• The Einstein mystery

    Playing with gravity

    Einstein’s theory of gravity has to contain some errors. But where are they? Eric Bergshoeff and his team have already been looking for years. Sometimes they find a small piece of the puzzle.

    in short

    Einstein presented his theory of general relativity about gravity precisely 100 years ago and it is still as solid as a rock, even though researchers know that it is not yet complete.

    The theory of gravity works when one uses it for large distances, but gives unworkable outcomes in the world of elementary particles. The quantum mechanics is not useable in the visible world.

    This also says something about the validity of our most important theories. Moreover, there are situations in which both theories are needed: in researching the big bang, for example.

    The theoretical physicists working with Eric Bergshoeff are looking for the Holy Grail: quantum gravity.

    One solution is string theory, but that is more of a calculation model and is not verifiable.

    Berghoeff’s PhD’s are modifying Einstein’s theory in ‘crazy’ conditions in an attempt to unravel the puzzle. Some calculate with a flat universe, while others look back to Newton’s theory.

    full version

    Reading time: 7 min. (1819 words)

    Do not come to Eric Berghoeff saying, ‘It’s been proven! Einstein was wrong’. The newspapers plaster that headline on their pages so often that he is no longer impressed. He is not even impressed with the messages about ghost particles which have been found in Delft, which Einstein did not want to recognize the existence of. They’re details of secondary importance.

    Einstein’s theory of general relativity which turned the world on its head precisely 100 years ago is as solid as a rock. ‘There is yet a crack to be found’, says Bergshoeff, half in admiration and half in frustration. ‘It is actually unbelievable. In 100 years, not one change has been made to the theory.’

    Adjustment is required

    He has searched his whole life – part of which he is presently spending as the director of the Van Swinderen Institute in Groningen – for a way in which he, a theoretical physicist, could adjust Einstein’s theory of relativity. Scientists are in agreement: it needs to be adjusted.

    Why? Because the theory of relativity does not always work and physicists are not happy about this. They want one model, one outline of reality. This is not the case currently. Not even the brain of the most brilliant scientist of all time could produce that.

    ‘Einstein’s theory works brilliantly on large distances, thus the distances out of the visible world’, says Bergshoeff. However, if you dive into the world of atomic particles, quarks, and Higgs boson, then gravity is not of much use as it is insignificantly small compared to the force in the atom.

    Not combinable

    Quantum mechanics should therefore be correct, you might say. That is also a theory which is admittedly extremely complicated and counterintuitive, yet it works inside the atom. This theory brings about the same problem, but then in reverse: quantum mechanics is of no use when working with large distances.

    That stings.

    Scientists could of course just shrug it off and use relativity theory when researching planets and stars, and quantum mechanics at the particle accelerator in CERN. In fact, that is what happens in practice, but that doesn’t sit well with the researchers.

    and gravity

    Einstein published his general relativity theory about gravity precisely one hundred years ago. Until that point, physicists worked with Newton’s laws of gravity, which stated that particles which had mass attracted other particles. Thus, the sun attracts the Earth and the Earth in turn attracts the moon.

    However, it was not completely right. The trajectory of Mercury, for example, showed a small deviation. Why was that? There was also another problem: the laws of Newton were not relativistic. Furthermore, all experiments were linked to the Earth and were therefore not generally applicable.

    Einstein tried a different approach. He introduced time as a fourth dimension and thus the concept of space-time. Using this, he could make all of his laws applicable generally. He then proposed that space-time was like a tightly stretched sheet. Mass makes a bend in the space-time, just like a billiard ball would make a dip in the sheet. Other bodies react to the curvature, like balls in a roulette game. If there is no mass, there is no curvature.

    However, if you apply Einstein’s theory to miniscule distances inside the atom, then the theory is not of much use. The gravity is simply not strong enough to influence the forces which govern the elementary particles.

    ‘It says something about the validity of our most important theories. Moreover, there are situations in which both theories are needed: in researching the big bang, for example, when all the mass in the universe was compressed into one dot the size of an atom, or in the research of black holes’, says Bergshoeff. In these exceptional circumstances, quantum mechanics is just as necessary as gravity theory, and then the whole thing falls apart. ‘It is an embattled marriage’, admits Bergshoeff. ‘The two theories are absolutely not compatible.’

    The Holy Grail

    The main problem is the representation of space-time. Gravity theory predicts a neat curvature. Quantum mechanics, however, sees it completely differently and comes up with a disorderly kind of space-foam which blows up all existing formulae.

    Bergshoeff and his team are thus searching for the Holy Grail: quantum gravity – a theory which can be used for the universe but also for the world of atomic particles.

    If he should succeed, he should go ahead and book a flight to Stockholm to pick up his Noble Prize. But as it goes with any research worthy of a Nobel Prize, it’s not easy. Furthermore, Bergshoeff will not be satisfied with just a theory. He wants one which can be verified.

    Because – let’s be honest – there is already a theory which connects the two theories: string theory. This theory proposes that the world is made of ten dimensions, most of which are too small to perceive. In those dimensions, small particles, envisaged as ‘strings’, move. These ‘strings’ are so small – much smaller than the smallest quark – that we do not notice them.

    Bergshoeff himself adjusted this theory already: operating on the idea that apart from the strings, there may also be tiny membranes, or ‘branes’. All of the membranes lie above the disorderly space-foam of quantum mechanics, like a fakir on a bed of nails. ‘And it works. The formulas do not blow up when you use string theory. The only problem is that string theory cannot be proved. It is a calculation model’, says Bergshoeff. ‘There is not one piece of proof that shows that nature actually makes use of it.’

    Everyone in clogs

    That proof is something Bergshoeff wants. But how on earth do you go about getting that? How do you correct Einstein?

    ‘The problem is that so much happens in the universe which we do not know about’, Bergshoeff says. ‘This is simply because we can only perceive a limited number of things. If you never went outside of the Netherlands, you would think that everyone wore clogs. Of course that is not true.’

    Bergshoeff refers to dark matter – which constitutes 22 per cent of the mass in the universe – which physicists have calculated does exist, but no one has ever witnessed. He also refers to the equally theoretical dark energy – comprising 74 per cent of the mass in the universe – which acts as a kind of elastic force that accelerates the expansion of the universe.

    ‘It has to be there, because our calculations are only correct based on that assumption. If they are particles which do not react to light and do not have an electric charge, we cannot detect them. That is disappointing, of course. We can only see four per cent of the universe’, says Bergshoeff. ‘Our eyes are focused upon the small piece of cake that we can see.’

    He and his team thus adjust and tune Einstein’s formulas in an attempt to find the weak spots. ‘Consider it as a dinky toy which we are taking apart’, he says. ‘We are trying to play with Einstein and see if something else could be done which would give more insight.’

    Dinky-toy universe

    His Ph.D. student Lorena Parra Rodrigues researched the gravity in a so-called ‘flat universe’. Parra – who received her Ph.D. last month – proposed a world of three dimensions: length, width and time. ‘It gives quite a lot of insight if you simplify your model’, she says. ‘Then, the math is more pliable. Consider it a toy model.’

    Bohr and quantum mechanics

    The theory of quantum mechanics came about around the same time as the general relativity theory. While Einstein’s theory deals with gravity, quantum mechanics deals with three other forces in physics: the electromagnetic force (the force that charged particles exert on one another), the strong force (which keeps the atomic nuclei together) and the weak force (which sees that atoms slowly expire).

    Quantum mechanics has two elementary ideas. Firstly, magnitudes, like energy, do not occur in random quantities, but in packages of ‘quanta’. Every distance or quantity can be expressed in multiples of quanta.

    Secondly, theory says that a particle has the properties of a wave, but that this property can never be measured at the same time. This means that you can never know where a particle is located or what it does. If you apply these ideas to space-time, you do not get Einstein’s tightly stretched sheet, but a kind of disorderly space-foam.

    In her dinky-toy universe, Parra focuses on graviton, the particle which ‘transfers’ gravity. ‘Although we have never measured it, we know that it has to exist.’

    According to Einstein, graviton does not have a mass. Parra decided to look at what happens if you suppose that it does. What did she find? The great differences of opinion between quantum mechanics and relativity theory about the amount of dark energy in the universe was suddenly much smaller.

    Another of Bergshoeff’s Ph.D.s, Thomas Zojer, is tinkering with gravity. He is doing this by ignoring Einstein for the moment and going back to Newton. ‘Newton’s experiments with gravity were dependent on an earthly coordinate system’, says Zojer. ‘As such, they are not generally applicable. The geometry to approach it differently did not exist then.’

    Gold pieces under the sand

    But that is different nowadays. So what would happen if you were to use Newton’s laws of gravity in the way that they are generally applied? ‘Then it would be possible to use gravity for other physics models’, says Zojer, ‘for instance models that describe the universe as a hologram.’

    That could then be used to gain more insight into the slippery matter. They are baby steps, these tiny puzzle pieces which Bergshoeff’s group is trying to fit into the bigger picture with each additional component bringing them that little bit closer to the solution to the mystery of gravity. Bergshoeff is no longer harbouring any illusions anymore that he – just as his illustrious predecessor and role model – can formulate a theory which will turn the world on its head again.

    Or can he?

    ‘You know, Einstein was the right man at the right time and at the right place. Yes, he was brilliant, but the time and the conceptualisation have to allow for such a theory to be formulated’, says Bergshoeff.

    Although it doesn’t look as though a breakthrough is at hand, that could quickly change. ‘It is as though you know that there is treasure hidden on an enormous beach’, he says. ‘Sometimes, everyone looks in the same direction and searches at the same spot. And then, there is one person who – using their intuition or something else – searches at a different spot and suddenly finds gold pieces just under the sand.’

    This month it has been exactly 100 years since Einstein formulated his theory of general relativity. Eric Bergshoeff will give a lecture on November the 17th at Studium Generale Groningen about ‘One hundred Years of Einstein.’