hourglass with clock behind

What is time?

Marianne Freiberger

In the latest poll of our Science fiction, science fact project you told us that you wanted to know what time is. Here is an answer, based on an interview with Paul Davies, a theoretical physicist and cosmologist at Arizona State University and Director of BEYOND: Centre for Fundamental Concepts in Science. Click here to see other articles on time and here to listen to our interview with Davies as a podcast.


What is time?

Everyone knows what time is. We can practically feel it ticking away, marching on in the same direction with horrifying regularity. Time has enslaved the Western world and become our most precious commodity. Turn it over to the physicists however, and it begins to morph, twist and even crumble away. So what is time exactly?

To many people throughout history time would have been synonymous with the rhythms of nature; the passing of the seasons and the cycles of the celestial bodies. If this idea seems naive today, it's not only because modern clocks are infinitely more accurate time keepers than the celestial bodies ever were. It's also because we've come to think of time as something universal, something that would keep marching on even if all clocks, celestial or man-made, were to stop. The notion of an absolute time, one that's measurable and the same for all observers, was expressed most succinctly by Newton: "absolute, true and mathematical time, of itself, and from its own nature, flows equably without relation to anything external."

Einstein's time

Newton's absolute time may feel like an accurate description of the beast that rules our daily lives, but in science the notion was shattered in 1905 by Einstein's special theory of relativity. "Einstein showed that there isn't a universal time," explains Davies. "Your time and my time get out of step with each other if we move differently." In other words, the duration of time between two events can vary depending on how fast you are moving in the period between the events.

a diagram of the mirrors

Imagine two observers, one on a train and one stationary. The traveller sends a pulse of light from a torch vertically up. The traveller's view is shown on the left: the pulse travels vertically up. The stationary observer's view is shown on the right: the position of the torch and train ceiling at the start and end of the pulse's journey are shown in black and blue respectively. The pulse travels diagonally.

At the root of this strange time warping effect lies Einstein's postulate that the speed of light should be the same for all observers, no matter how fast they are moving. Imagine two observers, one travelling on a train and the other stationary by the side of the tracks. As the two pass each other the traveller emits a pulse of light from a torch shining vertically up. The two observers will disagree on the distance the pulse has travelled when it hits the ceiling of the train, because the stationary observer perceives not just the vertical motion of the pulse, but also the horizontal motion of the train.

Since both observers measure the same speed of light, and since speed is distance per time, this implies that they must also disagree on the time it took the pulse to travel that distance. Time is relative to the observer, or as the physicist Kip Thorne prefers to put it, time is "personal". (For a more detailed description, read the Plus article What's so special about special relativity?.)

We don't notice this time dilation in daily life, but it's not so small as to be unmeasurable. "If I fly from Phoenix to London and back again, and then compare my clock with that left in the office, they will be out of step with each other by a few billionths of a second," says Davies. That's a tiny amount for humans, but it's well within the measuring capability of modern clocks.

In fact, time dilation has a real impact on the global positioning system (GPS), which many of us have come to rely on for navigating around the world. "The system works with orbiting satellites that are moving very fast," explains Davies. "If you didn't factor in this time distorting effect of motion, then your GPS would very quickly begin to accumulate errors so that in an hour or two you'd be lost. So this is a real effect, not just some sort of mad mathematician's nightmare."


An artist's impression of the Sun warping spacetime and the Cassini space probe testing relativity by measuring how signals are delayed by the warping. Image courtesy NASA.

But motion isn't the only thing that can distort time. In his general theory of relativity, published in 1916, Einstein showed that gravity too can slow time. Rather than thinking of gravity as an invisible force that wafts across the ether, Einstein thought of it as the effect of massive bodies distorting the very fabric of space. A famous analogy is that of a bowling ball sitting on a trampoline, which creates a dip that a nearby marble will roll into. According to general relativity, massive objects like stars and planets warp space in a similar way, and thus "attract" other bodies that pass nearby. However, Einstein realised that time and space are inextricably linked in what he called spacetime, so the warping effect of gravity does not just effect space, but also time.

"Gravity slows time, so that it runs a little bit slower in the basement of your house than it does on the roof," says Davies. "It's a tiny effect, but it can be measured, even on distances that are that small. But if you want a seriously big time warp from gravity, you have to go where there's a very big gravitational field. If you had a clock on the surface of a neutron star, for example, it would tick at about 70% of the rate of a clock on Earth. The ultimate time warp is at the surface of a black hole, where in a sense time stands still relative to our time. If you went there, you wouldn't notice anything peculiar about time, but if you compared clocks between the two locations, they'd be enormously out of step."

Einstein drew an interesting conclusion from his results about the nature of time. In a letter to the family of a recently deceased friend, Michele Besso, Einstein wrote, "... for us physicists believe the separation between past, present, and future is only an illusion, although a convincing one." Since time is relative to the observer, it is impossible to divide it up into past, present and future in a way that is universally meaningful. In some sense, past, present and future are all there at once.

"This notion is sometimes called block time, but I like to call it the timescape because it's a bit like a landscape," says Davies. "If you look at a map, the whole of the landscape is there before you, all at once. If you add time as the fourth dimension on this map, then all of time is there at once too. The fact that nothing in physics singles out a particular 'now' is a mystery."

Incidentally, there is nothing in Einstein's theory that prohibits time travel, be it into the future or into the past. But this is a can of worms we won't open here, as you can read about it in Kip Thorne's Plus article Is time travel allowed? (or read Davies' book How to build a time machine).

The arrow of time

Thinking of past and future brings us to another problem that has foxed scientists and philosophers: why time should have a direction at all. In every day life it's pretty apparent that it does. If you look at a movie that's being played backwards, you know it immediately because most things have a distinct time direction attached to them: an arrow of time. For example, eggs can easily turn into omlettes but not the other way around, and milk and coffee mix in your cup but never separate out again.

Listen to the interview with Davies in our podcast!

The most dramatic example is the history of the entire Universe, which, as scientists believe, started with the Big Bang around thirteen billion years ago and has been continually expanding ever since. When we look at that history, which includes our own, it's pretty clear which way the arrow of time is pointing.

"But the mystery is that the laws of physics show no preference for forward time or backward time," says Davies. For example, if you can make an object move one way by applying a force, then, as Newton's second law of motion tells you, you can make it retrace its path by applying the same force in the opposite direction. So when you watch a movie of this process you wouldn't be able to tell if it's being played forwards or backwards, as both are equally possible.

"So the problem is how to account for the asymmetry of time in daily life when the laws that govern all the atoms that make up everything around us are symmetric in time," says Davies. Much has been made of this problem, which affects Einstein's physics just as it did Newton's classical description of the world.

Hand of cards

Order or disorder?

But the answer isn't all that difficult to find. Most processes we feel are irreversible in time are those that (for whatever reason) start out in some very special, highly ordered state — Davies uses a pack of cards as an example. When you first open up a new pack the cards will be ordered according to suit and numerical value. When you shuffle them for a while they will become disordered, so it seems that, as time passes, things will always move from order to disorder. "We might think that this is very strange because there is nothing in the act of shuffling that chooses a direction in time, yet we see a distinct arrow," says Davies.

However, there is nothing in the laws of physics that prevents the act of shuffling from producing a perfectly ordered set of cards. It's just that the ordered state is only one of a total of around 8 × 1067 possible states, so the chance that we come across it while shuffling the cards is vanishingly small. So small that it would never happen even within several lifetimes of shuffling.

So the apparent asymmetry of time is really just an asymmetry of chance. Systems of many components — like a cup full of milk and coffee particles or a bowl full of egg particles — evolve from order to disorder not because the reverse is impossible, but because it's highly unlikely. This, in a nutshell, is the second law of thermodynamics, which states that the entropy (a measure of the disorder) in a closed physical system never decreases. It's a statistical principle, rather than a fundamental law describing the behaviour of individual atoms. The apparent arrow of time emerges as a property of the macroscopic system, but it's not there in the laws that govern the individual particle interactions. As the physicist John Wheeler put it, "If you ask an atom about the arrow of time, it will laugh in your face."

This also applies to the whole Universe. "The Universe started out very smooth and expanding uniformly," says Davies. From a gravitational view point the Big Bang was a low entropy state and the Universe has been increasing its entropy ever since, hence the arrow of time. The question now is why the Universe started in the way it did. "Why our Universe went bang in such an ordered state is still a mystery," says Davies. "There is no agreed answer to that, partly because there is no agreed model of cosmology. We all think the Universe began with a Big Bang and we know it's expanding. What we don't know is if the Big Bang is the ultimate origin of time or whether there was a time before that." (Read the Plus article What happened before the Big Bang? for more on this subject.)

Time disappears

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One thing we have neglected to say so far is that Einstein's theory, which describes the macroscopic world so admirably well, doesn't work for the microscopic world. To describe the world at atomic and subatomic scales, we need to turn to quantum mechanics, a theory that's fundamentally different from Einstein's. Reconciling the two, creating a theory of quantum gravity, is the holy grail of modern physics.

When Schrödinger and Heisenberg formulated quantum mechanics in the 1920s, they ignored Einstein's work and treated time in Newton's spirit, as an absolute that is ticking away in the background. This already gives us a clue as to why the two theories might be so hard to reconcile. The status of time in quantum mechanics has also created profound problems within the theory itself and has lead to "decades of muddle and subtlety," as Davies puts it.

We won't go into this muddle here, but we'll note the conundrum that unfolds when you try to apply quantum mechanics to the Universe as a whole (a rather controversial approach not all physicists agree with). "If you try to write down a quantum mechanical description of the whole Universe, you find that the time parameter actually drops out [of the equations], it's not there at all," says Davies. Time is replaced by correlations. "For example, you might have a correlation between the size of the Universe and the value of some [physical] field. We would describe this by saying 'as the Universe evolves over time and gets bigger, so this field changes in value'. We use that language, but actually all you're talking about is a correlation [between physical quantities] and time can be removed completely."

Some people have interpreted this to say that time doesn't exist at all, but Davies disagrees. "I think time exists just as telephones do. It's a real thing and we can measure it. But it does suggest that the way it enters into our description of the world is different from other quantities we're used to."

One possibility is that time, and also space, are emergent properties of the Universe, which are not part of the bottom level of reality. "It may be that for the extreme conditions at the Big Bang a description in terms of other variables is more appropriate. When we see the world with a well-defined space and time [or spacetime as Einstein put it] this may just be some particular state of the Universe that has emerged out of the Big Bang." Davies uses a block of rubber as an example: it's got its very own physical properties, its elasticity for example, but these properties aren't there at the atomic level. They are a result of the atoms and the laws that govern them combining in one particular way. Similarly, the Universe, as it cooled down from the Big Bang, may have just happened to give rise to spacetime. Perhaps, if it had cooled down in another way, spacetime wouldn't have come up.

rubber ducks

Rubber ducks have emergent properties.

But if space and time aren't fundamental, what are the fundamental properties of the Universe? There is no theory that people agree on. "We can invent words to describe them and people have, but these things are not anything we are going to encounter in daily life. So we're just resorting to [mathematical descriptions]. But even if one day we manage to explain time and space in terms of something else, that only pushes the question to another level, because you then have to explain [the something else]."

So it seems that we're no closer to understanding what time is than Newton was — perhaps we understand it even less. But then, perhaps the job of the scientist isn't to fully explain the Universe, but merely to describe it. "You postulate a theory, usually in the form of mathematical equations, and then you test it against reality," says Davies. "If it does work, you don't argue where those equations come from. It's just your best attempt to describe the world."

Whether it's fundamental, emergent, or just a set of correlations in disguise, the fact is that something we call time manifests itself undeniably and we all know about it. As a friend of mine put it, "If you want to know what time is, just look at my face."

About this article

Paul Davies

Paul Davies

Paul Davies is a theoretical physicist and cosmologist at Arizona State University and Director of BEYOND: Centre for Fundamental Concepts in Science. He has worked in a number of different fields, including cancer research and astrobiology (Plus has interviewed him on astrobiology in the past) and has written a large number of popular science books, including About time: Einstein's unfinished revolution and How to build a time machine.

Marianne Freiberger, co-editor of Plus, interviewed Davies in July 2011.



Thanks for this post. Time as an emergent phenomenon...now I have something to think about...for the next several years! Well, at least I have plenty of time...


Very interesting articles,

I have thought a great deal about this subject, and it seems to me that rather than ask 'does time exist' or 'what is time' (which are loaded questions) - we should perhaps first ask ...
'what do we basically observe?' - and then see if the need or existence of an extra, and apparently mysterious thing e.g. time arises.

in my experience we basically observe matter and motion - and if wee look at this in great detail we can see that just matter existing moving changing and interacting 'now' so to speak can account for all that we observe and attribute to 'time'.

if you look at Einstein's 'relativity' you can see that he 'assumes' that (extra to matter and motion) time exists in at least some way, but without proving this. He then goes on to word his revelations in terms of 'time' ( time being dilated etc).

whereas i think it can be shown that everything he says can be seen as correct, but also just happening 'now' (with no existence of 'time' suggested or implied). -

Anyone can just casually say something like this, and such comments are ten a penny unless carefully backed up, so I wrote a book draft, set up a page, and made a few videos about it.

see 'A Brief History of Timelessness'

(one of the videos - http://www.youtube.com/watch?v=DpT9l7ZPmtw)

Matt Welcome, London

It is my admittedly simplistic understanding that the need or existence of time (in addition to matter and motion) has already been acknowledged. It is used in many equations. It is how we calculate speed, velocity, acceleration, and on and on. How can we explain what we observe in motion that is attributed to speed without the concept of time?


The chasing for shadows that gets called the understanding of time is looking too hard, in the wrong place. It's a semantics issue (not physics, not math, and not cosmology)

1. An Abstract. Time is change. Change is caused by energy differential. It is independent of time. Change happens anyway. Time doesn't cause change! Time measures and calibrates change - so "time" is a derived abstract (i.e a measurement and calibration system)

2. A collective term. Every particle in the universe has its own change history/future. Its own, independent and unique change stream. Time can't be a "frame by frame" universal (using the movie picture analogy) as all quantum particles operate independently. Time is NOT an absolute, nor universal. BUT we use the word time as the collective term for all the change streams. Every quantum particle changes in its own stream. This might be in a "frame by frame" manner- but the universe of frames are not linked, not synchronised. There is no universal single frame of time. Time is the aggregation of all change, all change stream or all frames (depending on your preferred analogy). Time is a collective term for all change.
3. An Illusion. The earth rotation governs our lives. And our bodies change continually as we age. These two ubiquitous, constant change streams (day and night, and our own immortality) have caused the notion of time being a "thing" (a flow, a stream, a dimension or whatever) to be deeply engrained in our phsyche. Its an illusion!

No change means no time. Its as simple as that!
For a fuller explanation, please see www.thisistime.co.uk

i have to say in advance that i humbly have not even the simplest knowledge of physics or anything relating to it.
My thought on this is still anchored on Einstein's relativity. Also, simply put, isn't physics sorta something that enables us to calculate, measure & understand "reality", even ones that are not within our capabilities/comprehension?
Maybe on a upper dimension, time is just as easy as walking from the living room to the dining


Children may understand time better than adults. Raised in a world with DVDs and videos a child is keenly aware of fast forwarding slowing and reversing a video. When time slows motion slows and faster motion is seen with faster time. Time at least superficially seems to be linked to motion. However a simple thought experiment can provide further insight. Imagine a satellite orbiting a larger mass. Imagine time slowing down for this system. We expect to see that the orbital motion will be slower. However for that to happen the force keeping the two objects together in orbit will also have to get weaker. Similiarly if we imagine a faster time we will expect a faster motion and the attractive force between the two masses will have to be stronger. So time involves both motion and forces. For further info on this line of thinking visit timephysics.com


In a couple of short essays available online at http://www.spacetime.nu I argue that time is actually a discontinuous manifestation of elastic oscillations of the fabric of the universe.
The Big Bang would presumably be the event that induced the oscillations.
This also reconciles Newtons absolute time with the relativity of Einstein as well as with simultaneity, which at the end of the day leads up to a possible explanation of timedilation.

Paradoxically, time is as real as our very lives yet it is an illusion dat doesn't even exist without us.Time is therefore a stubornly persistent illusion perceived only in our conscious mind. The fact that you can't measure the present moment because it has no duration further attests to the fact that time is just an illusion.


Time is a matter of scale. The laws and relationship between The micro and the macro that gives definition to quantum gravity is scale. The laws of physics are dependant on
scale. Time varies depending on the scale of the perspective.
The Old Man


I think of time as being experience, so if you're not experiencing, time is absent.


Ultimately, it seems to me, a fundamental aspect of the universe is real if, in principle at least, it can be measured either by comparing two quantities of it or observing its impact on a recording device. Time has always been measured indirectly through movement, be it of heavenly bodies, sand, melting wax, pendula, cogs, electric current or atomic oscillations. But no one to my knowledge has ever compared one second to another, or recorded the effect of varying quantities on a device, as we are limited to a presumption that movement over the same distance takes the same amount of time. Therefore, we can not even show that this artifice of time runs at one second per second. Notwithstanding 'highly accurate' atomic clocks changing state billions of times a second we are unable to demonstrate that one lot of oscillations took as long as the previous without first assuming the very quantity we are trying to measure. Distance, or rather displacement (an earlier post says change), is the actual observable effect with no tangible evidence to relegate it to mere proxy status for time. Is this a defeat not conceded in the move to redefine time as a distance travelled by light? In what sense then is time a dimension commensurate with space?

Well comparing one second to another is like comparing one meter to another- they better all be the same by definition, otherwise measurement becomes meaningless. Varying quantities of time on a device does have impact- particles move, photons are exchanged, etc. At a small enough level, this all happens quite randomly- we would observe a number of very different states if we were able to examine this device very closely at several different "times". The point is that a second -just like a meter- is NOT absolute: one second of my time will not always be the same as one second of your time, and neither will the distance we measure between any two points we agree on.

Without going into existential philosophy on the nature of reality (that will muddle the content of this post), time as a dimension makes perfect sense. Take the state of our entire universe as it is right now- that is one instant of time dt (there are also, I think, theories that time is quantized- let's pretend it's not for now). One dt later, a number of things will have changed. As we move along this mathematically linear axis, we obtain some 4-dimensional function. Or, if it's easier, one can reduce our 3 spatial dimensions to 2- then, picturing whatever 3-d shape is most convenient, we can stack up "slices" of this 2-dimensional universe to obtain a 3-dimensional shape.
Just as displacement in space is a noticeable effect, I think displacement in time is, arguably, also noticeable. Going back to the graphical model, I can notice my displacement through time by remembering an older time, perhaps when I was in the same place. "x" number of minutes ago, I was sitting here and this white box on my screen was blank. Now, "x" minutes later, it is full of characters. Along the way, if we imagine increasing values of "t" as we go along, we would see me typing this message. The main difference is that time is not physically perceivable- I cannot simply look at something and say that it is a number of seconds long. And also, we can thus far only move in one direction through time.

Permalink In reply to by Anonymous (not verified)

Thanks for the response to my post. May I attempt to clear up some confusion I may have caused by referring to seconds?
We do not have to consider man-made units or different reference frames, I can directly compare any length with any other length relatively easily (in principle at least) but how do I compare one stretch of time with another except indirectly by referring to relative changes in position? Moreover, I do not have to assume spatial relativity, it presents itself to at least two of my senses, but I have to assume there is a temporal dimension and grant it size by measuring something else. Nor should we allow intuition, common sense, and it feels right to guide us in matters of basic reality as they have all proved untrustworthy further back along the chain of existence.

Positing that time is responsible for motion, besides begging the question, rather puts the cart before the horse - we use motion or displacement (in our clocks) to determine time taken not vice versa. Also smacks of conjuring up supernatural forces to explain effects. You say while seated that time passes because stuff happens. But you see different stuff because you are in a different place, by thousands of miles if not more, no matter how tightly glued you are to the chair - the only measurement you can make relating to time is that of the distance you have moved.

As for stating that we move in only one direction through time this is as meaningful to me as someone affirming the presence of the Holy Trinity - there is no witness to either of these scenarios so where did the numbers come from? Perhaps there are three directions in time and only a Holy Unity! Or, more likely, a zero for both.


Time is simply a product of the motion of a mass or energy through space. "Time" isn't anything, it's just a phenomenon we use to measure durations, standardized using radiometric decay. As well, time is relative based on the local conditions of your location in the universe. Photons (processes) occur at differing rates based on gravity, so your speed may not be my speed...:)

Permalink In reply to by Anonymous (not verified)

Old post but I still agree with it. Time is simply velocity x mass divided by the constant (C) the speed of light (T=VM/C). Since light can be stretched and squished, so can time.


What if time is simply a byproduct of consciousness? If the universe is infinite, containing all possibilities, at once, then all consciousness is consciousness of the universe, itself, and the only way consciousness could exist would be for the universe to narrow its "view" of itself to the degree that it cannot perceive itself, as a whole and create an illusion of "me/not me" that would represent the absence of itself and create the contrast necessary for recognition and self-awareness. What if "time" is simply the byproduct of the illusion that "things" exist, separate from other things (and the whole) as its attention moves from one narrow perspective, to another - so that the perception of time is merely a consequence of the illusion that creates the contrast that allows recognition and, thereby, consciousness?

It would also stand to reason, under these conditions, that every individual possibility - be it a thought, a particle or a galaxy - would contain the exact same capacity to allow the universe to perceive itself from that perspective. It would be able to perceive from the perspectives of all possibilities and choose any of an infinite number of possible "objects of attention" from any perspective within each of an infinite number of possible "ranges". Some of which may require a perception of something like "time" and some of which may not.

Crikeys! I swear - that really does make sense, in my head! LOL!

Here is a similar related 'what if'. Since the universe is experienced by consciousness (spirit), it is reasonable that spirit is not of the spacetime energy-matter category. Spacetime energy-matter is like a wind-up toy that is running down (and is pure effect of the big bang). Spirit is the of the opposite category in that it animates and creates highly organized life forms, thoughts, dreams, etc. Spirit is of a create category. If we take spirit to the extreme pure definition (and not as spirit is found in the hybrid spirit-matter form of a human being) then spirit is an infinite creation source whose gentlest touch brings anything into existence. We can imagine that, in pure form, the spirit's creation is without time, and that time is just a peculiarity of this universe. In that pure state, spirit would not experience or have anything in the sense that we have things in a universe with spacetime. In order to 'have' something, spirit would need to differentiate some part of it's creation as 'over there'. And to keep it 'over there', a continuous running series of changes (new but similar differentiations) are needed to get a persistence of 'over there'. If the creation is not sufficiently changing, then it too easily is just an integral part of spirit, timeless and not persisting as per the things of this universe. There is no time for an infinite spirit, but by purposely differentiating some space in a complex pattern of similar states, and associating those states in a sequence of one state coming after another, time is created. Each space that was differentiated is slightly different, in size, distortions, etc. Perhaps vibrations within vibrations such as in elementary particles. Even though each space was created without time (and for ease of thinking, lets just say they are all created at the same 'moment') the spaces are all considered to have a sequence of one 'after' another, and thus they can be 'had' because they persist in 'time'. Time is an artificial association of states of space (experiences) into a progressive sequence that helps to keep space differentiated and persisting.


Time is simply the perception of change in a particular direction... Without consciousness there is no time!


Interesting how many comments there are on this topic!
I will reiterate and try to simplify other posts;
Like distance-measuring tools which use standardized lengths to describe distance, time is standardized motion (Falling grains of sand, number of blinks, atomic oscillations, planetary rotations, etc.) that is used to describe motion.
All the elements of "spacetime" are required to describe motion; x,y,z,and t, which leads me to believe that motion is the basic nature of the uni(?)verse.
I believe Einstein was simply showing that time could not be used as a constant due to differing perceptions of time based on the relative orientation of observers. He suggested the speed of light as a constant and things got screwy when it was found that gravity deflects photons... Hard to find a good vantage point to observe from when your planet is spinning while orbiting a star that is orbiting a black hole that is streaking through the universe...


I don't know what prevents us from concluding that time is the interval between events or it is the sequential order of events. That is, in an isolated system or frame of reference if no events are occurring, time must come to a standstill !

that is just like saying if a tree falls in the jungle and no one around does it make a sound. so assuming we are all alive, and continue to be for the duration time is being considered, no events need to occur except our being alive but cant you see thats the very essence of it. time exists and the tree makes a big racket and we all may give the impression of being dead but are actually alive.


There is intuitive time and there is physical time. Intuitive time is our own sense of time, which results from the rhythmic activity of our brains and body. I doubt it's a coincidence that one heartbeat of the average person is about a second long. It may even be that the duration of a second was based on the heart rate of some important individual (king, emperor, revered philosopher, etc). Virtually every animal, especially predators, must have an intuitive sense of time because a lung needs to be timed, a pursuit trajectory has to be timed in order to meet the prey in its trajectory. Our intuitive sense of time is also dependent upon memory. The charging predator has to remember what it felt and saw a split second prior to now in order make a correction in its trajectory. We are most aware of time when we remember past events. Because of this, we are seduced into thinking that time has an objective reality. It does not.

What we would call physical time is the time we think we are measuring with our clocks. But all we are really doing is substituting a more consistent device for our heart, our firing neurons, our memory, the movement of the sun's shadow on a sundial, the cycles of the moon, etc. All we are doing with clocks is establishing what we believe is a cyclical device that is highly consistent--a standard. And then we measure all other movements of matter and energy in space as a ratio of the object's distance traveled to the "distance" traveled by the clock, i.e., velocity. I say "distance" because many clocks we have developed have no moving parts.

But how did we establish a system for determining, to a high probability, that a particular device or process is highly consistent? There are at least two ways: By converting its cyclical output into a linear form that can be measured with a "yardstick"--a measuring device that is consistent and objective. A cyclical output can be fed into an electronic oscilloscope which would display it as a sign wave. Observation and measurement of many cycle lengths can establish its consistency. Another way is to make a large number of physically identical devices which, when operated, would be initially synchronized, then observed over many cycles and note taken of how much a-synchronicity develops among them. None of these processes are dependent upon a preconceived standard of time. In fact, what we have developed are highly consistent standards of movement to which all other movement are compared.

Permalink In reply to by Anonymous (not verified)

The word I intended was lunge, not lung, obviously. Also, it's supposed to be "sine wave" not "sign wave".

Addendum to my post:

One might ask, why cyclical movement rather than linear movement? There were at least three types of linear measure used in the past: A burning rope with spaced knots, a burning candle and dripping water. These have obvious drawbacks. On the other hand, a cyclical standard does not need to be consumed, and the beginning and end of a cycle remains within close proximity to the observer.

To expand on my statement that some clocks don't have moving parts: Mechanical parts, yes. But even electronic clocks function by means of the movement of energy and matter. Electrons move through circuits, Logic gate resistance changes when an electrical potential is present or removed, which is movement in the atomic structure, even though slight.


A query which puzzles me:
(1) In Einstein's Clock shown moving through Space, the light is shown travelling vertically between the moving mirrors. Since the light travels through Space independently of the Clock and will receive no impetus from the movement of its source, from whence does it get the same magnitude and direction of movement relative to external Space as the mirrors? Therefore why does it not appear to move rearwards over a longer path relative to the mirrors rather than being carried forwards relative to the stationary observer?

Permalink In reply to by Arthur Morris

The unstated premise of the thought experiment is that the light ray's movement IS dependent on the movement of its source. If it was independent of the speed of the source, then the observer on the train would detect a shift in the contact point relative to the emission point. This is not observed when the source is moving at constant speed. But it is observed when the source is accelerating.


Time is the matrix of information permeating space. There are many subjective interpretations that describe different and similar aspects of the phenomenon that lies at the basis of reality. This is my opinion.


- I have a few thought about your reflexions about Time:
What if ‘time’ does not exist:
What we call speed or velocity is not the rate of change of distance with respect to time, but simply the change of position with respect to Space.
Objects do not move over time (because time does not exist). Objects simply move in Space. This started with the big bang.
What we perceive as time is a product of our minds which have the capacity to :
-retain mental images of positions of objects that we have observed.
-extrapolate the positions of objects if they continue on their existing paths
The concept of 'time' is thus purely an abstract idea that we humans have introduced to explain the fact that we observe positions of objects changing.
The fact that objects move and interact with each other is surely sufficient to explain all the phenomenon we observe in the universe without need for the concept of time.
At the Big Bang, objects and energy start moving in Space, and that movement resulted in all states of the universe that have been observed. There is no need for ‘time’ to explain this, just the laws of nature together with motion through space.
This would mean that time travel does not exist (because time does not exist).
However, we could re-visit any former state of the universe simply by putting all the objects in the universe (down to the molecules, and sub-atomic particles in our brains) back in the positions they held in space (with the same momentum, energy etc.. that they had when they were in those positions).
And, to create any ‘future’ state of the universe we simply need to move all objects in it to the place that we extrapolate them to be in at a later state of their motion through space.
The only barrier to this kind of ‘time travel’ is that in practice it would be difficult to move all that stuff (everything in the universe) to its previous or expected position.
Thus, time does not exist – If I want to go back to a 'time' when my Mother was alive, for example, all I need to do is move particles to the correct positions in space corresponding to that state of the universe.
If I simply did that, she and I would inevitably be having the same thoughts, and memories as we had the first time. And we would effectively have travelled back in what we call ‘time’ but which is, in fact, just a previous position of objects and energy in space.
Maybe it would simplify the equations of cosmology and quantum mechanics if we re-visited them from the perspective described above.
- I would be very interested to know what you think about the ideas I have expressed above.

I cannot agree with you more. Time does not exist! It is a human conception and not a universeal truth. There is no such thing as "time" as we humans know of it or as we precieve it. There only sequences of events in this universe, but time itself is not real. If event A has happened, then it happened. If event A has not happened it hasn't happened. Many people believe that if events A is to happen it must happen at a particular time but I think whether event A happen at 11:00 or at 11:01 pm generally speaking in a cometic level doesn't really matter. Like Energy is a scalar rather than a vector and that it is the start and end states that are the most important, I believe this to be true for all events in the universe. As long as events A, B and C happens in the correct sequence then the actual so called "time" as we knwo it is not important. In fact, as long as this sequence of events A, B and C happens and happens in the correct order than it can even happen as a whole sequence in a completely "time" and it could very well not matter. The time that is precived by humans is exactly that a human concept (based roughly on the earth orbit around the sun) and has no true universal value.
Time then some would say has more to do with the expansion of the universe since the Big Bang. This is equally as valueless as human's preception of time.
Case I: If the Universe is not expanding but rather it is static. If this is true then Time in the sense of the start of the universe to the end of the expansion of the universe would be meaningless as the universe is static and no expansion is ocurring. What difference does it make how long ago the Big Bang was if the universe is static? Hence unless we can clearly prove that the universe is NOT static there is always the chance that Time based on the expansion of the universe is meaningless.
Case II: The universe is expanding. If the universe is indeed expanding then we must further subdivide our concederations into two sub categories. Caterory A: The universe will continue to expand until all entropy has become chaos and nothing is orderly anymore and the universe will then just stop. Thus as mention before this would make Time meaningless and valueless as once entropy is totally lost time itself will have no meaning. Furthermore, if the entropy of the universe is not decreasing at a fixed rate then the concept of Time based on the expansion of the universe is hard to define as Time itself would not be linear and Time in the so called past would be different than the Time in the so called future. Category B: The universe is expanding and at some point will lose all entropy and due to some mechanism begin to collaspe upon itself. In this case, what is the value of this so called concept of time? All that moves "forward" will be undone by the "backwards" movement of the universe and if this expansion and contraction is cyclic than really who knows how many cycles "this universe" have gone through. If for example this is the 1,000,000,000,000th cycle of expansion of this universe then the so called minutes, hours and years that we track of this current's universe expansion is insignificant in the larger scheme of things for the universe. For the universe, time is not important. Time is only important to humans and hence it is only a precieved quantity of our minds.
Case III The universe is not static not is it expanding it is constantly shifting and changing hence giving us the preception that it is expanding as we have not lived long enough or have observed the universe as we know it long enough to tell the difference between a changing universe versus an expanding universe. If the universe is shifting and changing rather than expanding linearly then once again the concept of time is difficult to define as time at one position will be different than time when the universe have shifted to a different position.

With the above arguements than it can further be said that then time travel is also not real. There is no such thing as moving forward in time or moving backwards in time. If the universe is indeed in a cyclic expansion and contraction witht he possiblitiy that "new" universes starting with "new" big bangs" can be spawned at slightly different locations than its previous universe or maybe multiple universes are constantly in f a flux of expansion and contractions than the idea of moving forward and backwards in time would be incorrect but moving "sideways" from universe to universes could preceivably allow an object to reach a similiar but different universe that is at a different expansion point than our own and thus allowing for the so called "forward" and "backward movement in "time". When in fact, it is a sideway movemet to different location points within a sequence of events in those universes. Just as an electron can travel between different quantum states or quantum universes other objects under the right condition can travel sideways to different universes and at some location down the road collaspe back to one quantum universe acting as a node between these universes.

Lastly, to address the idea that time is merely the "space" or "interval" in between events - though this would be something I can agree with in principle, in reality it is not useful. As with my point about energy and energy states, the path of the object is not important and thus the time interval between events are also not important but rather the end states of that object and its event is what matters the most. If we then add the possiblity of different quantum states or universes in there then the so called precieved "interval" between events can much much more complicated than the mere "seconds" that elapsed in between two events. That so called interval could be elapsing through various universes and or quantum states and the "interval" between event A and event B could actaully be very different interval at various occurances of event A and event B depending on the transverses of quantum states and or universes at different incidences of events A and event B. The seemingly simple and straight forward "interval" we observe can in fact has many many different variations. I compare this to when people first start to learn about math. Because all they know about is linear one dimensional things they falsely believe that 1+1 is always equal to 2; howvever, as they expand this knowledge and observations they then realize that if they are adding a 1 unit vector to another 1 unit vector the resultant can be 2 but it doesn't have to be as the resultant depends on the directions of the two vectors. The same then can be said of this concept of "interval". We observe this "interval" in our single universe, but what if in fact it turns out that this "interval: actually transverses multiple and varying quantum state and or universes then the "interval" we "measure or label" could only be ONE of the many other possible "resultant intervals".

Until we as humans can have some sort of definitive understanding of how the universe truly behaves, then the concept of time is nothing more than a concept humans use in our human attempts to calculate the world around us based on static single universe formulas like d = vt. Which brings me to the my ending point that in reality I think scientist are wasting their efforts in their quest to better understand the workings of the universe from a "time dependent" perspective and should instead focus solely on the enegy state and energy signatures of objects and study their energy and not quantities based on or dependent on time. Abandon the concept of time in our quest to understand the comos and we would actually make further advances in our understandings.

Jimmy Wu

Here's a thought experiment for you. Let's say you are driving on a road that crosses railroad tracks. A train is coming. You're feeling confident that you can beat the train to the crossing. If you speed up enough, you win, but if too little, you lose. Velocity is, of course, distance traveled per unit of time in a particular direction. Is this a good time to assert that time doesn't exist, and therefore, speeding up is meaningless? If time doesn't exist, are you even moving? Is the train even moving, or are you just imagining it? But the cleanup crew will be absolutely sure that both the car and train had velocity. And the timing was terrible.

John Longman you got it in one. All this garbage about time and the universe is absolutely idiotic. Newton knew it and Einstein tripped over time. Time is just a man made measurement. But what does it measure? Newton knew the answer and so does John Longman. I don't know why you go int onto the Big Bang thing and time travel except to say that it is not possible because nobody can wind back the universe and put every particle that existed back where it was back then. Impossible.
Love your work and it is good to see that there are some people who can still think for themselves and "still perceive the web they weave... keep on thinking free."
(A quote from the Moody Blues)
The Voice


If time does not exist, then what of the saying that 'no two objects can occupy the same space at the same time'. The obverse of this is that 'two objects can occupy the same space, but only at different times'. We know what happens if we try to force this state of existence--an explosion! If time does not exist, how can we make sense of this observable fact?

It seems to me that time exists because events do not occur instantaneously. An occurrence of any kind depends on the transfer of energy from one object to another or from one point in space to another. The fact that energy transfer is not instantaneous is not only based on scientific measurement, but also by inference--the universe would not exist if energy transferred instantaneously. All there would have been was a Big Bang, then a Big Snuff.


Time for a drink


You may well be right. However, I think the fact that two objects cannot occupy the same space at the same time, is more to do with the nature of objects, rather than the nature of time or space. The fact that 'an object cannot occupy another object' is surely the underlying and more fundamental truth, and that remains true even if we do not consider time or space.
And indeed, the movement of matter relative to space is not instantaneous, but does that require Time? Or, would it be enough to accept that the displacement of matter and energy in space takes place gradually and variably. ‘Motion’ exists, and objects have previous and predicted positions. The Big Bang started things moving with respect to the origin, but did it also create Time? Or did we invent the idea of time to help measure and compare motion, introducing 'past' and 'future' for practical purposes. Is Time simply an abstract concept that we invented to explain what we observe? We can move around in space, and we can touch and feel matter and energy. But Time is very abstract – we exist permanently in the present. We talk about the ‘past’ and the ‘future’ but we cannot access them from the present, other than possible by moving objects and energy of the universe back to previous or anticipated positions and states.
To make a loose analogy: we know that people have features on their faces, and we invented the notion of ‘Beauty’ for practical purposes, and so that we could, agree upon, compare, and talk about different arrangements of facial features that please us. We know that noses, eyes, etc. exist, but ‘Beauty’ does not exist in the same way. It is abstract. Could not Time be similar? We know that matter, energy, and space exist, because we experience them directly. But Time seems to be an abstract mental concept which we use to help us explain and compare the way in which matter and energy are evolving across space.

I can say I totally agree with you. Time is a scale we humans invented by observing cyclical phenomenon in order to measure movement and natural reactions.


If a black hole crunches time, I imagine a reverse black hole would speed time up. Can anyone elaborate?


I am sure this is well discussed sonewhere, but why can't time be an emergent prooerty of objects and their motion? The perceived arrow of time seems well related to the fact that a partice or wave have some direction to their relative movement.

Time is like a winding river. Its shape taken by the relative differences in movement between objects. Objects that have more velocity (someone that flies in an airplane) compared to objects that stay still (a monk), means time passes quicker for the the person or object with frequent velocity. This doesnt mean time moves backwards for the monk, but instead it means the time stretches to allow for velocity within the the same time line. More importantly, time is not endless, instead it is stateless and we simply move through it rather than time moving. in other words, time is fixed and we percieve it by various means of measurements. The arrow of time is just the arrow of our own perception.


A Thought Experiment from “RELATIVITY: THE SPECIAL AND GENERAL THEORY” by Albert Einstein
“..in reality (considered with reference to the railway embankment) [the observer] is hastening towards the beam of light coming B, whilst he is riding on ahead of the beam of light coming from A. Hence the observer will see the beam of light emitted from B earlier than he will see that emitted from A. Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A. We thus arrive at the important result: Events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa (relativity of simultaneity). Every reference-body (co-ordinate system) has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event.”

>the [moving] observer will see the beam of light emitted from B earlier than he will see that emitted from A.<
I think this statement is ambiguous.
This “moving observer” will not see the “Actual Event Flash B” occur earlier in time but will merely be receiving his electro-magnetic evidence of “Flash B” before receiving his evidence of “Flash A”. If the speed of light was infinite then both observers would see the Flashes occur simultaneously whatever their velocity and wherever they happened to be -and all events elsewhere as and when they occurred!

>Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A.<
I think this conclusion is erroneous.
Because the observer on the train receives the evidence from one flash before the other can indicate nothing unless he knows the two distances separating his present location from the point in Space where they occurred. Einstein says it is the movement of the observer that affects simultaneity but why does he not consider the case where the moving observer starts from a point along the track closer to Flash A so that he arrives mid-way between the Flashes when the two beams meet? In this case he, though still the “mover”, will also see them occur simultaneously. Non-simultaneity is a function of an observer’s position in Space.
What makes the track stationary? The track could itself be the “mover” in the opposite direction, in which case the train decelerates and becomes stationary. Einstein offers no definite meaning for “stationary”.

>Every reference-body (co-ordinate system) has its own particular time; unless we are told the reference-body to which the statement of time refers, there is no meaning in a statement of the time of an event.<
Whilst I would agree that every observer has his own particular relative timescape I maintain that this is fixed by his particular relative position in space AND that there is a meaning to “the time of an event”. Everywhere I look is “ago”, in the Past, and the further away I look the more “ago” it is. The clock I see on the wall across the room I actually see as it was about 20 nanoseconds “ago”. I see from my “Here” the Sun as it was about 8 timeseconds “ago”, shining from an observed position “There” in Space, -whereas it is “Now” about 2 arcminutes further westward from my observation of its position.

Visual and Aural Perspectives: Here-There and their corollaries Now-Then.
The appearance Here (to the eye/ear) of the relative positions There in Space of objects/events.
The appearance Now (to the eye/ear) of the relative positions Then in Time of objects/events.
Suppose there was only sound and no light. How would this affect our knowledge of Then in Time? Sound travels at a fairly constant speed through still air. Suppose two different church clock bells ring the hour together. An observer sat mid-way between them would hear them strike simultaneously but an observer on the move may not. If the moving observer heard them ring separately is it sensible for him to assume they did so at different times because he was “moving”? An effect that would simply depend on his relative separation from each bell at the moment he heard it. Of course, by being able see the (almost) instantaneous light result of clock faces that show the same time (give or take some nanosecs), and recognize that any difference in delay in the aural perception was because of differences in distance from him.

Relativity states that Time dilates and Length contracts for a moving observer. But moving with respect to what? In explanations of the effect (eg. explaining the Twin Paradox) the experience of a stationary observer is compared to that of a fast-moving one. Einstein uses platforms and tracks in his Thought Experiments, but what and where is the “stationary reference” in Space? Could a possible candidate be a point in Space from which light has radiated equally in all directions?

Pursuing this idea I suggest a scenario as follows:
In remote Space an observer “O” creates a brilliant Flash (“O” and “F” in my diagram: see Note 1. below) to emit a pulse of light radiating in all directions. The Flash site becomes a fixed point in space and time, because it is at the centre of an expanding bubble of light-data moving equally at “c” in all directions.
“O” immediately moves away from this central point F at a velocity of 0.5c in a straight course, then somewhen later immediately reverses at 0.5c to return to the site F . My diagram shows four subsequent ‘snapshots’ of ‘events’ with elapse of time shown by the expanding distances the pulse bubble has travelled away from F divided by “c”.

EVENT 1. Shows “O” somewhere on his outward leg. Throughout this outward leg the speed of separation of the pulse straight ahead of “O” is reduced to 0.5c.

EVENT 2. Here “O” stops and instantaneously reverses.

EVENT 3. On his way back to the original position. On this return leg the apparent light speed is gradually being restored to its normal velocity of “c”.

EVENT 4. Back at the site of the original Flash with the pulse at an undistorted “c” in every direction.

My puzzle is that if Relativity’s Time dilation/Length contraction works on the outward journey in maintaining “c” with respect to the separation between “O” and the pulse going ahead of him, how does it also work for the separation of “O” with the light pulse as it goes in other directions?
It seems on his outward journey the speed of separation between “O” and the pulse going in the diametrically opposite direction requires exactly the opposite corrections, viz. Time contraction/Length expansion. And there is always one angular direction, (marked “C”), which requires no corrections at all. Yet there can only be one observed clock rate & length scale for “O”.

Red/blue shifts.
In dilating time and contracting length to restore apparent relative light speed to “c”, would not these same “scales” similarly restore the apparent wavelength distortions and remove Doppler red/blue shifts too? But we do see these.

Note 1. My diagram.
Sorry! I just cannot reproduce the visual image of my diagram in your comment box. (I’m an old man of 95 struggling with modern technology on a 10” Tablet).
This is a link to it: https://goo.gl/photos/pY9gPp77MMbXnupV8
I have also posted this whole Comment on my WordPress blog seesomelight.wordpress.com but even here I could only get the diagram right at the top of the text.
Alternatively I think I can email it successfully from aremo14@yahoo.co.uk
Arthur Morris Eastbourne BN23 7PY


Here's my put : Time is a measure of a system's change of configuration or state unrelated to any single identifiable event.


Time is what we call the ticking of a clock, but the ticking of the clock is merely motion. The fundamental character of the universe is motion. It came into existence with the BB because that's what the BB was, motion. I would guess that if the universe were to cease expanding, it would cease to exist. Another way of putting it is that all motion within the universe, right down to the sub-atomic level, is derived, made possible, from the expansion of the universe. It seems logical that if all motion ceased to exist, all matter and energy would cease to exist as well, since motion is fundamental to the internal dynamics of all matter and energy. But, in fact, the universe can't stop expanding.
We are told now that the rate of expansion is greater at large distances than at nearer distances. I wouldn't call this an acceleration of expansion, but an acceleration of collapse. It could be that the universe blew through an enormous black hole in another universe upon it's creation, and is now heading toward it's own enormous black hole of annihilation. We see this as an expansive movement, but probably because of a distortion in our perception of space/time. This idea would need to be studied by someone with a much greater mathematical talent than I have.


I am not a mathematician but am troubled by many of the basic mathematical assumptions and their implications for the universe. I always saw time as the succession of physical events, say cogs going round in a clock or planetary revolutions around the sun. You time your egg at 4 minutes assuming the regularity of the watch spring or pendulum. Succession implies an order and therefore time's arrow seems part of the definition.
If this is the case (I am neither physicist nor mathematician), is it conceivable that any two physical events are absolutely simultaneous? If you were observing what might seem like simultaneous events, say a car driving through a red light would it be theoretically possible to distinguish minutely between the time you receive the light data of the car and the light data of the traffic light even though it forms one coherent picture in your apprehension of the event?
Perhaps I read too much Ballardian sci-fi as a young man, but if everything we experience around us can ultimately be broken down into imperceptible discrete "events" then you could view no two events as synchronous. Perhaps I don't understand Einstein's thought experiment of the torch beam in the train, but his platform observer surely sees the light events in the same order as the passenger, or is he saying that the man on the platform can see more intervening events during the passage of the light beam from the torch to the carriage ceiling?