Science has been outstandingly successful at investigating and understanding the natural world and, so, it is always surprising to be reminded of the many fundamental questions that science still cannot answer. Today I will briefly look at a few of these questions.
1. What is the nature of dark matter?
Almost 100 years ago astronomers noticed that distant galaxies hold more matter than is accounted for by the visible material. This missing matter, called “dark matter”, accounts for 27 per cent of the mass-energy of the visible universe and played a significant role in determining how the universe evolved.
The popular scientific guess is that it is composed of fast-moving particles that interact so weakly with the ordinary (baryonic) matter of stars and planets they can pass unimpeded through many kilometres of ordinary matter. But, to date no such particles have been detected and the basic nature of dark matter remains a mystery.
2. What is the nature of dark energy?
Prior to the 20th century astronomers believed the universe was static but in 1929 Edwin Hubble discovered the universe is expanding. The Hubble space telescope later (1998) showed, not only an expanding galaxy, but a galaxy expanding at an accelerating rate, propelled by a mysterious force called "dark energy".
This dark energy constitutes a whopping 68 per cent of the mass-energy of the universe, playing a more important role in its evolution than dark matter. The fundamental nature of dark energy remains entirely unknown to science.
3. What happened before the Big Bang?
We know that the universe began in an explosion – Big Bang – at a point 13.8 billion years ago and it has been expanding ever since. Although it is possible that the universe goes through endless cycles of expansion and contraction, the conventional scientific view is that everything began in the Big Bang, including time itself.
So, asking what happened before that is meaningless – there was no “before”. Few scientists are satisfied with this answer. Some think time didn’t begin at that point but only when the universe reached a certain level of complexity. General relativity explains the structure of the universe but the theory breaks down when scientists very closely approach the Big Bang itself.
4. Are we alone in the Universe?
The visible universe contains at least one trillion galaxies and we live in the Milky Way galaxy which contains more than a hundred billion stars. Many stars are orbited by planets and Nasa data suggests that up to 20 per cent of planets are potentially habitable. Our galaxy alone hosts 33 million potentially habitable planets.
It seems highly unlikely that we humans are the only intelligent beings in the universe, given such extravagant profusion of planets. The search for extra-terrestrial intelligence (Seti Institute) scans the sky in search of radio signals broadcast by alien civilisations. So far Seti has detected no intelligent signals but has targeted only a few thousand stars to date. However, it remains early days.
5. The puzzle of the human brain and consciousness
The human brain is the most complex thing in the known universe. It consists of 86 billion nerve cells interconnected to each other through two types of cell extensions called axons and dendrites. The brain makes abstract thinking, language, technology and consciousness possible. Consciousness is the most amazing consequence of the brain.
We are not simply capable robots able to hold information, respond to environmental signals like noises and smells, but “dark” inside. We think; and we know that we think – we have an inner life. How does the 1.4 kg brain produce immaterial thoughts? This is known as the “hard problem of consciousness”. [Tom Stoppard’s play The Hard Problem deals with consciousness – he clarified a possible misinterpretation of the play’s title by explaining: “It’s not about erectile dysfunction.”
Many people think science is well along the road to understanding/explaining the natural world. I think it is much more likely that we have only started along this road.
It is chastening and embarrassing to scientists that, at the moment, we only understand the nature of 5 per cent of the fabric of the universe. But this is a good problem to have.
There is nothing to rival the thrill of unravelling the mysteries of the natural world. Huge mountains remain to be climbed. Possibly the most difficult ascent of all will be to scientifically account for the self-conscious human mind.
- William Reville is an emeritus professor of biochemistry at UCC