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?
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15 May, 2008 at 1:57 pm
Dennis Quine
V:
The “Principle of Local Action” arises, as you correctly assert, out of the “universe’s speed limit” of light velocity: 300,000 kps minus some change. As first stated by Einstein, the idea was novel because Newtonian mechanics assumes an infinite speed for light, so that something called “universal time” is possible. In the concept of universal time as proposed by Newton, there is a “now” that applies to everything and everywhere at the “same” time. Effects are assumed to propagate instantaneously over large distances.
In Newton’s time, no one had a clue as to how fast light actually travelled, and the assumption of “infinity” was acceptable. When it is realized that light has a finite velocity, then the next step was to realize that information and physical effects must be propagated at finite velocity also. So “now” (simultaneity in technical language) referred to points connected at light velocity. We can imagine things occuring outside the light cone (e.g., the sun going nova), but information about the event (and its effect of frying the earth) must wait for that old slowpoke: light.
For most of the things in our life, “now’ still seems to be universal and instantaneous everywere because light is so fast compared with everyday events. However, when we have delays in conversations from around the globe caused by the bounce of the telephone or TV signal to geosynchronous orbit and down, then we get a slight taste of the fact that time is not a uniform, universal medium the same everywhere. “Now” here, and “now” half a planet away are determined by the propagation of light between the two points (and delays in bouncing off satellites).
The apparent propagation of entangled quantum effects “instantaneously” between remote locations raises the possibility that on some level in the universe there is indeed a Newtonian “universal time”, the same everywhere, and that simultaniety is not constrained by light velocity on that submicroscopic level.
An alternative explanation of the apparent infinite velocity of propagation for collapsing entangled states is that time as we experience it does not apply for subatomic events. There is some reason to believe that the “flow of time” that we experience is a macroscale effect observable only for more complex aggregated structures like molecules and larger, and does not even exist at the level of subatomic particles. They may exist in a timeless state, so the concept of propagation of effects at “infinite velocity” just doesn’t apply. But all we have are the indicators of high energy particle experiments, a gross instrument for probing such sensitive effects.
A question I find intriguing is why light has the speed in vacuum that we observe. Why 300,000 kps and not, say, 500,000 kps? We can slow it down (just run it through water or glass), but cannot speed it up. The speed of light in vacuum is the upper speed limit, apparently fixed at the time of the big bang.
But it is an independent fact of life, something like Euclid’s postulates for plane geometry. It cannot be derived from the other facts we have about the constants of the universe. So why not twice as fast (or 1/2 as fast)? The value of c enters into a lot of the basic equations of physics, but its actual value (300,000 kps) is a contingent, not a necessary number. If c were determined to be 500,000 kps, nothing would change. So why is it fixed where it is?
One of many remaining mysteries about the universe.
Happy Theory of Everything Day,
DHQ
17 May, 2008 at 8:48 am
vulcanis
It is intriguing to think that time is dependent upon space, in the sense that on a subatomic scale time seems to cease existence. It is a very hard concept to get one’s head around. Imagine a timeless state whereby the notion of travelling between two points is instantaneous. It would be an incredible experience; existing throughout all points in space at once. Perhaps the most intriguing part of such a concept is that our existence is actually made up of individual timeless particles. Every quark and gluon that makes up our bodies is existing in such a timeless state; collectively time seems to emerge from timelessness. Perhaps this is telling us more about the Universe than we think; how the concept of time emerged in the Universe following the Big Bang.
Thinking about time and locality in this way seems to help in gaining insight into string theory. The main posit of this theory is that on a sub-atomic scale, 8 or so dimensions (depending upon which flavour of string theory one subscribes to) are so tightly curled up that they are only directly experienced on a microscopic scale. Therefore it is possible that such super-tiny dimensions, when traversed by such tiny particles, allow for seemingly instantaneous travel.
17 May, 2008 at 2:27 pm
DENNIS QUINE
V:
The universe does seem to be much more intricate and compicated than we have imagined. Our “common sense” about things is formed from very early experience: dropped objects fall to earth, light travels at an infinite speed, it hurts to touch hot objects, and so on. Studies of high school kids’ beliefs about how the world works have shown almost total ignorance of basic physics, forget modern physics, even after 8 years of “science” classes. They seem to have an intuition about things that is pre-newtonian: when confronted with newton’s laws initially think they are incorrect, don’t match experience.
So its not surprising that we have to spend a lot of time trying to forget what we “know” when confronted with actual experiments regarding the world. P.W. Bridgeman (Nobel, Physics 1948) once wrote that new ideas (he was speaking of relativity) are not so much adopted by the current generation of physicists, but that the older ones just die off and the new generation grows up with the ideas and finds them “intuitively obvious”. How much harder for us on the sidelines just watching the development of theory and experiment to make sense of things.
I wonder if humans did not have memory, if the concept of time would ever even have been created(?) And, living on a time-constrained level of the world, whether we have interpreted the experiments from a time-independent level (sub atomic) correctly. All lwe have there are after-the-fact entrail readings of what particle detectors say happened. I thought “science” was supposed to simpify the world and make it more easily understood. Seems the more we know the less we understand.
Living in the state of “Confusion”,
DHQ
28 May, 2008 at 5:33 pm
harmoniously
harmoniously says : I absolutely agree with this !