“What is time?” That is a question that has been pondered and debated for probably thousands of years by some of the finest philosophical and scientific minds ever produced, without any definitive resolution. So, I’m NOT going to pretend that this is THE ANSWER – the be all and end all to the question. It’s some of my thoughts, which hopefully are as valid as anyone else’s!
What Is Time? It has been said that time is just Nature’s way of preventing everything from happening at once! But the word ‘happening’ is significant because if something happens, something changes. To my way of thinking, time is synonymous with change; time is a measurement of change; change gives the concept of time tangible meaning. If nothing ever changed, if nothing ever happened, it would be meaningless to talk about time. Time is just our informal perception or more formal measurement of rate-of-change. Rates-of-change vary depending on how fast you travel relative to some other frame of reference (the General Theory of Relativity) so the time intervals that measure that rate-of-change vary accordingly. I also can’t help but wonder whether, speaking of things relative, whether one could insist on a constant rate-of-change that’s made constant because your rate-of-time varies, or the more common view from day-to-day experience that rate-of-time is constant but rate-of-change varies.
It’s not difficult to understand why you are not aware of time passing when you sleep. It’s because you’re not aware or cognoscente of anything changing while you’re asleep. In fact, sleep is a way of achieving time travel. You go to sleep at 11 pm. Next thing you know its 7 am and you’ve traveled eight hours into the future seemingly instantly!
Thusly, I conclude that time doesn’t have a separate reality. I mean you can’t weigh time, it has no mass, it has no charge or energy, it isn’t a force and has no particle associated with it, you can’t put time to any physical use, nor can you manipulate time. You certainly can’t bottle and sell it! It’s about as intangible a something as the Universe allows.
Did time exist before there was anyone around to put a label to it? I mean in a pre-life era, change certainly took place – rocks eroded, the tides ebbed and flowed. But was there time? I suggest the answer is ‘no’ in that it takes a certain level of intellect to recognize change or rate-of-change. A rock doesn’t perceive time, nor does the beach upon which the tides act. The changes are physically real enough, but it takes something as complex as a living organism (not of necessity just a human organism) to perceive and understand change, and rate-of-change, which – human beings – for lack of a better word, we call it all happening (i.e. rate-of-change) as a concept called ‘time’.
By analogy, there is the oft quoted puzzle of there being this tree in a forest which falls. Does the falling/fallen tree produce any sound if no one (meaning humans) is around to hear it? (Of course there would be animals like bears, deer, possums, birds, etc. that would hear the sound, but let’s suppose that the forest contains just plants which I assume we can agree on, can’t hear. Now regardless of whether any animals are around or not, the falling tree will produce vibrations in the air (usually air, but vibrations can be equally transmitted in a liquid or solid medium). But vibrating air isn’t by itself sound. Sound is the perception (and possible interpretation) of those vibrations, and that takes a detection device and software (ears and a brain). So, there is no sound without ears and a brain, although the vibrating air is quite real regardless.
Time too, by way of my analogy, is akin to sound; change or rate-of-change is akin to the vibrating air. The former two (time and sound) are perceptions of physical events; the latter two (change and vibrating air) are the real physical events.
You’d think that therefore time wouldn’t exist in a vacuum or at a temperature of absolute zero, as how could anything change in a vacuum which contains nothing or at absolute zero when all motion ceases? Ah, enter the weird and wonderful world of quantum physics and discover that quantum activity, happenings, change, motion, etc. exists even in an apparent perfect vacuum and even at as close to absolute zero as makes no odds. In quantum physics, there’s no possibility of a perfect vacuum; absolute zero is only abstract and can’t ever be actually achieved. Therefore, time always exists as well. There seems to be no way to ever shut down quantum activity and achieving a perfect vacuum and/or absolute zero, so we’re in no danger of ever having our perception of time cease.
The shortest (quantum) unit of time possible is just that interval below which no possible change can happen. In other words, even the quickest ever possible change one can imagine takes an absolute minimum amount of time.
Change also implies there must be causality – there must be a cause that produces an effect, or in other words, something is affected by something else that occurred previously. Going from cause to effect implies a change and a time interval must have taken place into which that change fits. This introduces the commonly used phrase ‘arrow of time’. If time is our perception of change, then what is the ‘arrow of time’? Methinks it’s the reality that on the macro scale at least change happens only in one direction – cause precedes effect; effect follows cause, and that’s change. Examples of such one way cause and effect change include dropping the china cup and it breaks. A broken cup does assemble itself and then leap off the floor into your hand. Humans tend to be conceived, get born, grow up and age. Hair turns gray (or falls out), you get wrinkles and liver spots, and you die. You don’t rise from the grave, re-animate, and age backwards towards childhood and pop back into the womb! A hot cup of coffee cools off to room temperature. A cold cup of coffee doesn’t heat up by itself; even if there’s potential energy enough in the environment (air molecules flying around) to theoretically heat it up. In other words, you can’t unscramble (or un-boil) an egg.
Present Time: The Concept of ‘Now’: Does the present actually exist? We speak of it was if it does. But does it? Now I’m sure there’s no debating that there is a past, and that there will be a future. I’m sure there’s no debating that what we’d call five years ago exists in the past; five years on from when you read this is clearly the future. What about five months ago, or ahead? What about five days or five hours or five seconds? Is half a second ago the past? Is half a second hence the future? Of course it is. In fact, I suggest you can split units of time ever shorter and shorter, but still admit that ‘ago’ means past; hence means future, even if 0.000005 of a second ago really is past, and 0.000005 of a second hence is the future. So where comes the ‘now’ or the present?
While there is a past, and will be a future, there really does exist a present. There apparently is such a thing as the shortest interval of time and nothing shorter can exist in reality. That shortest interval of time is known as Planck-Wheeler time, below which time as we know it ceases to exist. It’s about 10 to the minus 43rd of a second. That’s how long your present lasts for! One Planck-Wheeler time unit behind you is now forever locked in as part of your unalterable past. One Planck-Wheeler time unit ahead, is still part of your malleable (free will?) future.
Even without resorting to quite such a tiny present, physics logic suggests that you really are an isolated individual that cannot share the present with the rest of the world. Lets imagine this couple, say we call them Clive and Jane, sitting down for their evening meal. Clive says to Jane, “pass the salt please darling”. Now Clive utters that phrase in his present and Jane hears it in her present. But both presents aren’t simultaneous. When Jane hears it in her present, it’s simultaneously Clive’s past because it takes time for sound to travel from voice to ear (and light from mouth to eye). Actually, when Jane hears the word “salt”, “pass the” is already in her past while “please darling” is still in her future. In other words, Clive and Jane can’t ever share the same present even though both pass through identical simultaneously now’s.
Here’s a form of time travel. When Jane looks in a mirror, the image she sees in her present is actually of herself from her past – an ever so slightly younger version of herself because it takes an interval of time for the light to be reflected off Jane, onto the mirror, reflected off that, and back to Jane’s eyes.
In summary, nothing you see or hear has the exact same reality that you perceive in your present because there has been a time lag and things change over time – even incredibly short intervals of time. A common example is looking at a distant star. The star you see in you’re here and now isn’t the same star that exists in that same here and now. You’re looking at a star, which, for all you know, just may no longer exist!
Of course you do live your entire life in the actual ‘now’ – you certainly don’t literally live in any part of your past, nor your future. Your life, your lifetime of ‘now’, is a string of Planck-Wheeler time units.
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