Cosmology and our View of the World
Asymmetry of Time I
Lead: Eddie LaVilla & Eric McDonald
Summary by Brianna Jean
Imperfection and the Weirdness of the Quantum World
M. Gleiser “Tear at the Edge of Creation” Chapters 11-16
The presenters of this topic, Eddie LaVilla and Eric McDonald, started by giving a general historical progression of the scientific view of the world from a geocentric universe, which perfectly supported creation myths that humans have believed for thousands of years, to the heliocentric model of the universe all the way to the view under the modern scientific theory known as the Big Bang theory. As a species, we are naturally interested in understanding where we came from and how we fit into the universe. Historically, many of our explanations have been influenced by our habitats and the things that we experience. They often involve some theory of divine Creationism. Scientific inquiries have often negated these Creationist stories in whole or in part and have found different ways to try to explain the origin of the universe; most by extrapolating time backwards towards some beginning. Einstein’s discovery in the early twentieth century that light is both a wave and a particle is just one example that shows that our historically simple conceptions and explanations of the universe do not come close to uncovering the complexities of the reality we live in.
Eddie and Eric then went on to describe a second topic of space and time. In 1965 Arno A. Penzias and Robert W. Wilson discovered cosmic background radiation that was consistent with predictions from the Big Bang theory. The data implied that the universe was once very hot and dense. At the predicted temperature, neither atoms nor their basic constituents could exist. The constituent particles of atoms would form one millionth of a second after the expansion of the universe. As the universe expanded and cooled, the nuclei of atoms would be kept apart by radiation kicking neutrons away from protons until the radiation became weak enough for the strong nuclear force to overcome the interference, and bind the particles into nuclei. After approximately 380,000 years of expansion, the universe would have cooled enough so that electrons could combine with nuclei to form atoms. As space continued to expand, electromagnetic forces bonded atoms together to form molecules and the force of gravity caused atoms to conglomerate forming stars; eventually the universe we now know formed from the universe’s expansion. It is only through observation of radiation that we have extrapolated a history of our universe at all. It is only through this idea of expanding space that we have a concept of time moving asymmetrically forward. Time is not the only quantity that moves in one direction; entropy also moves in one direction, tending towards disorder. Could time and entropy be linked? Is entropy just a result of single-directional time?
Eddie’s and Eric’s focus then shifted to the phenomenon that makes all of this observable, light. As humans, we can see only a small part of the spectrum of electromagnetic radiation, the part known as visible light. Light is an electromagnetic wave that does not need a medium to propagate at its constant speed of 300,000 km/s. Maxwell was able to unify the electric and magnetic forces into the electromagnetic wave that is light. Einstein tried to further this unification by unifying all the then-known forces: gravity, electricity, and magnetism, but he was unsuccessful. He did, however, prove that light was not only a wave, but also a particle known as a photon. This suggested a wave-particle duality, a principal concept in Quantum Mechanics. In the world of Quantum Mechanics, it is impossible to know simultaneously the velocity and position of electrons, everything is in a constant state of flux due to electron jittering. This means that we can only predict where things will be probabilistically; we can only know where something is or how fast it is going, never both at the same time, thus there are no certain predictions in the quantum world, only probabilistic ones.
After several corrections to the presenters’ brief outline by Eberhard Möbius and Willem deVries, the conversation moved from general background to the discussion of several of the underlying concepts of Quantum Mechanics to time and to our perception of time. The following ideas were suggested by various individuals in the classroom in a free-flowing style. They are not presented here in the order in which they surfaced, but in an order that groups them into more lucid and connected topics.
Perhaps it is best to start with the most intuitive principle of time. Time moves in one direction: forward. Time began with the expansion of the universe, and shares an unbreakable tie with space. We cannot conceive of time in a classical physics sense when the universe would have been quantum-sized; at this point we have no idea of how space-time might have worked. However, from the moment that the universe began expanding, if we accept the Big Bang theory as a premise, we can make conjectures that time has only moved in a forward direction. One idea that was noted here, was the idea that entropy only moves in one direction as well; things seem to naturally tend towards disorder, a single-directed flow of time seems necessary for this principle to hold any truth.
Another idea that seems to be tied to an asymmetric movement of time is cause-and-effect relationships. Time allows us to see a supposed connection between things and the things that follow them. If time moved in both directions, it would be hard to determine what caused what. Someone supposed that perhaps all time could be co-existent in some other dimensionality, referencing Rob Bryanton’s video that has been floating around the web entitled, “Imaging the Tenth Dimension.” This video suggests that there are multiple universes that exist simultaneously. In each universe is a different course of events such that any series of events exists and occurs in a single universe. At some dimensional level all time co-exists even if we can only experience it in individual instants. Could we be forever in all instances of our existences, but be trapped to perceive only one instant at a time, or is the idea of a co-existent time absurd in-itself? What is time but sequential instances strung together in our perceptions?
The idea of space and time being tied together is a result of Einstein’s Theory of Relativity where space and time change based on the relative perspective of the observer to its reference point. Einstein’s Theory of Relativity is based on the premise that the speed of light and all the physical laws of observers in different reference frames are the same. From the constant speed of light we can observe that if an object moves through space at a higher speed than the reference frame, light travels the same speed, but a shorter distance. For this to be consistent, time must be stretched. Möbius drew a very helpful diagram to aid this concept, showing the increased length due to the movement through space. A similar diagram follows:
Above is depicted a rocket traveling at some speed that is a substantial fraction of the speed of light. The first part of the diagram shows the path of light reflected at a mirror from the perspective of the rocket. An observer in the rocket would see the light hit the mirror and bounce back in a straight path. A stationary observer outside of the rocket would see the second part of the diagram; from the stationary reference frame the light travels a larder distance than it does in the moving reference frame. In order for this to be true and for the speed of light to be constant, time must pass slower in the moving reference frame than in the stationary reference frame.
Another helpful tool in understanding the implications of space-time that we discussed is the Twin Paradox. This paradox presents two twins, one who stays on Earth, and one who travels many years in a high-speed rocket. When the twin that has traveled comes home after experiencing a contraction of time, he is much younger than the twin that remained on Earth. This gedanken experiment further helps us understand the concepts and implications of special relativity and time dilation.
Another hypothetical implication of the space-time connection is the potential to travel through time. Space and time are bent by gravitational fields. If an object is dense enough, the gravitational fields become so strong that not even light can escape, this is appropriately named a black hole. A black hole bending space with the right geometric orientation could hypothetically result in a wormhole in which one could travel through a sort of tunnel to a different time. The problem is, in order for a worm hole to stay stable and open, matter much stronger than the matter of our Earth is necessary. This hypothetical matter, sometimes referred to as “unobtainium,” has not been discovered yet. However, the hypothetical possibility of time travel resulted in a whole other sort of topic. If time travel were possible, would we know it? If someone went back in time would he or she make the same choices over again? If they could make different choices how would these choices snowball in their effect or lack of effect on the universe on a broader scale?
Removing ourselves from the hypothetical outcome of how time travel would affect the universe, are there ways in which we can mentally time travel or experience different perceptions of time? Prophesy and dreams that tell of future events seem to be some sort of time travel. We can see into what might have happened or what will happen. Is there any sort of significance or meaning to these time travels? The general conclusions seemed to be that these are instances very much separate from the concept of time, but rather related to our perception of time, and thus are psychological phenomena. There is a difference between time and the perception of time, as deVries noted several times throughout the discussion. This distinction became a central theme in the conversation. Möbius even noted that in Greek there are two different words for time; one a qualitative property (horos) and one a quantitative property (chronos). Time in a scientific sense is very different from our daily experiences with time.
The way in which we most often think of time is as forward moving with some objective “speed.” Even if we can observe that time dilates with motion through space, from our daily perspectives, this is not how we think of time. It seems our experiences of time can be divided into our concept of time and our perception of time. Our daily concept of time is not as something that can change; for the most part we are not moving at speeds fast enough for an effect to be significant. While time from any objective reference point in space-time is constant, our clocks all represent the same time; our perception of time passing is subjective and arbitrary. While the length of a day is based on something physically meaningful, the number of hours in a day is arbitrarily set. Sleep also affects our perception of time. When we awake, time either appears to have passed so quickly we don’t remember it passing at all, or our dreams were so realistic and eventful that it seems far too much has happened for the amount of time that has passed according to our clocks. Athletes seem to notice a similar phenomenon; time passes quickly while they are performing. They get so engrossed in “the zone,” that they hardly realize time is passing at all. In general, our attentiveness and interest greatly seem to affect our perception of time. Another interesting phenomenon is the perception of the speed of the passing of time relative to one’s age; the older one gets, the faster time seems to pass. In the course of forty years one year seems much shorter than in the course of four years.
The overall direction of this topic took many spins centering around time as an asymmetrical movement, its objective relativity depending on reference frame, the idea of time travel, and the subjectivity of our perception of time within our constant concept of it. Time is a topic which is so relevant to our daily lives, but is more complicated than we might perceive it to be, especially if we try to imagine what it may have been like before the universe followed its current rules; the time when Quantum Mechanics may have ruled time. We have again bumped up against an opaque wall in the history of the universe; we are forever limited, kept from looking directly over it, and scientific discoveries still cannot give us enough insight to even glean what might be on the other side.