# Do we know exactly what time is?

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#### Ethos_

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##### Re: Do we know exactly what time is?
« Reply #50 on: 15/08/2014 15:41:02 »
Quote from: Ethos_
And as well, the term Past has no meaning without the memory of it which occurs in the Present.
I disagree. To a small extent the past can be deduced from causality as well as memory.
You make a fair point here Pete, causality is the foundation for the deterministic world view. But in the quantum realm, physicists discard that view in favor of the probabilistic one. I must ask: If we are to trust causality, how deep into the Planck realm does it reach? And even more importantly, how far reaching does the probabilistic effect the information we collect about the past? I'm not sure we can establish exact limits on either case at this point. When taken in total, how probabilistic are world events, and how does that influence how much we trust causality and the connection between the past and the present?
« Last Edit: 15/08/2014 15:50:35 by Ethos_ »
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#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #51 on: 15/08/2014 22:12:10 »
People mention the Planck scale as if it is an absolute invariant and Planck time the smallest unit. If a photon moves 1 Planck length in 1 Planck time then all other matter, still being in motion must move less than 1 Planck length in 1 Planck time. Also their particular time frames must be a subdivision of 1 Planck time. Else they would be stationary during one transition state of the photon and I truly believe that nothing can ever be stationary in relativity.

#### Bill S

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##### Re: Do we know exactly what time is?
« Reply #52 on: 15/08/2014 22:47:02 »
If time is quantized, and if Planck’s time is the quantum, then nothing can make a move that that is less than one unit of Planck’s time in any length of time.  Compare this with the quantum leaps of electrons between energy levels in an atom.  The only way in which two electrons can appear to take different lengths of time to make the same leap is if one remains longer in the first energy level before making the leap.

Transfer this thinking to objects moving through time.  If time is quantized, motion through time takes place in a succession of jumps. The only thing that appears to move smoothly through time is EM radiation.  Everything else moves more slowly, so it pauses between jumps, and these pauses become longer as things move more slowly.  Even with very slow moving objects, these pauses would be too short for us to observe them.

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #53 on: 15/08/2014 22:57:25 »
Think of a photon which is several Planck lengths away from an electron during the process of absorption. If the electron cannot move then the photon would have to come to a dead stop and wait for the electron to react. The photon wants to travel one more Planck length but the electron wave is 'in the way'. How do we reconcile this conundrum?

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #54 on: 16/08/2014 11:54:24 »
We have light at $$\frac{1 * lP}{1 * tP}$$. Now any other particle that is not a photon or hypothetically a graviton cannot attain this speed. So how do we proceed? We can say that our electron, if we have quantization, cannot reach $$\frac{1 * lP}{2 * tP}$$ easily as this is half light speed. So it should be a speed defined by $$\frac{1 * lP}{n * tP}$$ where we don't know what n is. The only other possibility is applying a factor to the Planck length as well as the Planck time. In which case we no longer have a definitive boundary to quantization. If quantization is to be maintained this seems to indicate a separation between space and time. I am wondering about the massless photon, its kinetic energy and angular momentum as to whether or not it should impart enough energy to an electron to move it far at all.
« Last Edit: 16/08/2014 12:09:50 by jeffreyH »

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #55 on: 16/08/2014 12:24:54 »
Another conundrum lies in the interaction between light and either the medium it is traveling through or a gravitational field acting on the photon. The photon now no longer travels 1 Planck length in 1 Planck time. The ration between Planck time and Planck length in this scenario also appears to indicate a separation between space and time. We can use the calculations for time dilation and length contraction to reconcile the gravitational field situation but other considerations come into play regarding the medium through which light travels. Could the photon have a residual charge? Would this charge have an effect on the space-time relationship?
« Last Edit: 16/08/2014 12:26:39 by jeffreyH »

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #56 on: 16/08/2014 12:28:38 »
If the photon did have a residual charge and this was negative then the photon would effectively slow down when approaching very close to an electron and this would resolve the quantization problem.

#### Ethos_

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##### Re: Do we know exactly what time is?
« Reply #57 on: 16/08/2014 14:33:12 »
Another conundrum lies in the interaction between light and either the medium it is traveling through or a gravitational field acting on the photon. The photon now no longer travels 1 Planck length in 1 Planck time.

From my understanding, the photon always travels at 1 Planck length in 1 Planck time. The reason it appears to slow down is, when in any medium other than the vacuum, the photon will be absorbed and then subsequently re-emitted. This interruption in the photon's path has the appearance of slowing it down. But in truth, the speed of the photon from one absorption to the next is still c. Between each interruption the photon still travels at light speed, 1 Planck length in 1 Planck time.
« Last Edit: 17/08/2014 00:12:00 by Ethos_ »
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#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #58 on: 16/08/2014 17:27:53 »
Another conundrum lies in the interaction between light and either the medium it is traveling through or a gravitational field acting on the photon. The photon now no longer travels 1 Planck length in 1 Planck time.

From my understanding, the photon always travels at 1 Planck length in 1 Planck time. The reason it appears to slow down is, when in any medium other than the vacuum, the photon will be absorbed and then subsequently readmitted. This interruption in the photon's path has the appearance of slowing it down. But in truth, the speed of the photon from one absorption to the next is still c. Between each interruption the photon still travels at light speed, 1 Planck length in 1 Planck time.

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #59 on: 16/08/2014 21:46:27 »
Reflection and refraction follow definite paths. The angle of refraction must be preserved throughout any absorption and re-emission cycle. This is the concept I have a problem with. Application of the uncertainty principle should mean that this path deviates and yet it doesn't.

#### Ethos_

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##### Re: Do we know exactly what time is?
« Reply #60 on: 17/08/2014 04:39:12 »
So,..........what is time according to Einstein?

Quote from Albert Einstein: "The distinction between the past, present, and future is only a stubbornly persistent illusion."
« Last Edit: 17/08/2014 04:46:40 by Ethos_ »
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#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #61 on: 17/08/2014 11:18:31 »
So,..........what is time according to Einstein?

Quote from Albert Einstein: "The distinction between the past, present, and future is only a stubbornly persistent illusion."

He is right with respect to time being a human invention used to explain change. The state may change but the contents don't. You could look at time as the current state of all the waveforms in the universe regardless of how long it has taken them to get to that state.
« Last Edit: 17/08/2014 11:48:20 by jeffreyH »

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #62 on: 17/08/2014 11:58:50 »
When looking at the Planck scale all we can say is that time relates to change at that scale. Even then we say it may be multiple Planck times before a movement of 1 Planck length is achieved. So we are modifying time without a modification of space. This shows the absurdity of the Planck dimensions as we see them. Time and space according to relativity change in tandem. We have to adjust both the Planck length and the Planck time to marry quantum mechanics and relativity. Now thats a scary thought because then there is no absolute measure of quantization.

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #63 on: 17/08/2014 12:05:38 »
However, if the Planck length and Planck time are modified under gravity due to length contraction and time dilation then the singularity of a black hole could be explained in relativistic terms. I have no idea how this would work mathematically as it complicates both quantum mechanics and relativity.

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #64 on: 17/08/2014 12:25:24 »
Could it be that there is no background geometry in relativity precisely because of a modification of the Planck scale by gravitation? Whereas length contraction on a macroscopic scale appears flat locally at the Planck scale there would be a curvature in this contraction.
« Last Edit: 17/08/2014 12:27:56 by jeffreyH »

#### jeffreyH

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##### Re: Do we know exactly what time is?
« Reply #65 on: 17/08/2014 12:47:07 »
It just struck me that the Planck scale should be tied to the event horizon of a black hole where it will be of a consistent value because of its relationship to light. Everything then is relative to this point.

#### petm1

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##### Re: Do we know exactly what time is?
« Reply #66 on: 17/08/2014 22:52:15 »
Quote from: petm1
Space and time, opposites yet the same.
Woa! Where did you get that notion from? It's certainly not true. While in some respects space and time are treated on the same footing in relativity mathematical, it's certainly not true that their anything alike physically, that's for sure. Space is what you measure with a rod. Time is what you measure with a clock. You can go back in space but you can't go back in time. You can rotate one spatial axis (i.e. a rod) into another spatial axis but you can't rotate a rod into a clock.

Let me quote something Einstein said about this. From A Brief Outline of the Development of the Theory of Relativity by Albert Einstein, Nature, Feb. 17, 1921. page 783
Quote
From this it follows that, in respect to it's role in the equations of physics, though not with regard to its physical significance, time is equal to space coordinates (apart from the relations of reality).

Quote from: petm1
Photon is unchanging in time..
That too is also untrue. A photon moves through space and its phase changes with time. You're thinking about transforming into a photons frame of reference and making measurements there with a clock and comparing it to the photon's frequency, etc. However since it's impossible to do that you can't even speak of it. Therefore the only time that you can speak of regarding a photon is coordinate time. Just because you can't speak of a photons proper time it doesn't mean that it's unchanging. You'd never be able to step into a photons frame of reference to verify it and that's not science.

If emission only happens in the present then as an observer and being a receiver means that which ever direction I look I am seeing the past.  The longer the photons travel time the longer the distance the further back in time you are seeing.  This kaleidoscope from the past I see as my present is described using a signature of either +++- or ---+ opposites to describe the same thing.

Does E=hf change during a photon's lifetime other than as a measure for the expanding space in which it travels?   Or in the case of a gravity well, where we do not think of space expanding, do you think it may be time that is changing the red shift of our rulers?

#### mxplxxx

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##### Re: Do we know exactly what time is?
« Reply #67 on: 27/10/2014 07:44:09 »
My take on time is that it is just a concept. Two types of time are postulated by physics. Global (or absolute) time is the same everywhere, although its exact nature is vague. It gives rise to the present.  Relative time, as postulated by Einstein in his theory of relativity, is time that passes at different rates for objects moving at different speeds. Personally I think the universe is timeless. In other words we exist in an eternal present. The only type of time that exists in this universe is reaction time. This is the time a reaction takes and is related to the amount of energy available to the reaction and the distance the energy has to travel during the reaction. Thus, distance and time in this scenario would seem to be equivalent (sort of) – especially considering the speed of light is a constant.

By the way, relativity states that the speed of light is a constant and uses this fact to postulate that time passes at different rates depending on the speed an object is moving. The theory seems to fail to account for the fact that light does not have momentum, never stops, never accelerates, and whose quantum nature is poorly understood. Put another way bosons (light e.g.) are quite different objects from fermions and relating the two via by time may just not work.

#### phyti39

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##### Re: Do we know exactly what time is?
« Reply #68 on: 29/10/2014 18:42:49 »
Here is food for thought, while I put on my waders.

From 'The Meaning of Relativity', Albert Einstein, 1956:
page 1.
"The experiences of an individual appear to us arranged in a series of events; in this series the single events which we remember appear to be ordered according to the criteria of "earlier" and "later", which cannot be analysed further. There exists, therefore, for the individual, an I-time, or subjective time."
page 31.
"The non-divisibility of the four-dimensional continuum of events does not at all, however, involve the equivalence of the space coordinates with the time coordinate."
page 32.
"Finally, with Minkowski, we introduce in place of the real time co-ordinate l=ct, the imaginary time co-ordinate..."

From "On the Electrodynamics of Moving Bodies", A. Einstein, June 30 1905:
par 1.
The pointing of the small hand of my watch to 7 and the arrival of the train are simultaneous events."

The author of SR didn't believe or promote the idea of an objective time. In contrast, he developed the idea of clock time or time measurement as being motion dependent! It was Minkowski who expressed the time variable as a mathematical 'dimension', but solely for mathematical purposes, as noted above.

Subjective time requires memory as mentioned in the first quote, which allows a comparison of a current state to a previous state for any changes, which lends itself to an interpretation of time flowing. Patients with brain damage to specific areas involved in maintaining a personal chronology, lose their ability to estimate elapsed time, short or long term. Consider the fact that people waking from a comatose state, have no memory of how much elapsed time, whether hrs, days, or even years.
Consider one of the greatest misnomers ever used, 'motion pictures' or  'movies', where a person observes a sequence of still photos and the mind melds them to produce moving objects where there is no motion.

The simplest argument against the arrow of time, time is a scalar, a magnitude with no direction.

The operational definition of assigning a time to an event as mentioned by A.E. in the 1905 paper is essentially what it is, and how it's been done since humans appeared.
It is a correspondence convention, i.e., assigning events of interest to standard clock events, a measure and ordering of activity, with 'time' always increasing/accumulating.
It is an accounting scheme developed out of practical necessity, for human activities like agriculture, business, travel, science, etc. The unit of measure for time initially referred to relative positions of astronomical objects, stars, sun, and moon, which implies earth rotations and earth orbits. The year equates to the periodic motion of the earth relative to the sun, the month, the moon relative to the earth, and the day, the earth rotation relative to the stars. All units of time are by definition, involving spatial motion or distance. The clock further divides the day into smaller units of measure. The reference in the 1905 paper of the watch hand to a position on the watch face involves nothing more than counting hand cycles (hand motion of specific distances representing subdivisions of a day). Finally, with the present day light clock, with internal light oscillations between an emitter and a mirror spaced a distance d, the time t represents a quantity of light motion equal to 2kdc, i.e. a distance labeled as 'time'.

In the world of quantum physics, suppose a particle can have three states, a, b, and c. Suppose the first three observations record abc, and the second three record cba. Did time 'flow' backward?  No, and we have proof, since the 'time' of each observation was recorded. It was just a reversed sequence.
Flipping a coin is governed by the rules of physics, yet the results are independent of time. The probability of H or T is always 1/2.
If an object is dropped from a height, next to a vertical measuring stick, and recorded on video, analysis of the video allows a mathematical relation to be formulated between the time stamp of each frame and the height of the object, like (h = h0 -.5gt2). Notice that verification of the experiment requires a clock, since measurement is the modus operandi of science. More importantly notice, gravity, not time, causes the object to fall, and the clock is just a means of ordering and relating the events.
To bury the idea of time (as we know and use it) as a causal factor, note that the time of an event is assigned after perception of the event.

Nothing like an objective 'time' has yet been discovered, but that doesn't imply it doesn't or couldn't exist. Consider all the 'fundamental' particles that were discovered, once the appropriate experiment was designed.

#### JohnDuffield

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##### Re: Do we know exactly what time is?
« Reply #69 on: 30/10/2014 13:24:01 »
..."The non-divisibility of the four-dimensional continuum of events does not at all, however, involve the equivalence of the space coordinates with the time coordinate"...

The author of SR didn't believe or promote the idea of an objective time. In contrast, he developed the idea of clock time or time measurement as being motion dependent...
Good stuff phyti.

#### David Cooper

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##### Re: Do we know exactly what time is?
« Reply #70 on: 30/10/2014 19:11:45 »
Whatever time is, it has to keep order in the way things come to be the way they are. If you smash a plate into fragments, it is clear which way the events occur in because starting with fragments and having them come together to make a plate doesn't work. It would require the initial fragments to be designed carefully to make all the shapes and broken surfaces match up, it would require all the pieces to be flung in the right initial directions at the right speeds and with the right orientations, and it would require all the broken surfaces to be able to rearrange their bonds in such a way that all the pieces could fuse together perfectly. The same applies to any complex happenings where there are multiple causations feeding into new events which become part of the cause of future events.

This is the "arrow" of time business, but it's more than a mere arrow, for it sets out an order in which arrangements of stuff exist. Even if you imagine that the past arrangements continue to exist such that past, present and future are all eternally stored in a kind of block, the past parts of it must have been laid down before the present and future ones because if the later ones were not created later than the earlier ones, there cannot be any causation from the earlier ones to dictate the form of the later ones - the apparent causation becomes nothing more than coincidence, and it would be a coincidence of such magnitude that the word "astronomical" is almost completely useless even as a component of the description of the unlikelihood of the apparent causation existing in the block.

If there is real generation of the future from the past so that causation can be real, then there is a kind of time that flows; not a mere arrow.

It would be perfectly possible to imagine that the universe exists as an eternal block in which we can move forwards or backwards in time to experience it from different viewpoints, and in doing this we would be exploring an eternal block universe in which past, present and future all exist in a timeless way, but when you try to account for the existence of that block universe, you hit the problem that there would have to be an earlier phase in which it was generated starting with the far past and ending with the far future, all the construction done under the governance of some kind of flowing time which would allow events to be rolled out in order of causation. The alternative is to believe that there is no causation written through it at all and that all the patterns of apparent causation are down to nothing more than chance because there was no opportunity for causation to generate future arrangements of the content of the block from past ones. That would be to believe in something so unlikely that the word "ridiculous" is likewise incapable of expressing more than the tiniest hint of the scale of it.
« Last Edit: 30/10/2014 19:25:34 by David Cooper »

#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #71 on: 02/11/2014 11:28:13 »
Depends on definitions phyti. Time is locally unchanging for each observer in my thoughts, you do not gain more life by sitting on a event horizon for example, observing a universe die. That's why we all live and die, doesn't matter where or how fast. The other comparisons is between frames of reference, and there NIST has proven time dilations to exist at centimeters. If you now want to expand on that line of wondering you might ask yourself where it all ends? Is there a discrete 'point' representing a equivalent local arrow, as a 'property' more or less.
=

Actually I find it best to think of a local arrow as a property. With magnifying, aka QM, you can find other properties existing, as spin. And you can see yourself two ways, as consisting of those 'point properties', or as consisting of particles interacting. Neither seems wrong to me but depending on how you then go past that one you might want to define 'time' as something 'interacting' (particles), or not, or both. Meaning that you possibly could split the property (arrow) from what we define as 'time' when interacting/comparing.
=

Let us assume that we can translate our four dimensions into a plane (one dimension, ok, I know two dimensions) mathematically, finding a equivalence there. Then you will be 'point properties' there, or a line. No different from the way causality needs Lorentz transformations in relativity, to prove our seamless universe 'co-existing' mathematically.
« Last Edit: 02/11/2014 11:56:50 by yor_on »
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#### phyti39

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##### Re: Do we know exactly what time is?
« Reply #72 on: 03/11/2014 17:07:20 »
Depends on definitions phyti. Time is locally unchanging for each observer in my thoughts, you do not gain more life by sitting on a event horizon for example, observing a universe die. That's why we all live and die, doesn't matter where or how fast. The other comparisons is between frames of reference, and there NIST has proven time dilations to exist at centimeters. If you now want to expand on that line of wondering you might ask yourself where it all ends? Is there a discrete 'point' representing a equivalent local arrow, as a 'property' more or less.
=

All human knowledge depends on definitions, since that is all we have. We observe the world indirectly via light. Since we don't know what the patterns represent, we invent abstract concepts in their place, using our wonderful graphics oriented brain. In the process, we must remember to distinguish the concepts from what's out there, and not rely excessively on using known concepts to model new ones. Bricks are not made of smaller bricks.
Local time is constant due to effects of length contraction and time dilation.

Expressions like, "a 2 days ride", a 3 hr drive, "a half day march". are common practice throughout history to express distance and time interchangeably. The history of time keeping shows its dependence on the motion of something, with the light clock being the simplest device to directly demonstrate this.
Consider two identical clocks synchronized to the standard second. Adjust clock2 to run at half the rate of clock1. After an 8 hr workday, clock2 reads 4 hr. Was clock2 measuring time? No, and neither was clock1. The faster clock allows more precision but does not provide more "time". If the emitter-mirror distance in the light clock is halved, the frequency is doubled, and the precision improves.
Like the metronome, the clock provides the periodic "clock event" that humans use to assign to an event of interest. The historical record of events serves many purposes. The metronome provides a beat that helps musicians play music as written. The (passive) ruler which doesn't measure distance, and the clock are tools that enable a person to make measurements.
t = x/v = meter/meters/sec = sec
Time is a scalar, and has no direction, so there is no arrow of time.
Clocks just keep accumulating ticks. If we used the Chinese or Jewish calendars, we are at about 6000 yrs worth.

#### PmbPhy

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##### Re: Do we know exactly what time is?
« Reply #73 on: 03/11/2014 23:30:11 »
Quote from: phyti39
Time is a scalar, and has no direction, so there is no arrow of time.
I recommend that if you wish to delve into the physics of special relativity that you learn the mathematical terms correctly. This won't be possible unless you pick up a good textbook on special relativity that explains it using tensors. Tensor analysis is the language of relativity, and hence the math that you should learn. May I inquire as to the level of math that you're familiar with?

The term scalar as you used it comes from elementary school math and science textbooks. It that sense it means a number, real or complex. In tensor analysis it means something else, i.e. A scalar is a tensor of rank zero. This means that it's a number which remains unchanged upon a valid change of coordinates. For example; if you were working in special relativity and using Cartesian coordinates for your spatial coordinates then the coordinate transformation from one inertial frame to another, which is in standard configuration with the original one, is referred to as a Lorentz Transformation. So a Lorentz scalar is a number which remains invariant (i.e. unchanged) upon a Lorentz transformation.

I mention it so that you learn this early on. If you continue to discuss relativity with learned physicists then you'll have to learn the jargon.

#### JohnDuffield

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##### Re: Do we know exactly what time is?
« Reply #74 on: 04/11/2014 08:33:32 »
Quote from: phyti39
Time is a scalar, and has no direction, so there is no arrow of time.
I recommend that if you wish to delve into the physics of special relativity that you learn the mathematical terms correctly. This won't be possible unless you pick up a good textbook on special relativity...
The guy is right. And if you'd like to prove him wrong by pointing to the future, be my guest.
« Last Edit: 04/11/2014 09:02:49 by evan_au »

#### evan_au

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##### Re: Do we know exactly what time is?
« Reply #75 on: 04/11/2014 09:25:52 »
Slightly off-topic (sorry):
Quote from: JeffreyH
Reflection and refraction follow definite paths....  This is the concept I have a problem with. Application of the uncertainty principle should mean that this path deviates and yet it doesn't.

The design of optical telescopes takes into account of the fact that a photon which has reflected from a mirror (or been refracted by a lens) can be detected in a range of locations, making images of stars blurry.

You can constrain the amount of deviation by making the mirror larger (or the lens larger, for a refracting telescope). When building telescopes, Bigger is Better!

Deviation of photons from the "classical" laws of reflection and refraction is a fundamental part of quantum theory.

#### phyti39

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##### Re: Do we know exactly what time is?
« Reply #76 on: 04/11/2014 20:05:19 »
Quote from: phyti39
Time is a scalar, and has no direction, so there is no arrow of time.
I recommend that if you wish to delve into the physics of special relativity that you learn the mathematical terms correctly. This won't be possible unless you pick up a good textbook on special relativity that explains it using tensors. Tensor analysis is the language of relativity, and hence the math that you should learn. May I inquire as to the level of math that you're familiar with?

The term scalar as you used it comes from elementary school math and science textbooks. It that sense it means a number, real or complex. In tensor analysis it means something else, i.e. A scalar is a tensor of rank zero. This means that it's a number which remains unchanged upon a valid change of coordinates. For example; if you were working in special relativity and using Cartesian coordinates for your spatial coordinates then the coordinate transformation from one inertial frame to another, which is in standard configuration with the original one, is referred to as a Lorentz Transformation. So a Lorentz scalar is a number which remains invariant (i.e. unchanged) upon a Lorentz transformation.

I mention it so that you learn this early on. If you continue to discuss relativity with learned physicists then you'll have to learn the jargon.
Time as a derived number, distance/speed, is a variable. The Lorentz tranformation of t results in a different value for t', for relative motion.
You can do SR using algebra!
I'm not here to impress anyone, so my level of math is irrelevant.
I don't expect to discuss relativity with learned physicists on a public forum.

#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #77 on: 04/11/2014 20:09:41 »
No Phyti, you're correct in defining measures as inventions of the human mind. Without them physics won't exist. But they work and they give us the ability to predict. So they are not 'arbitrarily' made even though you can change their measures.
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#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #78 on: 04/11/2014 20:19:34 »
And Pete isn't as hard as he sounds sometimes. If you want to catch a glimpse of the math you need to read his thoughts and ponder He's a asset to us all and we should treat him as that. Just as some other guys here,  and you will see them with discussing, I think myself that we have a good blend of minds here.
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#### yor_on

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##### Re: Do we know exactly what time is?
« Reply #79 on: 04/11/2014 20:32:25 »
All in all. TNS is probably the best place i know, although I've seen some very close to it. But, we still have that glimmer of humility hiding behind our convictions, and that is in my mind, what science is about, not bullying, talking.
=

And that goes especially for you moderating.
Keep on doing the work you do.

And now I will define 'c' as something similar to a turtle, I'm positive you will agree?
« Last Edit: 04/11/2014 20:47:27 by yor_on »
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

#### PmbPhy

• Neilep Level Member
• 2784
##### Re: Do we know exactly what time is?
« Reply #80 on: 04/11/2014 22:26:51 »
Quote from: phyti39
Time as a derived number, distance/speed, is a variable.
What do you mean by a "derived number"?

Quote from: phyti39
The Lorentz tranformation of t results in a different value for t', for relative motion.
Yep. I'm well aware of that. There are two measures of time in relativity. One is called proper time and the other is called coordinate time (or simple "time"). Proper time is the time as measured on a clock which passes through the two events of concern while moving on a geodesic. The coordinate time isn't. The proper time between two events is a Lorentz invariant whereas the coordinate time between the same two events isn't.

Quote from: phyti39
You can do SR using algebra!
Yep. I'm well aware of that.

Quote from: phyti39
I'm not here to impress anyone, so my level of math is irrelevant.
I never assumed that you were. I was merely pointing out a small point on the definition of what the term "scalar" means in SR. That's all.

#### phyti39

• Jr. Member
• 45
##### Re: Do we know exactly what time is?
« Reply #81 on: 05/11/2014 19:38:49 »
All in all. TNS is probably the best place i know, although I've seen some very close to it. But, we still have that glimmer of humility hiding behind our convictions, and that is in my mind, what science is about, not bullying, talking.
=

And that goes especially for you moderating.
Keep on doing the work you do.

And now I will define 'c' as something similar to a turtle, I'm positive you will agree?

I would like to believe that the original intent of science forums was similar to that of "Scientific American", to present complex ideas in terms understandable to the common person with limited technical knowledge. Some have drifted away from that purpose. Those in their specialized fields have their own resources for staying current.

I trust your recommendation is true.