# Most basic description of what time actually is

I thought about the most basic description of what time acually is and came up with this.
Time is the distace between two points in space.
im not a person who reads alot of physic books so I don't know alot about the subject. Do you agree or disagree?

## Answers and Replies

mathman
Science Advisor
Length is the distance between two points on space. Time is how long it takes to get from one point to the other.

Sometimes the obvious happens to be true.

how did you come up with this? i disagree i believe time is not real but a construct of the human mind because in your theory different speeds of travel wuld cause different times so it cant be true.

let me rephrase it
time is the space between two points in space.

jcsd
Science Advisor
Gold Member
You can find the distance ($ds$) between two points in n-dimensionsal (Euclidian) space from:

$$ds^2 = {x_1}^2 + {x_2}^2 + {x_3}^2 .... + {x_{n-1}}^2 + {x_n}^2$$

which in our three dimensional world is:

$$ds^2 = x^2 + y^2 + z^2$$

notice no need for any time dimension to find the distance between two objects in space.

time

Is there an exact measurment for time?

Originally posted by jcsd
You can find the distance ($ds$) between two points in n-dimensionsal (Euclidian) space from:

$$ds^2 = {x_1}^2 + {x_2}^2 + {x_3}^2 .... + {x_{n-1}}^2 + {x_n}^2$$

which in our three dimensional world is:

$$ds^2 = x^2 + y^2 + z^2$$

notice no need for any time dimension to find the distance between two objects in space.

The fourth coordinate is ict. This might be important in a thread called time.

jcsd
Science Advisor
Gold Member
No, we're talking about seperation in space not spacetime, space tiome has the metric (depending on the formalism you prefer):

$$ds^2 = (x^1)^2 + (x^2)^2 + (x^3)^2 - (x^4)^2$$

Where $x^4 = ct$.

jcsd
Science Advisor
Gold Member
Unless of course your talking about Euclidian quantum gravity which does form a four-dimensional locally Euclidan space with one dimension equivalent to -ict.

what is the basic concept of spacetime?

does it relate in that time does not exist without space and space with out time.

with out two points in time does space exist?

jcsd
Science Advisor
Gold Member
mikelus:

Above I gave the equation for finding the distance between two points in (Euclidian, i.e. flat) space (if we take one of the points as the origin):

$$ds^2 = x ^2 + y^2 + z^2$$

In relativity there are a group of equations which show us how differnt observers travelling at different speeds view time and space:

$$x' = \gamma(x - ut)$$
$$y' = y$$
$$z' = z$$
$$t' = \gamma(t - \frac{ux}{c^2})$$

Where the primed dimensions (e.g. $x'$) is how an observer travelling along the x axis with speed $u$ views these dimesions compared to how an observer in this rest frame views them. $\gamma$ is equal to $(1 - u^2/c^2)^{1/2}$

If we apply these transformations to the first equation, we find:

$$d(s')^2 = \gamma^2(x - ut)^2 + y^2 + z^2$$

this means that $ds^2 = d(s')^2$ if and only if $u = 0$. So observers travelling at different speeds will not agree on the distance between two objects in space.

If we look at the metric for (flat) spacetime given in my first post in a simlair way we see it is of the form:

$$ds^2 = x^2 + y^2 + z^2 - c^2t^2$$

And we as in the metric for space we perform the same opertaion for an obnserver travelling at a different speed (i.e. perform a Lorentz tarnformation) we get the equation:

$$d(s')^2 = \gamma^2(x - ut)^2 + y^2 + z^2 - c^2\gamma^2(t - \frac{ux}{c^2})^2$$

if we expand this out we get:

$$d(s')^2 = \frac{x^2 - 2utx + u^2t^2}{1 - \frac{u^2}{c^2}} + y^2 + z^2 - \frac{c^2t^2 - 2utx + \frac{u^2x^2}{c^2}}{1 - \frac{u^2}{c^2}}$$

if we factorise and divide we find:

$$d(s')^2 = x^2 + y^2 + z^2 - c^2t^2 = ds^2$$

So we should say that two observers will always agree on the distance between two points in (flat) spacetime, even if they are travelling at different speeds. This is why the concept of spacetime is so useful as we use it to find equations valid for all observers not for just one particular observer.

You may of also noticed that the Lorentz transfomration is very simalir to rotating something in space, in this way we can think of velocity as a rotation in spacetime.

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HeavensWarFire
You should all read my post.

Time doesnt exist, in the way you think a Chair exists. Time is a an abstract concept that relates to change.

HeavensWarFire
You failed to prove yur explanation of absolute time

Above I gave the equation for finding the distance between two points in (Euclidian, i.e. flat) space (if we take one of the points as the origin):

You seem to confuse absolute spead measure, with absolute time measure. The question is not about the actual distance between 2 points, but rather, what is in fact the smallest unit of time measurable.

Heres why i think yur formula doesnt work: you fail to take into consideration the idea of infinite divisability. You take a foot, and you dived that in half. Take this half, and divide that in half. Repeat this process of diving each, and every successive half, and you will never find a terminating point. Hence, your math formula for distance is only contextual, and it does not answer any of the paradoxes of Zenos.

To define an absolute unit of time, you need to first define an absolute unit of distance that you can not mathetimatically subdivided, and you need an absolute unit of speed. Once you answer these issues, then maybe you can come up with an actual unit of time that can not be further subdivided into smaller units.

HeavensWarFire
Hello

Knock, knock:
with out two points in time does space exist?

Space is simply the absence of "matter." without matter, you could never have an atomic notion of a void.

Secondly, time seems to only come into consciousness when you start to think about distance, and speed.

But over, and beyond that, theres no such thing as time. Mathetimatically, you an infinitely add, or subdivide, hence theres not absolute measure of any kind in the truest sense.

jcsd
Science Advisor
Gold Member

Originally posted by HeavensWarFire

You seem to confuse absolute spead measure, with absolute time measure. The question is not about the actual distance between 2 points, but rather, what is in fact the smallest unit of time measurable.

Heres why i think yur formula doesnt work: you fail to take into consideration the idea of infinite divisability. You take a foot, and you dived that in half. Take this half, and divide that in half. Repeat this process of diving each, and every successive half, and you will never find a terminating point. Hence, your math formula for distance is only contextual, and it does not answer any of the paradoxes of Zenos.

To define an absolute unit of time, you need to first define an absolute unit of distance that you can not mathetimatically subdivided, and you need an absolute unit of speed. Once you answer these issues, then maybe you can come up with an actual unit of time that can not be further subdivided into smaller units.

They're not my formulas they're Pythagoras's, Lorentz's and Minowski's, they lie at the heart of special relativity.

I'd also like to tell you taht ds, x, y, z and ct do not take discrete values (this should be rather obvious as there are only a few cases where they can all take on non-zero but discrete values).

I'm not confused, all I was doing was explaining the well-known concept of space-time, It appears YOU are confused.

HeavensWarFire
Try reading first

How nice of you to ignore the main crux of my thoughts.

To define an absolute unit of time, you need to first define an absolute unit of distance that you can not mathetimatically subdivided, and you need an absolute unit of speed. Once you answer these issues, then maybe you can come up with an actual unit of time that can not be further subdivided into smaller units.

Ok,wise guy, tell me, how much time has there been since the creation of all life? And how much time will there be there once all is killed off in what is called entropy? Surely you know, for you have many theories in your head.

Perhaps you do not understand the idea of "infinite divisability"? Tell, what is the smallest unit of measure that you can think of? Surely you know? Did you not know that mathematically speaking, many things are endless? A foriegn concept to you is it? And perhaps you are equally confused with what is called a Paradox?

x=length
y=width
z=depth

This is just the standard variables for the dimensions of the space, object, continuum, it doesnt tell me anything about what is the smallest unit imaginable of anything, whether we are speaking of distance, time, or speed.

jcsd
Science Advisor
Gold Member
No, you don't understand, where did I say that the temporal and spatial dimensions weren't continuous? Infact if you look at the formula:

$$ds^2 = x^2 + y^2 + z^2 - c^2t^2$$

You find there are very few values you can put in that would allow ds, x, y, z and ct to be discrete, off the top of my head I can only think of 1 set of values (and therefore mutiples of these values) that allow them all to be natural numbers: ds = 3, ct = 3 and where x y and z take the values 1, 1 and 4 (that's of course not to say there aren't more), the point is you can't make the formula discrete without excluding a whole set of solutions.

Now stop blathering.

HeavensWarFire
lol

Ahahahahahahahahah...........

Now stop blathering.

Alright man, i will speak at your level: a formula for how you may go about in solving a certain equation is not the same as the demonstration.

Your formula is cute, but, you still havent furnished me with an actual answer to the question of whether or not, mathematically you can actually arrive at the smallest unit possible. And until you do that, your above means nothing to me. Theory, and practise are not of the same realm. So tell me in what way your formula is of any significance? What can you solve with your theory exactly?

jcsd
Science Advisor
Gold Member
1) this is not my thewory and I never mad such a claim, it was a brief introduction to the concept of spacetime a key part of Einstein's theory of relativity. Relativyt is a key part of modern physics it's applications are num,erous and it has been tested many times.

2) I did not make any comment on whether time is discrete or continuous, infact relativity does tactitly assume that time is continuous, so why do you keep on going on about the infinite divisbilty of time?

minimum time

Regarding your questions about minimum time and space, here's a paper I wrote recently. Don't know if it makes sense but it addresses those issues exactly. I'm pasting it from my thread from the Strings forum. It probably belongs in theory development anyway.

The Minimum Time

By Edsel Salvana, MD

String theory has generated a minimum size in terms of
physical distance. Planck length is the smallest
possible distance and is purported to be the size of a
string. However, there has been no postulated minimum
time. Since time itself is a dimension, the question
arises as to whether there is a minimum amount of time
beyond which the string becomes undefined.

To tackle this problem, we return to the definition of
matter in light of the string theory. In essence,
matter (and energy, for that matter) is merely a
manifestation of the vibrations of a string as
modified by a Calabi-Yau space. Yet a vibrating object
has a period during which it makes a complete
vibration. If the characteristics of matter are
inherent in the vibration pattern, then the period in
which one vibration is manifested determines the
character of that matter and no less.

As an example, we look at light. Light is made up of
photons. A photon is a string with a distinct
vibration pattern. The speed of light is 300,000 km/s.
The time in which light traverses the Planck distance
is the Planck time. Yet a photon can only fit in a
space no smaller than a Planck distance since it
itself is a string. By that virtue, the photon is
actually taking up the whole of the Planck space. It
cannot be halfway in, or halfway out or any proportion
thereof precisely because it cannot otherwise be
defined as a string (it cannot be half a photon) and
there is no smaller space. Furthermore, the
characteristics of the photon cannot be manifested
without a complete vibration. By this reasoning, the
time it takes a string to produce a photon cannot be
less than the Planck time because the vibration would
not be complete. Taken in another way, you cannot have
a complete vibration if you do not have a complete
string.

Using this analogy, if at the time of the Big Bang
(zero time), photons were produced, they would have a
period of Planck time at least. That is why all
photons travel at the speed of light (not faster or
slower). There is no “in between” state because the
vibration necessary to generate a photon would not be
complete. Precisely because of this point, all photons
in the universe should be “in synch” with each other
in multiples of minimum (Planck) time.

Whether other particles are subject to this “minimum
time” is self-evident since all particles are made up
of strings. The question is whether certain particles
have a larger “minimum time” because it takes longer
for the string to generate a complete vibration. I do
not think this has to be the case since the minimum
requirement for one vibration would be one complete
string. Nevertheless, if some particles (especially
those slower than light) have a longer minimum time
(the time it spends generating one complete vibration
in a Planck space), these should be greater than (they
are multiples of, since there is no smaller unit by
definition) Planck time since nothing can travel
faster than light and each vibration requires a
complete string.

An interesting consequence of these arguments is that
matter and energy is being “created” in multiples of
“minimum” (Planck) time. With each vibration, a string
generates the same particle over and over again over
time. When a string’s vibration is changed, then the
type of matter (or energy particle) it manifests is
changed. Whether the time to generate the properties
of the matter or energy particle remains the same
(Planck time or multiples thereof) remains to be seen.

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