the cherished cosmological hypotheses of today will similarly perish beneath the ongoing march of real evidence based science and children of a future age will look back and chuckle at our big bangs and black holes with much the same amusement that we feel when considering Ptolemy's epicycles.

14 comments:

Cap'n John said...

Many many years ago when Earth was the center of the universe and the sun, moon & stars all revolved around it, the world was actually flat, and any ships who sailed too close to the edge fell off and were never seen again.

This was a well known and accepted belief held by many people of the day, including respected & learned teachers & leaders of society, and anyone who dared speculate anything different (such as the earth actually being spherical and orbiting around the sun) was laughed out of town...if they were lucky.

Technology advanced, and now we know better.

Currently many people believe we're alone in the universe. That we're it, there is nobody else.

The cool thing about people who believe this is they cannot prove they're right, and so they cannot prove we're wrong. This makes their belief an excellent hypothesis because it can only be disproved.

Back then, people not only believed the world was flat but it was accepted as fact.

Now, some people believe we're alone in the universe. Like yesteryear's flat landers, their belief is sustained only through the limitations of current technology.

Tipa said...

True science never claims to have firm answers, just theories that best explain what they observe. Cosmologists would be among the last person to insist they know the underlying mechanism of the universe.

Due to the background radiation of the universe, the S/N ratio of our most powerful transmissions drop below usefulness after (IIRC) a little more than one light-year from Earth. Given our brief history as a technological species, the chance that we would receive signals from another civilization at our similar level of progress from close enough to rise above the background noise is zero. Given that interstellar travel is almost certainly impossible, it's no wonder why many people would find it easy to believe we are alone in the cosmos.

And we have no basis to determine how common life is in the universe until we find it someplace else... as much as we want to believe life evolved elsewhere, we can't know it as a fact until we see that it has happened.

If we find that life evolved first on Mars, and then the catalyst for life on Earth was carried here by a meteorite torn from Mars, then aside from finding out we're all at some level Martian, nothing has changed.

mbp said...

Yup Capn' John the limitation of our current technology technology prevents us from discovering if there really is life on other worlds. Unfortunately though as Tipa points out we may never have the technology to find out.

As Tipa says: "interstellar travel is almost certainly impossible"

I find this one of the most profoundly depressing results ever to emerge from science. The truth is we may never travel to other stars. The enormous distances of interstellar space may condemn Mankind to be trapped forever in this one solar system with its one inhabitable planet.

Deep deep down I want to disbelieve this. I hope against hope that this is not the case that it is only "the limitations of current technology" and that new discoveries will show us the way. But ... and this is the awful awful but: If Interstellar travel is possible, why haven't we seen some interstellar travellers from more advanced worlds already?

Cap'n John said...

Galileo was persecuted for his beliefs, but just 200 years later it was a well established fact that the earth was not flat, while people like Sir George Cayley were respected for their work on heavier-than-air flight. In 1903 the Wright brothers made their first powered human flight, the 1930s saw the introduction of the jet powered aircraft, and just 40 years later Neil Armstrong walked on the Moon.

And you dare to propose that interstellar travel is almost certainly impossible?

Ha! I say to you. Ha! (Of course I mean that with the utmost respect ;)

I would put forth that by July 20, 2069, interstellar travel will not only be possible but a reality.

Either that, or we'll have blown ourselves up and be living like Mad Max :P

Anonymous said...

One way trips of long distance coasting will be possible based on current theories. And regular fire-and-forget directed communications to give updates on progress.

But, obviously, this approach will be very slow, costly and only committed to as necessary rather than as a rush to fill space. And such activities certainly won't be visible to others watching.

The Big Bang theory is quite reasonable, the CMB is proof of something to that effect having occurred. The details are guessed somewhat but it does fit. Cosmologists aren't just saying it was that way with no observational reason for it.

A good way to think about such questions is what is the politics for such a story? Who is pushing the idea? When a head of government decrees it as so with no science to back it up you've got a good case to argue for it being bullshit.


Solbright

Anonymous said...

And given the amount of bullshit I've heard in recent years I'd also like to point out that science is not political in nature.


Solbright

mbp said...

Hi Solbright I don't deny that the theories in vogue today fit the known facts. It is just that the known facts are such a tiny subset of what we would need to know that I think it is almost inevitable that current theories are not just wrong but probably completely wrong. It is like the Hindu parable of the blind men and the elephant only on a much larger scale. Imagine if each blind man only saw one atom taken from a random part of the elephants body.

With regards to interstellar travel - I really really hope that we discover something that makes this feasible within human timescales - but I do keep coming back to the question of why we haven't seen others do it. Perhaps life as we know it very rare and sparsely distributed. I don't know.

Anonymous said...

Well, I feel you've very much got the wrong end of this stick. I suggest doing some reading before comparing science to a religion.

While popular theories may be wrong at times the scientific method eventually works out the kinks.

Religion has functions but explaining reality is not one of them. When a religion gets used in this manner it's to explicitly not explain, as in "God made it that way" with an implicit don't ask questions.

Science and religion shouldn't be in conflict. But, sadly, religions are too easy to politically abuse.


Solbright

mbp said...

Solbright I am not comparing science in general to religion. I am saying that some disciplines which purport to be science (in particular cosmology) are not all that scientific.

The scientific method is a systematic EVIDENCE BASED method of acquiring new knowledge that has a solid record of success. Cosmology on the other hand has a habit of getting way beyond the "evidence base" and drawing conclusions which are wild extrapolations. This is not a new thing. It has always been thus.

Anonymous said...

We do have rather good evidence for the Big Bang (Or an equivalent). Eg: There is an oldest light reaching us. If the universe was older we'd be able to see further back in time. And, as I mentioned before, the Cosmic Microwave Background radiation fits this theory too.

I'm sure there are other observed facts also, but like you, I don't try to dig deep.

Anonymous said...

One part of the Universe that is a complete unknown so far is it's size. The huge distances we can already see doesn't in any way define a limit on the farthest star. It only says we can't see any further than the oldest light.

I'll now speculate on that point: Combine that with a possible instant gravity (Gravity waves still haven't been observed) and you have the makings of dark energy, not to mention the interstellar travel so desired.

You are correct about these "dark" things being very speculative. But then they are only a filler label for what is not predicted by accepted theory. And that's how scientists treat them. As something still to be figured out. Something to be included in a more complete theory.


Solbright

Tesh said...

Thankfully, honest scientists make no such claim to Absolute Truth. Cosmologists do indeed tend to work "way out there", but then, that's sort of the nature of the beast, as with theoretical physics and such. So long as they accept corrections when we manage to find them, there's nothing wrong, and indeed, that sort of "intellectual frontier" is a big part of what makes cosmology interesting. :)

Oh, and have you seen the pictures over at the Gigagalaxy Zoom site? I had the Milky Way picture from there as my desktop for a long time.

http://www.gigagalaxyzoom.org/about.html

mbp said...

That gigagalsxy is a terrific website Tesh, thank you for the link. There are so many wonders to observe and all of those pictures are taken from our own galaxy. Of course just when I am completely overwhelmed by the immensity of the Milky Way my eye turns back to the hubble deep field and I realise that each of those dots in that picture is an entire galaxy in its own right and my head completely explodes. It is absolutely mind boggling.

Thallian said...

I personally belief that interstellar travel is not only possible, but routine for spiritual beings, but that's just my beliefs. As far as our lowly technology being able to do it, prolly not for a long long time. (Even at our current phenomenal rate of technological advancement, it'll take quite a while.) I personally believe Einstein's theory was wrong and matter CAN travel faster than light speed, but getting it there prolly requires things we don't understand. Great article and thoughts/comments btw.