Friday, 5 August 2011

A Subjective View of Time

In my previous post Is Time a Dimension?, I presented a case that time is a dimension. I also pointed out that even the greatest minds in science can't agree on a single definition of time. I'm sorry to disappoint you if you thought I had discovered the holy grail of time! Like many other pundits I have my own ideas about time, however.

Let's start by thinking about how we perceive time. In our personal experience, we are aware of time passing - in one direction. We don't appear to be able to move backwards in time and seemingly can't move forwards in time (other than one day at a time). We can remember the past and we can visualise the (possible) future but we seemingly can't access it or interact with time other than in the present moment.

But what is the present moment? Can we ever hope to perceive the universe as it is NOW? The answer to that is a resounding NO! As I will now explain, time and space can cause optical illusions and time itself is different for every observer.

First, let's consider how distorted our perception of space can be due to the vastness of space and the speed of light.

The speed of light limits our ability to view the current moment

When we look out into the night sky, we are not seeing the stars as they actually are at this moment in time. The light from each celestial object has travelled to our eyes at a speed of 300,000 kilometres per second. The distance that each beam of light has travelled is so great that by the time it reaches our eyes, it may have been travelling for years, even centuries or more. We are seeing the light it emitted at a point in time equal to its distance from us divided by the speed of light. Because the stars are at different distances from the Earth, we are therefore looking at a time-distorted snapshot of the universe.

Light from the Moon takes just over a second to reach us and from the Sun, about 8 minutes and 19 seconds. The nearest star, Alpha Centauri is so far away that its light takes 4.27 years to reach us. We express cosmological distances in those terms, so we would say that Alpha Centauri is 4.27 light years away from the Earth. The furthest object ever observed to date is over 13 billion light years away! (However that can't be seen with the naked eye.)

Here's an interesting video by Carl Sagan from 1980 where he demonstrates how our view of the cosmos is not only distorted but changes through time due to the relative motion of the stars.

Travels In Space and Time

So, what we see in the sky is distorted because we are looking back a different length in time for every visible object. That may be reasonably easy to understand but there's an aspect to time that's a lot less easy to get your head around and that's the time dilation effect of special relativity.

There's no such thing as a universal "Now"

Probably one of the greatest scientific achievements of the 20th century was Einstein's theory of relativity. According to this theory, we can change our own unique time frame relative to one another, depending on our relative speed and the differing effects of gravity. This is called the time dilation effect. The theory states that the rate that your personal time frame elapses depends on the speed you are travelling and the amount of gravitational force you are subjected to. I'll let the following video explain this.

Time Travel: Einstein's big idea
(Theory of Relativity)

The faster you are travelling and the greater the gravitational pull you are experiencing, relative to someone observing you, the slower your time frame elapses relative to them. It's not just you that appears to slow down, but everything in your time frame: your own personal universe, if you like. You witness your own world elapsing at the "normal" rate, but someone observing you from a different relative speed or subject to a different amount of gravitational pull would see you moving more slowly Eventually you would appear to freeze in time as you approached the speed of light or when you were in a massive gravitational field such as at the event horizon of a black hole.

The time dilation effect has been proved to be correct in practice. As Renate Loll said in my last post, "satnav" satellites gain 45 billionths of a second a day due to their lower relative gravity. If the positioning calculations ignored this effect, then after a week your reported position would be 10 kilometers in error!

Most sources that describe time dilation patronise the reader by saying that its effects are only significant when the relative speed between observer and observed is a significant fraction of the speed of light. That may be enough to satisfy most practical situations, but what about the philosophical implications?

If you went on a long journey in a hyper-speed space craft, you might return to Earth years later to find that you had only aged a few years whereas I would now appear decades older than when you last saw me. Clearly you have moved into a different reality relative to the one you would have experienced had you stayed at home.

If you accept that argument then you should be able to see that if your time frame elapses only one Planck unit of time different to mine then the same principle applies. If you have moved in time at all at a different rate to me then when we meet again, we are no longer sharing the same reality as we did when our time frames were synchronous.

A Planck unit of time is about 5.4 x 10-44 of a second. I have calculated that if you walk away from me at a speed of one metre per second for only one second then you will have changed your time frame relative to me by more than 1026 Planck units by virtue of the time dilation effect! In my last post I offered one description of the present moment as consisting of a succession of "now-points": slices of 3-D reality at the Planck scale.

Now consider what this implies about the nature of of our perceived reality.

Every object that is in motion relative to other objects and every object that is subjected to a relatively differing gravitational pull is in its own time frame: its own reality.

So the idea of "now" is subjective for every observer. We all exist in our own unique reality. That's a stunning conclusion from a relatively simple mathematical equation!

So, when you look out into the night sky, even if you could see the stars in "real" time without time and distance distorting the picture due to the speed of light, you would only be viewing the heavens in a time frame that was real to you. Each planet, star and galaxy would be experiencing time elapsing at a different rate to your time.

We choose how time unfolds

Our subjective experience of time depends on the choices we make in terms of our speed of movement and location with a gravitational field.

At any particular now-point there is theoretically an infinite number of possibilities of what the next succeeding now-point might be from which we use our free will to make a choice. The vast majority of those possibilities would be unlikely to manifest themselves into your current reality because the historical series of now-points that led you to the current one make some options more likely than others.

Read that again if you don't quite get what I'm trying to say then consider this example.

So let's say you've graduated from university with a first class degree in mathematics. What will happen next? Will you take up a career in academia? Will you go into industry? Will you drop it all and become a musician instead; or will you decide to drop out and become a street bum begging money from passers-by? Each of these possible futures are possibilities but you can guess that the first two are more likely futures than the latter, given the path that you have taken so far. Which ever future you choose to aim for, the future that you will actually realise is influenced by the choices you are making in the current now-point.

OK, I understand that your future career isn't going to manifest itself in the next Planck frame of time! However, the unfolding of any particular version of your future is more (or less) likely depending on what the next now-point is and, having made that choice, the ongoing probabilities change on the basis of that choice, steering you ultimately in the direction of your intention.

In summary, the future consists of what mathematicians would call a probability space of possible futures and the one you experience is a result of your choices and the choices of those who affect you. This begs some important questions:

Q. What happens to the unrealised futures? Do they exist in any real sense?

You may be amazed to learn that theoretically the answer to this is "Yes"! In my post 10 spacial dimensions: what does that mean?, I left the door open to parallel 3-D worlds and I'll return to this subject in a later post.

I've reached a point where I want to stop discussing time and move on. However, there are numerous other questions that we could address at this stage. Here are jut a few.

Q. Does the past "exist" in any real sense? Q. If we don't have the ability to remember the past, would we be able to perceive time elapsing? Q. Do unchosen, unrealised futures not exist just because we are not currently witnessing them? Q. Could time actually be a human construct, imagined inside our minds?

In my next post I will introduce a dose of quantum weirdness by discussing the role of the observer in creating reality by describing the famous "double slit experiment".

From the perspective of THIS universe, I am "The REAL" Jeff Hall

More reading

Another video on Time dilation:
Time Dilation - Einstein's Relativity

For the mathematically minded reader there is a good source of information on time dilation and relativity on wikipedia: The Time Dilation Effect.