What does 'Motion-based' mean? Well, let’s list a few examples below:
- A day is one rotation of the earth.
- An SI second (the new standard for measuring seconds) is based on the decay of a Cesium atom – that decay is expressed as regular pulsations.
- A year is a standard orbit of Earth around the Sun.
- A month is a standard orbit of the Moon around the Earth.
- A light year is the time it takes a photon of light to travel from one point in space to another.
- We travel at roughly 70 miles per hour on the highway on our way to work (e.g. the velocity expressed equals time to cover a distance in continuous motion).
- Time flies when you’re having fun. I’ve added this here because there is an important perception consideration for time that appears at least to be related intensity of activities (this as we will see is also motion-related although at first it doesn't seem to be intuitively).
- The Galactic Year is the time it takes the solar system to orbit around the center of the Milky Way (estimated to be 250 million years or so).
- Geocentric Coordinate Time (also known as TCG) - This is defined as “a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth: that is, a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. It is therefore not influenced by the gravitational time dilation caused by the Earth.” We will list all formally defined "Time Measurement Systems" 2 posts from now.
Now this last example I included is particularly interesting because it is an international standard already being used to help assign coordinates in 4 dimensional spacetime – it was defined specifically to conform to current theory relating to relativistic space. However, as one can tell from reading the description, it is largely limited to the study of coordinates within our solar system. Another interesting fact is that it is only one of several competing coordinate time systems that have arisen to help astronomers deal with the same Use Case we described in our first post on Time – the ability to locate events within spacetime.
One of the main problems with all of the coordinate systems and even with our current theories on spacetime is the earth-centric perspective we tend to toss in. What does that mean? Well, for the above example we are taking into account planetary motion but not the overall motion of the solar system, the galaxy etc. We touched upon the “taxonomy” of motion context in an earlier post and here it is again (and it actually extends to much lower measurements):
- The earth rotates – motion vector 0
- The earth orbits the sun - motion vector 1
- The solar system travels within its neighborhood in the milky way - motion vector 2
- The milky way itself is rotating – motion vector 3
- The milky way is also hurtling towards the Andromeda galaxy and will collide with in about 25 galaxy years - motion vector 4
- The universe itself is expanding outward at incredible speeds. In fact according to the latest data it is speeding up and some of it even appears to be moving away from us faster than light (1.4 C)!
So, each of these motion contexts listed above has its own velocity, trajectory and mass/gravitational considerations.
|There's a whole lot of motion going on around us, do we continue to ignore it?|
This taxonomy doesn't include any of the motion that might be occurring on the surface of the planet. That could include walking, riding in a plane, the motion occurring beneath us in Tectonic Plates or even the earth’s core (which is what generates our magnetosphere) or the motion with our bodies or even at the sub-atomic level. There is motion everywhere it is exists at every scale imaginable. More than that though, all of this ‘Contextual Motion’ is occurring along different trajectories. So let’s talk about this in relation to a coordinate system for finding an event in spacetime. The current coordinate systems use four vectors (3 for 3 D space 1 for time t) to locate planetary bodies in space. A scientist might ask the question, where will Saturn’s moon Titan be in ten years on January 10th, 2:00 pm eastern time? Using this type of coordinate system and extrapolating the known orbital behavior of Saturn around the Sun and Titan around Saturn we can plot where it will be at the designated time and date from the perspective of Earth. This works to some degree of precision for the following reasons:
- It’s still very close to us (from both the galactic and universal perspectives).
- We are deliberating pegging it to Earth time so using standards based on Earth motion is ok.
- We assume all other contextual motion will continue moving along the same trajectories they have been so we don't ever bother to factor them in – they become a more or less “absolute” background. The only motion we concern ourselves with is within our own Solar system.
So, if we try to extend this out to a galactic scale we see where the problems will arise almost immediately:
- We’re dealing with massive distances.
- We can’t or shouldn't use Earth focused time scales for managing coordinates.
- Contextual motion becomes very important once we move away from a localized perspective. We can no longer view external motion as an absolute because it in reality it isn't. At the galactic scale it becomes dynamic (and in fact always was even at our scale although that dynamism isn't regularly perceptible by us).
The problem becomes more immediately noticeable if we decide we need to locate more discrete events – e.g. something smaller than a moon’s orbit – something let’s say like locating the “Peach Orchard” action that occurred on the second day of the Battle Gettysburg (see figure below). This particular event also has the distinction of having occurred in the past rather than the present or future. The diagram illustrates rough Geo-spatial coordinates and major arcs of movement but without topology (altitude) . It wouldn't be too much of a stretch to add topology and clock readings (taken by observers of the battle) next to the movements in the diagram although we cannot be sure how precise that the clock readings are. The real question we need to ask ourselves is this; would the 4-vector coordinates for this reference frame and set of events (the location in Gettysburg and the time the action started and when it finished) be sufficient to actually locate the timespace where the battle occurred?
|We know where it occurred and when it occurred, but would this be enough to find the actual event?|
You might be asking yourselves why folks in the scientific community haven’t been viewing these issues in this manner; here why:
- For most of the past century we were still assimilating and validating the core premises of relativity and quantum mechanics – it was a lot to digest. We've also become obsessed as to why those three theories don't match up rather than challenging the underlying premises of all 3. The theories have become "institutionalized" - we experienced 30 years or so of radical conceptual expansion which ended in the 1930's (for the core theories) and then settled in around those core theories rather than taking them to the next level.
- It’s only recently that we've begun looking further into space and decided to look for tiny objects like planets.
- It’s hard for people residing on Earth not to view the Universe from Earth’s perspective – and it wasn't that long ago that most people thought that Earth was the center of the Universe.
- It’s a lot easier to make math work if 1 – the formulas are simpler, and 2 there is a fixed reference point to compare to. And science currently rewards the least complicated theories and formulas. The problem with that of course is that some aspects of nature are complicated.
This last point is particularly interesting. For those of you who have read anything about Special Relativity you will probably recall thought experiments such as at the observers on the train platform watching the lightning bolt hit from different perspectives. We tend to construct of all these scenarios as 2 observers in relative motion to one another or to an observer stationary in relation to another. The thing is when we construct it that way we leave out all of the potential contextual motion that may be occurring (or complex event scenarios). Perhaps the limited set of variables is OK to determine whether time dilation or other relativistic phenomenon is occurring or not, but is it sufficient to predict truly accurate event coordinates? Maybe not...
We will explore that and Relativity, Quantum Mechanics and Mach's Principle in our next post. The thing is - in order to understand Time - we have to tackle almost all of Modern Physics.
copyright 2013, Stephen Lahanas