Answers to the big questions about how physics shapes our understanding of the world and the universe around us.
Perhaps you've read about ambitious physics projects like the Large Hadron Collider at CERN (the European Organization for Nuclear Research) and wondered 'Why do we need particle accelerators? What will they tell us about the world?'
Our independent expert Professor John Pethica has answered some of your most pressing questions about black holes, space travel, time...
Question 1
Is the human mind quantum based?
Prof Pethica: In the obvious sense that the brain is made up of matter which is governed by quantum processes, and the mind is believed to be associated with the brain (i.e. scientific evidence of mind without brain is rather weak) then yes.
However, it is worth recalling that complex dynamical systems can have randomness and uncertainty (chaos) as a property, without requiring quantum processes. The quantum uncertainty just increases this. Very complex systems, such as the >10 billion neurons in the brain, can have surprising and unexpected properties (often called emergent properties) which are not at all apparent from the properties of the individual components. This is a very interesting and challenging area of science and technology.
Question 2
Is there any proof for String Theory?
Prof Pethica: It is highly unlikely that there will be any experimental support or evidence for string theory any time soon...
Question 3
Is it possible for a human being to travel at the speed of light?
Prof Pethica: Within our current understanding, which is extremely well supported by experimental evidence, no. When we talk about speed we mean distance per unit time. At high relative speeds approaching that of light, relativity tells us that both time and distance alter their scales such that the speed of light cannot be reached. There’s the related issue of mass and energy heading to infinity.
Other questions a bit like this are sometimes asked, such as trying to reach absolute zero of temperature – it can't be done by any finite process. One could always hope there is something wrong with the theory, and try experiments to find out what. However, the evidence so far is strongly against it – even more so for thermodynamics than for relativity. Definitely don’t put any money on it!
Question 4
Can anything travel faster than the speed of light?
Prof Pethica: A slightly more complicated question than travelling at the speed of light. For example, the speed of light in a piece of material is generally lower than in vacuum. Therefore if a particle enters a material below vacuum light speed but above light speed in that material, it has to slow down. The energy it loses doing so appears as Cerenkov radiation. This can be readily observed.
Apart from that, there is no evidence for faster than light travel. Just as important, there is no evidence that information can be sent anywhere faster than light speed.
Question 5
Will it be possible to reach other planets that are capable of supporting life, so we can populate them?
Prof Pethica: The prospects for outside the solar system are not looking good. In theory it is possible, with sufficient continuous acceleration, to reach the stars, but there would be a problem of serious time dilation if you then returned to Earth. Same if you somehow hibernated.
The technology required for all that is not in sight at the moment and there are some very basic difficulties.
All this of course leaves aside the perhaps more important question - what about the life that might already be on those habitable planets...?
Question 6
This may seem like a silly question however I'll ask it anyway. Is there any danger in smashing particles together at near light speed?
Prof Pethica: It's very unlikely. The whole world is being bombarded (smashed into) all the time by large numbers of cosmic rays, many of which have much greater energies than anything we can produce in the laboratory, and yet we still seem to be here.
Question 7
In the Master of the Universe programme it was described that black holes gave off radiation as a result of the negative mass part of a particle/anti-particle pair being drawn into the black hole leaving its partner to rush off. But wouldn't something with negative mass be repelled by gravity rather than attracted?
Prof Pethica: Both particles and anti-particles have positive mass. These virtual pairs are produced by quantum fluctuations, an important property of the vacuum. There are no particles known to have negative mass, so the question of repulsion doesn’t arise.
There are theories about negative mass, first due to Bondi, but there is no evidence it applies to real world matter. Hawking showed that negative energy is required for closed timelike curves. (see The Future of Spacetime, Norton 2002) This is part of the reason why time machines are not going to happen. You can find out more on this at the usual encyclopaedic websites and search engines.
