Placeholder Image

字幕列表 影片播放

  • This is probably one of the most difficult questions you can ever ask a physicist or

  • philosopher... I am not a physicist - yet - nor a philosopher, but here I am, little

  • old me, not only wondering about the nature of time, but also making a first ever Youtube

  • video about it. My aim is to make you think, to create discussion... And of course, I hope

  • you enjoy the video!

  • The answer to what time is may be as simple as "Time is what the ticks of a clock measure"

  • or "Time is what keeps everything from happening all at once". But let's dig a little bit deeper

  • and make this video a bit more fun!

  • Let's start with Newtonian time. Newton's view of reality implied that time was external

  • and absolute. Newton's time is a kind of container, where events take place in a completely deterministic

  • way, linearly and independently of the observer.

  • Then came Einstein. His theory of special relativity, and then general relativity, both

  • led to the conclusion that time is relative to the observer. Time depends on where you

  • are and how you move relative to others. There is no such thing as universal time. Space

  • and time are constrained by c (the velocity of light) in such a way that the "now" of

  • one observer is not the same as the "now" of another observer. Mass, equally, can also

  • distort space and time.

  • Time dilation and length contraction are not just theoretical constructs within an elegant

  • theory. These effects have been tested again and again without failure; at macroscopic

  • scales, Einstein's theory has been shown to be a very good model of reality.

  • Let's talk about time dilation with an example. We have the elementary particles called muons,

  • which have a half-life of around 1.5 microseconds. That means that if we have, say, 100 muons

  • in the lab, after 1.5 microsecond has elapsed, we will have, on average, 50 muons left. The

  • other 50 will have disintegrated. After another 1.5 microsecond, we will have, on average,

  • 25 muons left... And so on.

  • These particles are produced at the edge of our atmosphere due to incoming cosmic rays

  • hitting air molecules. They are constantly produced so there is a constant fall of muons

  • towards the Earth's surface, travelling at nearly the speed of light. What is observed

  • experimentally is that more muons are detected than one would have expected, when we consider

  • their average lifetime.

  • This fact can only be accounted for when we use the model of time and space given by Einstein's

  • special relativity theory, where time and space are constrained by c, the velocity of

  • light, and so times and positions are relative to the observer. In this case, from our point

  • of view, the muon's own time appears dilated. More of them can reach the earth's surface,

  • from our perspective, because a second of their time lasts longer than a second of our

  • time.

  • So we can see that from the very beginning of last century, the concept of absolute time

  • was shattered, and time was understood as being completely dependent on the observer.

  • Newton's absolute time is only a good approximation, when speeds are low and when we can effectively

  • neglect the effects of nearby masses.

  • Now, let's take a look at the concept of time from a philosophical point of view. We have

  • what is called the A theory of time and the B theory of time. These were introduced by

  • the philosopher John McTaggart at the beginning of last century as well.

  • The A theory of time says that the only "real" time is the present; the past is gone and

  • the future exists as just a probability distribution, a potentiality of possible things that can

  • happen. There is no set future - on a kind of imaginary line "laid out there" for us

  • - just waiting to happen. Therefore, the future is not "real".

  • On the other hand, the B theory of time says that past, present and future all co-exist,

  • and are as "real" as each other. The B theory says that the distinction between past, present

  • and future are just an illusion of consciousness.

  • One of the consequences drawn by many orthodox physicists as a result of either Newtonian

  • physics or relativity theory is that determinism is a fact. That the past completely determines

  • the future, and hence, all what has happened since, say, the big bang, was determined by

  • the initial conditions, including you and me and our actions, thoughts and feelings.

  • There is no room for free will, which is seen as just an illusion, when we take this deterministic

  • point of view.

  • Hence, it seems that it is the B theory of time, not A, the model of time that most closely

  • agrees with the classical equations of physics.

  • So... It appears that common sense agrees with A Theory, but classical physics agrees

  • with B Theory. Could it be that time is a bit more complicated than what A or B theories

  • of time suggest? That reality is a mixture of the two ideas? Could it be that a linear

  • model of time is not a good approximation of reality? We will explore this issue in

  • a bit when we talk about Quantum Physics.

  • Now - before going into quantum physics - let's take a little break. How do I personally think

  • of time? What is my own experience of time?

  • On a personal level, I intuitively feel that time is not some mysterious external dimension

  • or construct that flows in the forward direction, that kind of dictates in what order events

  • can happen, but I feel that it is rather a much much more fundamental concept, even more

  • so than space.

  • I see time as a concept that is intricately linked to the individual's perception of change.

  • I think of time as "the perception of duration, of change and the ordering of events" by a

  • living entity or, in fact, you could say, by a conscious entity (here I'm defining consciousness

  • in line with awareness, hence animals and primitive organisms would have their own concept

  • of time, depending on how they perceive change).

  • On the other hand, I do not see time as a strict illusion either, nor as a block of

  • events completely determined beforehand. I see it as a pliable tool which, when used

  • within this particular universe, it enables our experience of 3D space and the perception

  • of the ordering of events.

  • In this way, I often ask myself that, if time can be thought of as the perception of change...

  • what happens when there is no change and no perception? Imagine you are somehow still

  • conscious, but confined in a universe where nothing ever happens and you have no perception

  • of any change whatsoever occurring (this reality would obviously be nothing like our physical

  • universe).

  • What are you left with? The first thing that comes to mind is that time does not make sense

  • in such a universe, it does not exist, unless change can be perceived by some sort of being

  • or beings that populate it so that some order can be assigned as to what goes first, what

  • goes after, etc. Maybe time could be thought of as a perpetual "now" under those conditions.

  • And all these thoughts obviously bring up the idea of universal versus relative or,

  • we could say, individual time. However, here we are talking of ideas beyond Einstein's

  • relativity theory. We are not talking about time and space in our physical universe obeying

  • certain rules, whereby c, the velocity of light, and mass, restrict how space-time behaves...

  • but in addition to this, we are talking about time being something that is meaningless in

  • the absence of an entity / a being (or a consciousness, an awareness) who is able to perceive change,

  • therefore being able to assign a "before" and an "after" to events that occur.

  • The other idea that I often wonder about, and that I feel is very important too is:

  • are space and time fundamental? If so, are they equally fundamental? Could it be that

  • one is more fundamental than the other?

  • I intuitively see time as more fundamental than space. I can sort of picture a reality,

  • a state (let's say a state outside of this universe) where space does not exist but time

  • does, where only patterns of "states" exist and there is a chronological order that can

  • be perceived between them (this is analogous to, say, my thought space, when I meditate

  • for instance... and I reach certain states, where there is no feeling or perception of

  • space, but there is definitely a perception or distinction between different states and

  • a perception of which one preceded which).

  • So time can be thought of as a fundamental structure that allows perception of order

  • between changing states or patterns (that is, order as in before and after).

  • A property can then be added so that there isn't just order between states, but there

  • is also a rule that regulates the basic fundamental tick between events, beyond which change can

  • not be perceived. In our physical universe, this fundamental duration could be the Planck

  • time. I will expand on the concept of the Planck units in other videos.

  • On the other hand, I cannot imagine the perception of a 3D physical space, existing independently,

  • without time. The way we perceive physical space is dependent on the time it takes for

  • light to reach our eyes. Even if we talk about non-visual perception, all other types of

  • physical senses are constrained by the velocity at which information within space can be transferred

  • physically to our senses. So any successful perception of 3D physical space is tied to

  • the existence of time.

  • This is of course, my own interpretation of time. But what does current science have to

  • say about this? Well, recent research carried out by a particular quantum gravity research

  • team, involving quantum universe simulations, seem to indicate that time is fundamental

  • (not emergent), that it existed before space, and not only that, but their theory says that

  • time has no beginning nor has it got an end!

  • (For references, please see the video links at the bottom, in particular, the talks by

  • Renate Loll, a professor of theoretical physics).

  • As computer simulations get better and better with time, it will be fascinating to see what

  • kind of universes can be created and what we can learn about the nature of our reality.

  • All these concepts are inevitably linked to the debate of whether the world exists out

  • there, independently, without needing aware or conscious entities to perceive it. It seems

  • that my particular interpretation of time, as I have discussed so far, does not make

  • sense unless some sort of consciousness is involved (be it a consciousness perceiving

  • our universe from within it or from outside of it).

  • So, is there an objective reality out there when there are no conscious beings to perceive

  • it? This is a fascinating subject that quantum mechanics brought to the surface within the

  • context of science, at the beginning of last century; a subject which was by no means new

  • and which many religions and philosophers had already debated for thousands of years.

  • But the fact that this can now be studied within physics is very very exciting.

  • When it comes to consciousness, unfortunately, many physicists cringe when they hear this

  • word. However, this debate was NOT started as a kind of new-age idea, but rather, it

  • started within the context of experimental science (for example, when discussing the

  • possible interpretations of the double-slit experiment results).

  • It seems to me, that it is partly due to some new-age ideas that flourished later on, which

  • use quantum mechanics as a kind of platform to support their theories about reality, that

  • today many scientists feel uncomfortable when having to consider consciousness as having

  • a fundamental role in the way the physical universe works (let me clarify, this is independently

  • of the validity of these new-age ideas! I personally have no problem with any kind of

  • ideas, as I try not to have any prejudices or pre-conceptions). The important thing to

  • remember is that these ideas were initially brought to the surface by many of the eminent

  • scientists who were at the forefront of quantum mechanics at the time.

  • Einstein, Bohr, Schrodinger, Heisenberg, Wigner, Bohm, Wheeler... The list goes on. These are

  • not new-age quacks (a word that pseudo-skeptics seem to over use these days, in my opinion)

  • but the very brilliant minds who laid the foundations of quantum mechanics.

  • Most of these scientists didn't just shut up and calculate (a very famous quote by Feynman)

  • but they discussed the philosophical, metaphysical and physical interpretations of quantum mechanics.

  • Consciousness (or mind), the existence of objective reality, the illusion of time...

  • These were not new age ideas, but very important ideas about reality that originally came from

  • the bunch of brilliant scientists who created quantum theory.

  • I find it very unfortunate that many mainstream scientists today seem to want to distance