You are currently browsing the tag archive for the ‘relativity’ tag.

It is not often that we think of events as isolated incidents separated by a vast divide in both physical and virtual distance. In our day to day existence with near instantaneous methods of communication and a pervasively global information network, significant events are easily taken note of. But when the distance separating the event from the recipient exceeds our Earthly bounds, an interesting phenomenon occurs. Even on the scale of the solar system, light from the Sun takes approximately 8 minutes to reach our sunny skies here on Earth. If the Sun happened to go supernova, we would have no acknowledgment of the fact until some 8 minutes after the event actually occurred. While not completely revolutionary, this concept has deeper ramifications if the distances are again increased to a Universal scale.

While we are accustomed to thinking of light as travelling at a fixed speed limit, it is not often that one thinks of gravity as a force that requires time to cross intergalactic distances. But indeed it does. Gravity waves propagate at the speed of light; slight perturbations on the surfaces of incredibly massive objects (eg neutron stars or binary star systems) act as the catalyst for these disturbances. Unimpeded by objects, gravity waves are able to pass through the Universe without effect. They act to warp the nature of spacetime, contracting and expanding distances between objects as the wave passes through that particular locality.

Here on Earth, information is similarly transferred quickly along the Internet and other communication pathways at an average of close to the speed of light. Delays only arise when traffic is heavy (pathways severed, technical problems, increased use). As the distances involved are relatively small in comparison to the speed of the transfer, communication between two points is practically instantaneous. But what if we slow down the speed of travel? Imagine the event occurs in an isolated region of desert. The message can only be transmitted via a physical carrier, thus mimicking the vast distances involved in an interstellar environment. Observer B waiting to receive the message thus has no knowledge of what has happened until that message arrives.

Revisiting the scenario of the Sun exploding, it seems strange that mammoth events in the Universe could occur without our immediate knowledge. It is strangely reminiscent of the Chinese proverb; does a falling tree make a sound if no one is around to listen? Cosmic events are particularly relevant in this respect, as they most certainly do have immense ramifications (‘making a noise’). If the Universe suddenly collapsed at the periphery (unlikely but considered for the purposes of this exercise), our tiny speck of a planet would not know about it until (possibly) many, many millions of years. It is even possible that parts of the distant Universe have already ‘ceased to exist’; the fabric of time and space from the epicentre of this great event expanding like a tidal wave of doom. What does this mean for a concept of Universal time? Surely it must not be dependent upon physical reality, for if it did, surely such a catastrophic event would signal the cessation of time across the entire cosmos. Rather, it would be a gradual process that rushes forth and eliminates regions of both space and time sequentially. The final remaining island of ‘reality’ would thus act as a steadily diminishing safe haven for the remaining inhabitants of the cosmos. Such an event would certainly make an interesting science-fiction story!

Einstein became intimately aware of this universal fact of locality, making it a central tenet in his grand Theory of Relativity. He even offered comments regarding this ‘principle of locality’ (which became a recognised physical law);

“The following idea characterises the relative independence of objects far apart in space (A and B): external influence on A has no direct influence on B; this is known as the Principle of Local Action, which is used consistently only in field theory.”

A horribly simplified description of relativity states that what I experience is not necessarily the same as what you will experience. Depending on how fast you are travelling and in what direction relative to myself (taking into account the speed and direction at which I am travelling), our experience of time and space will differ; quite markedly if we approach the speed of light. Even the flow of time is unaffected, as observers aboard objects travelling at high velocities experience a slowing notion of chronicity compared to their colleagues. It would be intriguing to experience this phenomenon first hand in order to determine if the flow is psychologically detectable. Perhaps it would be experienced as an exaggerated and inverted version of the overly clichéd ‘time flies when you’re having fun’.

Locality in Einstein’s sense is more about the immediate space surrounding objects rather than causes and their effects (although the two are undoubtedly interrelated). Planetary bodies, for instance, are thought to affect their immediate surroundings (locality) by warping the fabric of space. While the metaphor here is mainly for the benefit of visualisation rather than describing actual physical processes, orbiting bodies are described as locked into a perpetual spin, similar to the way in which a ball bearing revolves around a funnel. Reimagining Einstein’s notion of relativity and locality as causality (and the transmission of information between two points), the speed of light and gravity form the main policing forces in managing events in the Universe. Information can only travel some 300,000 km/s between points, and the presence of gravity can modify how that information is received (large masses can warp transmissions as in gravitational lensing and also influence how physical structures interact).

Quantum theory adds to the fray by further complicating matters of locality. Quantum entanglement, a phenomenon whereby an effect at Point A instantaneously influences Point B, seems to circumnavigate the principle of locality. Two points in space dance to the same tune, irrespective of the distances involved. Another quantum phenomenon that exists independently of local space is collapsing wave functions. While it is currently impossible to affirm whether this ‘wave’ actually exists and also what it means for the nature of reality (eg many worlds vs Copenhagen interpretation), if it is taken as a part of our reality then the act of collapse is surely a non-local phenomenon. There is no detectable delay in producing observable action. A kicked football does not pause while the wave function calculates probabilities and decides upon an appropriate trajectory. Likewise, individual photons seem just ‘know’ where to go; instantly forming the familiar refraction pattern behind a double-slit grating. The Universe at large simply arranges its particles in anticipation of these future events instantaneously, temptingly inviting notions of omniscience on its behalf.

Fortunately, our old-fashioned notions of cause and effect are preserved by quantum uncertainties. To commit the atrocious act of personifying the inanimate, it is as though Nature, through the laws of physics, protects our fragile Universe and our conceptions of it by limiting the amount of useful information we can extract from such a system. The Uncertainty Principle acts as the ubiquitous protectorate of information transfer, preventing instantaneous transfer between two points in space. This ‘safety barrier’ prevents us from extracting useful observations regarding entangled particles without the presence of a traditional message system (need to send the extracted measurements taken at Point A to Point B at light speed in order to make sense of the entangled particle). When we observe particles at a quantum level (spin, charge etc) this disturbs the quantum system irrevocably. Therefore the mere act of observing prevents us from using this system as a means of instantaneous communication.

Causality is still a feature of the Universe that needs in-depth explanation. At a higher level is the tireless battle between determinism and uncertainty (free-will). If every event is predetermined based on the collisions of atoms at the instant of the Big Bang, causality (and locality) is a moot point. Good news for reductionists whom hope to uncover a fundamental ‘theory of everything’ with equations to predict any outcome. If, on the other hand, the future really is uncertain, we certainly have a long way to go before an adequate explanation of how causality operates is proposed. Whichever camp one claims allegiance, local events are still isolated events whose effects travel at a fixed speed. One wonders what the more frustrating result of this is; not having knowledge about an important albeit distant event or realising that whatever happens is inevitable. The Universe may already have ended; but should we really care?

Advertisements

In the first part of this article, I outlined a possible definition of time and (keeping in touch with the article’s title) offered a brief historical account of time measurement. This outline demonstrated humanity’s changing perception of the nature of time, and how an increase in the accuracy with which it is measured can affect not only our understanding of this phenomenon, but also how we perceive reality. In this article I will begin with the very latest physical theory explaining the potential nature of time, followed by a discussion on several interesting observations concerning the fluctuations that seem to characterise humanity’s chronological experience. Finally, I hope to promote a hypothesis (even though it may simply be stating the blatantly obvious) that the flow and experience of time is uniquely variable, in that the concept of ‘absolute time’ is as dead as the ‘ether’ or absolute reference point of early 19th century physics.

Classical physics dominated the concept of time up until the beginning of the 20th century. In this respect, time (in the same vein as motion) as having an ‘absolute’  reference point. That is, time was constant and consistent across the universe and for all observers, regardless of velocity or local gravitational effects. Of course, Einstein turned all this on its head with his theories of general and special relativity. Time dilation was a new and exciting concept in the physical measure of this phenomenon. Both the speed of the observer (special relativity) and the presence of a gravitational field (general relativity) were predicted to have an effect on the passage of time. The main point to consider in combination with these predictions is that by the very nature of the theory, relativity insists that all events are relative, or change with perspective, in respect to some external observer.

Consider two clocks (A and B), separated by distance x. According to special relativity, if clock B is accelerated to a very high speed (at least 30,000km/s for the effects to become detectable), time dilation effects will come into play. In effect, relative to clock A (which is running on ‘normal’ Earth time), clock B will be seen to run slower. An observer travelling with clock B would not notice these effects – time would continue to pass normally within their frame of reference. It is only upon return and the clocks are directly compared that the inaccuracy becomes apparent. Empirically, this effect is well established, and offers an explanation as to why muons (extremely short-lived particles) are able to make it to the Earth’s surface before decaying. Cosmic rays slam into the Earth’s atmosphere at high speed, producing sufficient energy when they collide with molecules for the generation of muons and neutrinos. These muons, which normally decay after a distance of 0.6km (if stationary/moving slowly), are travelling so fast that time dilation effects act to slow down the radiological emission process. Thus, these particles survive much longer (penetrating some 700m underground) than normal.

General relativity also predicts an effect on our perceptions of time. Objects with large mass produce gravitational fields, which in turn, are predicted to influence time by slowing down its perceived effects in proportion to the observer’s proximity to the field. Clock A is on the Earth’s surface, while Clock B is attached to an orbiting satellite. As Clock B is further from the centre of the Earth, the gravitational field at a lower potential, that is, it is weaker and exerts less of an effect. Consequently, the elapsed time at B (relative to Clock A) will be shorter (ie, Clock B is running faster). Again, this effect has been tested empirically, with clocks on board GPS satellites forced to undergo regular adjustments to keep them in line with Earth-bound instrumentation (thus enabling accuracy in pinpointing locations). Interestingly, the effects of both types of dilation are additive; the stronger effect wins out, resulting in either a net gain or loss of time. Objects moving fast within a gravitational field should then experience both a slowing down and speeding up of time relative to an external observer (this was in fact recorded in an experiment involving atomic clocks on board commercial airliners).

Frustratingly, the physical basis for such dilation seems to be enmeshed with the complicated mathematics and technical jargon. Why exactly does this dilation occurs? Descriptions of the phenomenon seem to lack any real insight into this question, and instead proffer statements to the effect of ‘this is simply what relativity predicts’. It is an important question to ask, I think, as philosophically, the question of ‘why’ is just as important as the empirical ‘how’, and should follow as a natural consequence. By probing the meta-physical aspects of time we can aim to better understand how it can influence the human sensory experience and adapt this new-found knowledge to practical applications.

Based on relativity’s notion of a non-absolute framework of time, and incorporating the predictions of time dilation, it seems plausible that time could be reducible to a particulate origin. The field of quantum physics has already made great headway in proposing that all matter acts in a wave-particle duality; in the form of waves, photons and matter travel along all possible routes between two points, with the crests and troughs interfering with, or reinforcing, each other. Similar to the double slit experiment (light and dark interference pattern), only the path that is reinforced remains and the wave collapses (quantum de-coherence) into a particle that we can directly observe and measure. This approach is know as the ‘sum over histories’ hypothesis, proposed by Richard Feynman (which also opens up the possibility of ‘many worlds’; alternative universes that branch off at each event in time).

In respect to time, perhaps its re-imagining as a particle could explain the effects on gravity and velocity, in the form of dilation. One attempt is the envisaged ‘Chronon’, a quantised form of time which disrupts the commonly held interpretation of a continuous experience. This theory is supported via the natural unit of Planck Time, some 5.39121 x 10ˆ-44 seconds. Beyond this limit, time is thought to be indistinguishable and the notion of separate events undefinable. Of course, we are taking a leap of faith here in assuming that time is a separate, definable entity. Perhaps the reality is entirely different.

Modern philosophy seems to fall over when attempting to interpret the implications of theoretical physics. Perhaps the subject matter is becoming increasingly complex, requiring dedicated study in order to grasp even the simplest concepts. Whatever the reason, the work of philosophers has moved away from the pursuits of science and towards topics such as language. What science needs is an army of evaluators, ready to test their theories with practical concerns in mind. Time has not escaped this fate either. Scientists seem content, even ‘trigger happy’ in their usage of the anthropic principle in explaining the etiology of their theories and any practical inquiry as to why things are the way they are. Basically, any question of why evokes a response along the lines of ‘well, if it were any different, conditions of the universe would not be sufficient for the evolutions of intelligent beings such as ourselves, who are capable of asking the very question of why!’. Personally, this approach does make sense, but seems to have the distinct features of a ‘cop-out’ and circularity; alot of the underlying reasoning is missing which prohibits deeper inquiry. It also allows theologians to promote arguments for the existence of a creator; ‘god created the universe in such a way as to ensure our existence’.

What has this got to do with time? Well, put simply, the anthropicists propose that  if time were to flow in a direction contrary to that which is experienced, the laws of science would not hold, thus excluding the possibility of our existence as well as violating the principles of CPT symmetry (C=particle/antiparticle replacement, P=taking the mirror image and T=the direction of time). Even Stephen Hawking weighs in on the debate, and in his Brief History of Time, proposes the CPT model in combination with the second law of thermodynamics (entropy, or disorder, always increases). The arrow of time, thus, must correspond to and align with the directions of these cosmological tendencies (universe inflates, which is the same direction as increasing entropy, which is the same as psychological perceptions of time).

So, after millenia of study in the topic of chronology, we seem to be a long way off from a concrete definition and explanation of time. With the introduction of relativity, some insights into the nature of time have been extracted, however philosophers still have a long way to go before practical implications are expounded from the very latest theories (Quantum Physics, String Theory etc). Indeed, some scientists believe that if a grand unified theory is to be discovered, we need to further refine our definitions of time and work backwards towards the very instant of the big bang (under which it is proposed that all causality breaks down).

Biologically, is time perceived equally among not only humans but also other species (animals)? Are days where time seems to ‘stand still’ sharing some common feature that could support the notion of time as a definable physical property of the universe (eg the Chronon particle)? On such days are we passing through a region of warped spacetime (thus a collective, shared experience) or do we carry an internal psychological timepiece that ticks to its own tock, regardless of how others are experiencing it? When we die is the final moment stretched to a relative infinity (relative to the deceased) as neurons loose their potential to carry signals (ala falling into a black hole, the perception of time slows to an imperceptible halt) or does the blackness take us in an instant? Maybe time will never fully be understood, but it is an intriguing topic that warrants further discussion, and judging by the surplus of questions, not in any hurry to reveal its mysteries anytime soon.

Time; the fourth dimension, inexplicably linked with space and dynamic in nature. According to Einstein and backed up by decades of empirical research, time is a variable phenomenon. This seems contrary to common belief as we often represent time as a pillar of stability, marching inevitably forwards and unwaveringly ticking away. This ‘inevitability’ of time has lead to the attachment of negative connotations, including themes of death and the ‘running out of’ time itself. As our society tends towards briefer periods of meaningful interaction and longer periods of unpleasant activities (work, commuting, queuing) it seems as though attitudes towards time are most favourable when it is ‘running fast’, thus minimising mental stress and anguish (reducing the perceived waiting/unproductive period). To this effect, time has been described as ‘the fire in which we burn’; a finite (at least in terms of human lifecycles) feature of our universe that is personified into some sort of omnipotent adversary. It is my intent, through the medium of a two-part article, to firstly present a condensed and brief history of the physical representations of time followed by the current understanding of this phenomenon and how it relates to everyday experience.

Humankind has been fascinated by time ever since the dawn of consciousness and self-directed thought. Exemplified and measured initially through the patterns and cycles exhibited by nature, time was quickly utilised as both a tool and a catalyst for philosophical thought. Time is the canvas upon which causes and effects occur. Without it, there would be no history, no future, only unconnected moments blended into one almighty chronometric experience. In a timeless universe and provided the intelligent observer was also given the gift of immortality, they would similarly experience both the birth and death of the universe in an instant; non-locality would be universal (time to travel between points would be instantaneous as there would be no reference against which to measure its passing). In short, the agent would be a god. But of course, this is not the case. We tend to think about time in the infintesimally short periods that correspond to the duration of the average human lifespan – 70 to 80 years. Ironically, the thing that we most wish would ‘hurry-up’ is only hastening our own non-existence (in the form of death).

Time fascinated early civilisations (and undoubtedly the groups of nomadic hunter gatherers that preceded them). They constructed vast, complicated monuments and invested much time and effort creating increasingly complex tools to measure the passage of time. Our ancestors realised that in order to measure time, the most important component needed is an objective, regular cycle. Naturally occurring examples of this were plentiful; seasonal changes in foliage signaled the changing of climate and food availability, and tracking the sun and other astronomical bodies in the sky could be used to measure the period of day and night. Water-powered clocks were perhaps the first timepieces that were independent of astronomical intervention (eg the sundial and yardstick). These devices worked by harnessing the regularity of flowing water. Quite complex additions to the basic flow such as gears, weights and threaded screws allowed a constant source of energy (water flow) to power timing components of the clock (filling up containers, raising pointers, turning wheels and gears). Quite quickly, the need for increasingly accurate devices to quantify time acted as a momentum for technological development in this area. Galileo (and Huygens) are credited with creating the first of such devices; a timepiece powered by the harmonic motion of a mass connected to a central pivot point via string. This improvement introduced more accurate timepieces, however they still lacked practicality. Like the water clocks before them, pendulums were bulky, unreliable over long time periods and required stability in order to function. These issues, coupled with a desperate need to improve the accuracy of marine navigation spurred John Harrison on to create the first purely mechanical and portable clock. The problem of nautical accuracy stemmed in part from the lack of a reliable method of keeping time. With an accurate timepiece and heading (provided by the compass) navigators could keep better track of the vessel and utilise the method of longitude/latitude to plot complex courses through the oceans. Designed specifically for the rugged conditions aboard a sailing vessel, Harrison’s device offered unparalleled accuracy on long voyages and a solution to the problem. Unfortunately, Harrison battled for the remainder of his life to claim the prize offered by the British government for creating such a timepiece.

Of course, modern timepieces have advanced rapidly. The next ‘great’ advancement was the wristwatch, or more specifically, the digital wristwatch. Quartz crystal displays the useful property of piezoelectricity. When placed within an electric field (attached to a power source) the crystal will change shape. By sculpting the crystal’s shape into that of a tuning fork, it can be made to resonate at a specific frequency, which in turn, allows for these cycles to keep track of time. In effect, the regularity of the quartz bending and flexing (through electric stimulation) can be specified by shaping the material in a specific way and can be electronically ‘tallied’ and modulated to the base unit of seconds (and, in turn, minutes, hours etc). Even further improvements to the measure of time were introduced with the atomic clock. This method of time-keeping, in a very general sense, works similarly to the oscillating quartz crystal, however the crystal is replaced with radiation. Most commonly, caesium gas is used as the oscillator, and excited by beaming microwaves into the apparatus. The universal ‘second’ is thus defined as the number of cycles of radiation emitted by a caesium atom when progressing through two levels of the ground energy state. Basically, the point I am trying to illustrate here is that the measurement of time becomes increasingly accurate as the underlying complexity increases. The concept of a ‘second’ has improved from a simple definition (time taken to fill a holding capsule – water clocks) to one involving cycles of radiation as an atom is excited (9 192 631 770 cycles : 1 second). Therefore, with an increase in the inherent complexity of the underlying measurement unit (the second) and the regularity of the cyclic period, we see a direct relationship to overall accuracy of both the device and practical applications that make use of time.

But what does it all mean? What is the point of pushing the development of timepieces towards increasing accuracy? As in Harrison’s time, navigation relies heavily on the use of accurate time keeping. GPS works by establishing communication between orbiting satellites (at least 3) and the ground receiver unit. A timestamped signal and orbital information are transmitted from each satellite (an atomic clock is installed on each orbiter) to the ground. The receiver calculates the delay between transmission and interception, then uses the process of trilateration to determine the object’s ground position on a sphere (centred around the satellite). By combining three of more satellite sphere, the exact location can be pinpointed (at the intersection of each sphere).

Thanks for reading my brief introduction to the history of time measurement. The next part of this article will explore more philosophy-orientated subject matter, and use the knowledge of how we measure time to discuss how we think about time and place ourselves within its boundaries.