The Death of the Universe: Ghost Kingdom: Hard Science Fiction (Big Rip Book 2)

by Brandon Q Morris

  •Big Squeeze: If dark energy (which drives the universe apart) is increasing faster than the universe is expanding, the density of the universe would continue to increase. Eventually, space would become viscous and, finally, there would no longer be any possibility of movement for all eternity, and therefore no life.

  •Big Crunch: The universe eventually stops expanding, then it contracts again—a Big Bang in reverse, which would become a ‘Big Bounce’ if it is then followed by another expansion.

  •Big Freeze: The universe continues to expand, which causes its temperature to drop steadily until eventually there is no freely-available energy left. The particles and the world as we know it would stop moving, and in that moment time would also cease.

  •Heat Death: Similar to the Big Freeze, which would occur if the temperature throughout the universe approached a mean. In that case, too, the temperature differences that make life possible would be lacking.

  •Big Rip: The manner of death that scientists consider most likely is the ‘Big Rip.’ The expansion of the universe has been increasing measurably since about six billion years ago. This is due to dark energy, which we basically know nothing about. It possibly contains a component that scientists call ‘phantom energy.’ This has the property, if it even exists, of increasing the acceleration of the expansion. As a practical consequence of this scenario, everything, including the smallest building blocks of matter, will eventually be torn apart in a Big Rip. Based on this theory, Chinese researchers have come up with an estimate of when the end will occur.

  The computer simulation, fed with the known parameters of the current expansion of the cosmos and various unknowns, gives the universe at least another 16.7 billion years—which means it hasn’t even reached middle age yet. But it will become inhospitable sometime before that. About 32.9 million years before the Big Rip, the structure of the Milky Way will disintegrate. When the Earth leaves its orbit around the sun, we’ll have two months left before the collapse. Five days before the end, we’ll have to say goodbye to the Earth's moon. And 16 minutes before the end the Earth will explode.

  More about the Big Trick

  One of the possible scenarios for the death of the universe is the ‘Big Trick’ (see above). It’s based on the assumption that our universe is not in its default state, but in a metastable state, a bit like a ball that has rolled into a valley between two mountains. According to the classical view, it can’t be moved from its default state. Even if there is a deeper valley two mountains over, it would still have to roll back up the mountainsides by itself in order to reach the poorer state of potential energy in the deeper valley.

  However, quantum physics provides it with a shortcut: tunneling. In quantum physics terms, the ball is not just in the one valley where the observer just saw it. Rather, it forms a probability distribution across all valleys of the world. Of course, it has an extreme maximum in the place where it’s currently located—but, at least theoretically, it could suddenly appear in a deeper valley without any time passing. As a macroscopic, complex, and very heavy object, the chance of this is almost infinitely low. But it is greater than zero. If we only wait long enough (statistically longer than the age of the universe), we can safely observe this so-called phase transition. But statistically, of course, it could also occur the day after tomorrow.

  The universe is similar to the valley. Like its inhabitants, we consider the state of the vacuum, the vacuum energy, in the same way the inhabitants of a mountain valley consider its default state. But in fact, there is no factual reason why there should not be an even lower energy level, that an even deeper valley might exist somewhere. The Standard Model of particle physics also reaches this assumption. In fact, there may once have been such a phase transition—billionths of a second after the Big Bang. The result of this was that space filled up with the Higgs field. Elementary particles only acquired their mass through interaction with this field (via the Higgs bosons, which physicists are now almost certain they have found).

  How likely is a new phase transition? A working group at the University of Southern Denmark has published a paper dealing with this question. The researchers are primarily concerned with the question of how stable the Standard Model is, especially in terms of the order of magnitude of a Planck length. But we’ve known for a long time that the default state must be very close to the boundary between stability and instability. The Danish team has succeeded in systematizing and refining the mathematical foundations for diagnosis. A practical finding is that the universe is clearly much more on the unstable side than previously thought—significantly increasing the risk of a phase transition.

  However, this calculation is also burdened with considerable uncertainties. On the one hand, we know that the Standard Model can’t be complete—for example, regarding the neutrino mass and the dark matter and dark energy needed to explain the expansion of the universe. On the other hand, scientists say that such a phase transition would take longer than the universe has left to live. Whether the universe will die a cold death, or expire due to a catastrophic transition into its default state, remains far from certain.

  Dark matter + dark energy = liquid with negative mass?

  Physicists introduced the concept of dark matter after discovering, among other things, that galaxies don’t possess enough mass to explain their rotation. Dark energy, with its peculiar properties, is needed, for example, to explain the evolution of the universe in its infancy, when it must have suddenly had a tremendous growth spurt. Both concepts are summarized in the current model of the universe, known as the Lambda-Cold Dark Matter (ΛCDM) model.

  However, this model has a slight disadvantage. It doesn’t say anything about what dark matter and dark energy consist of. Nor have experimental physicists come any closer to an answer to this question in recent years. We would need a new kind of physics, but all that is yielded by the experiments is confirmation of the current understanding of physics.

  That could actually be good news, if it didn’t leave such a bitter aftertaste—because the universe appears to behave a little differently than what our physics predicts. Maybe a new model would help? That’s what physicists at Oxford University have proposed in the Astronomy & Astrophysics journal. Their model combines dark matter and dark energy into a substance with the properties of a liquid with negative mass, which therefore generates a negative gravitational effect. That is, everything is repelled by it.

  This negative mass, according to the theory, is continuously generated as the universe expands, and emulates the effects of dark energy. The negative mass would also simultaneously create the galactic rotation we observe in practice and thereby replace dark matter. In this new model, the positive mass of the universe is swimming, so to speak, in a vast sea of negative mass, at the bottom of which is a spring out of which new negative mass flows.

  The new theory can probably be tested with the new international radio telescope, the Square Kilometer Array (SKA).

  Can mass be negative?

  The simplest things are often the most difficult to explain. Mass, for example. Everyone has an intuitive understanding of it. “What’s heavier? A kilo of feathers or a kilo of lead?” Only preschoolers fall for this riddle. And yet the concept of mass is only vaguely understood, even by physicists. Electrical charge made it much easier for us. Since the discovery and proof of the Higgs mechanism, we know what mass is made of. But could something like negative mass exist?

  If we look out into the universe, analyze its behavior, and attempt to explain it with the current state of our knowledge, then the answer is that there has to be negative mass. This is because the accelerating expansion of the universe leads us back to ‘dark energy,’ a mysterious field with negative energy density, to which we must attribute a negative mass density using Einstein’s formula. So there must be ‘things’ whose mass in kilograms has a negative value. At present, however, we can’t describe them as any more than ‘things.’ But at least we can now think about how such
a negative mass would behave, also in relation to positive mass. The good news is that both would be well tolerated because this relationship has nothing to do with the matter-antimatter duality. Antimatter has a positive mass!

  Einstein’s equations reveal that positive mass attracts other positive mass, but also negative mass. Negative mass, however, repels both negative mass and positive mass. The result is that two equal masses with different algebraic signs would produce a constant acceleration of the entire system in the direction of the positive mass. The system would become faster and faster without any external influence, but would have a constant total momentum of 0 and would thus not violate any of the conservation laws (runaway motion). In a gas consisting of particles of negative and positive mass, the positive portion would increase its temperature to infinity, but the negative portion would have to reach negative temperatures.

  It gets especially complicated when two equal masses with different algebraic signs and momentum meet, thus causing a collision. If they are both in the same place, they would have to extinguish one another without leaving any mass (or energy) behind. But that would violate the law of conservation of momentum. So, masses with different algebraic signs can only coexist in the form of runaway motion, which leads to the assumption that there can be no negative mass after all. But what does the expansion of the universe suggest?

  It's complicated, that much is clear. The nature of dark energy is still wholly unexplained. Being able to produce it in a lab in order to research it seems utopian at the moment. Therefore, the next best alternative is to be able to work with systems that behave as though they have a negative mass. This is standard practice for other physical quantities. Astronauts aboard the ISS are investigating the effects of microgravity, although, being so close to the Earth, they are attracted to Earth only slightly less than they would be on its surface. It’s just that they don’t feel the gravitation because they are in free fall together with the space station. If there was really no Earth gravity there, the ISS would spin out into space.

  A similar model has been generated in a laboratory by Washington State University researchers. Their paper was published in Physical Review Letters and their focus is the aspect of mass called inert mass—that is, mass as a proportional factor between force and acceleration. Typically, in the Newtonian formula F=m*a, force (F) and acceleration (a) have the same direction. Understandably, a negative mass would cause the acceleration to reverse. If you hit a billiard ball with negative mass, it would move in the direction exactly opposite to your hit. In other words, the ball would move towards you.

  To reproduce such a system in a laboratory requires some effort. The researchers cooled a cloud of about 10,000 rubidium atoms to temperatures near absolute zero. The atoms are then in a default state in which they are no longer distinguishable from each other and become a Bose-Einstein condensate (BEC). This state can be described by a common wave function, not by the movement of individual particles.

  Then comes the real feat. Using lasers, the researchers create a kind of virtual container for the BEC, with special properties, which the atoms can break out of only with certain behavioral patterns—they manipulate the dispersion relation under which the particles of a common wave function can be dispersed (a rough comparison would be the effect that occurs when you observe a teaspoon in a glass of water—it looks kinked). In fact, the superfluid behaves exactly as expected, as though it has an effective negative mass, and moves counter to the direction of an outside impulse.

  Note the word ‘effective,’ which major international media omitted when reporting on the experiment. The entire apparatus has not become a single microgram lighter, just as the ISS can’t switch off gravity. So, negative mass has not been created, but a system has been created, which under certain circumstances acts as though it has negative mass. This is still very helpful and does not diminish the researchers’ efforts, as it allows us to study many properties of negative mass that we would otherwise have no access to.

  The universe is mostly empty

  The question of what empty space is, and whether such a thing even exists, has preoccupied scientists for centuries. According to Aristotle, space beyond the moon was filled with ‘quintessence,’ Latin for ‘fifth element.’ Unlike fire, water, earth, and air, this ‘ether’ was the only element considered to be everlasting. Later it was the long-distance effect—for example, of light—that demanded a medium of transport to fit with the ideas of classical physics. For instance, Huygens, who formulated one of the first wave theories of light, assumed there was a light-ether that permeated solid matter as well as space, through which light waves spread out.

  It wasn’t until the theory of special relativity (TSR) that Einstein could finally denounce ether, because he moved away from the idea of absolute space. For a short time the vacuum was regarded as completely empty, even if space in terms of the general theory of relativity naturally possesses physical properties, that is, it’s not ‘nothing.’ The universe was initially imagined as being static. However, when its expansion became evident, a kind of vacuum energy was needed for a suitable solution to the equations of the GTR, and this was given the name ‘cosmological constant.’

  If they weren’t already, things got complicated with the introduction of quantum field theory. On the smallest scale, quantum physics requires—and this has been successfully proven—that subatomic particles must constantly be jumping into existence out of nowhere, only to say goodbye again in the shortest possible time, so that on average the conservation of energy is maintained. Although these virtual particles exist only briefly, their short life naturally contributes to the energy content of the vacuum. However, if you add up the energy of all virtual particles at any given time, you get a value of 1.4*10128 GeV/m3 (10128 is 1 with 128 zeros). But what mean vacuum energy would space have to contain for the universe to expand as it does in practice? Experiments have confirmed this to be about 4 GeV/m3. So there are more than 100 orders of magnitude between theory and practice!

  That’s the problem with the cosmological constant—it’s an open question, and you could hardly find a more open one. The problem is that the vacuum has a far more complicated structure than one might naively assume just by looking into the emptiness of space. It shimmers and blows bubbles, it changes depending on your perspective. The electromagnetic vacuum behaves differently than the vacuum of gravitation, which differs from the vacuum of the weak nuclear force (which can be thought of as a condensate of non-located Higgs particles distributed over the whole universe) and the vacuum of the strong nuclear force (which would be a lake of quark-gluon matter in its default state).

  You can imagine it like a lake filled with various liquids. The vacuum is the surface of the lake. Matter is the wave-like excitation that happens when you throw in marbles of different sizes. What the waves actually look like depends on both the mass of the marble thrown into the lake and the viscosity of the lake. A lake of water undergoes excitation that’s different from a lake of oil, tar, or Jell-O. Now all you have to do is make a tiny mental leap and imagine the lake as a quantum physical overlay of all possible variants of the lake, which are also constantly changing from one to the other—then you have a realistic idea of the structure of the vacuum. Done? Congratulations! I always give up at Jell-O, and go to the fridge.

  The good news is, to reasonably anticipate the evolution of the universe, we don’t need to know the exact structure of the vacuum. It’s enough to find a sufficiently accurate model, in terms of measurement accuracy, to describe past and present. Then we can assume that statements made by such a model about the future are also reliable. And physicists are actually using this approach in a meaningful way. For example, in a paper in the Astrophysical Journal, three Spanish researchers are particularly concerned with cosmological models that, unlike the standard ΛCDM (Lambda CDM) model of cosmology, assume a vacuum energy density that changes over time, dependent on the Hubble ‘constants.’

  In some cases,
such ‘running vacuum’ models even assume that the gravitational constant G changes—or they exclude conservation of mass altogether. The current work of these Spanish scientists is not concerned with discussing the physical stability of these models. Instead, they simply take the given formulas and parameters and compare them with actual values, according to the motto that a good theory is not one that we understand, but one that describes reality.

  The result is encouraging for the theorists behind the running vacuum models. The tested models with variable cosmological ‘constants’ are clearly superior to the standard theory in terms of rendering reality as it looks according to our own measurements. However, the comparison is still not accurate enough to give a definitive result. Therefore, scientists are hoping for more accurate measurements of the parameters they use.

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  Excerpt: Mars Nation

  Sol 3, NASA base

  The sun floated right above the horizon in a rosy sky. Lance squinted at it. It looked much smaller from here than it did from Earth, but its light could still blind him if he gazed right into it. After a few more arc minutes around the sun, the sky shifted to blue. Sharon, the pilot whose studies had also included meteorology, had told him about this, but he hadn’t believed her. He needed to apologize to her, even though the others knew by now that he was one of those who had to see such things with his own eyes.

  “Everything alright?” he heard Mike’s voice say over his helmet radio.

  “Yes, Commander. It’s very romantic.”