Sunday, July 11, 2010

Food for Thought: The chicken-or-egg problem with time-or-speed

How do you define time? Well, time=distance/speed. Very good. Bravo. But hang on a second. How do you define speed. Speed=distance/time. Does it not constitute a circularity of logic?


cool head leader said...

I simply cannot get what is wrong with the equations? Mimi do not try to play smart what you are not.

Anonymous said...

First measure time and then velocity.

Anonymous said...

Mimi, better stick to Hindu-bashing and calling Pakistan miserable. Science is not your forte, and you are only making a fool of yourself.

Nobody "defines" time as distance/speed. Nobody except you. Time is a dimension of the space-time continuum. Speed is indeed defined as distance travelled/time taken.

Speed = (distance travelled)/(time taken) -------(1)
Now divide both sides by Speed and multiply by (time taken) and you get the equation
Time taken = distance travelled/Speed. ----------(2)

As you may have noticed, the equations (1) and (2) are one and the same equation (an equation does not change by multiplying or dividing by same quantities on both sides), and there is no "circularity of logic" involved here. Oh, and also, the quantity in the equation is "time taken" to travel a certain distance, and not "time" in general.


Whatever said...

Hey, I thought this is where you vent your anger, frustration, disgust and hysterics - add "idiocy" to that list to make the heading more descriptive.
Here's the thing - as long as you, due to your daddy issues, are abusing Indians, Bengalis, Hindus (and opportunistically also the americans) you can come off unscathed in an argument because you can twist the truth in whatever way you want and also ignore the facts others are presenting. However, when you get to the realm of science where most things have precise definitions, you can't just hand-wave or wish away the facts. So as others are advising stay away from that or else you will get bbq-d.
There is no definition of time, you can define a measurement of time - which is what JS is saying. e.g the SI unit of time i.e. seconds is the time taken for a fixed no of radiation cycles when, I think, a caesium atom transitions between two energy states. Don't try to imagine that you are finding some assbusting logic here by talking about something that you learnt in high-school (ohh wait, since you are so omniscient, may be you just knew about it). The concept of velocity (or loosely speed) is derived from the concept of time and no-one has EVER tried to define time using speed. So no circular logic here .. just a dearth of the same at your end.

Mimi Sen said...


Today as we are discussing science, I shall stay away from the secret story of your birth. I have no mood to elaborate on how you were born out of a gang rape, your dear mother was a victim of; marks are still there on your mother’s hips as the telltale sign of that incident. Remember “Hips don’t lie”.

Coming back to science, it’s been a long time that I did not laugh so much as I did on reading your two statements: Statement 1. “when you get to the realm of science where most things have precise definitions”, and, Statement 2. “Time has no definition”.
Now, Mr./Ms. Whatever, or, in general, whosoever reads this weblog, please make a note that this weblog is not meant for the pedants. If you are looking for bookish knowledge or are willing to show your mugged-up wisdom that you have learned from your dubious father(s) or want to display your superficial street-smartness to woo a high-heel thong-clad woman, this is not your place. You will just find your ass burned in thousand flames here, I dare you.

Time, as dealt with by Physics, is one of the most enigmatic quantities in the whole Universe, even more enigmatic than the antimatter or dark matter. It is virtually impossible to define a unit time without the help of some other quantity, more precisely velocity; indeed a unit time cannot be defined without assuming or defining the velocity of some object (in practice that object is either photon, or electron or many other subatomic particles that travel at the speed of light). Funnily, as the velocity increases the time also slows down (a fact known as time dilation found in the most amazing discovery in science, namely the special theory of relativity by a clerk in a patent office). It is not difficult to find a book or internet site which explains how a unit time is measured. There is no big deal in such bookish knowledge. But it would be stupendously mystifying to think what happens to the quantity time if the spin of a caesium electron slows down. Does it imply that the unit time is slowed down too? Indeed it slows down the time. However, we now know that the radiation of cesium, like the speed of light is constant in any frame of reference, thanks to the special theory of relativity. So there is almost no chance of slowing down or speeding up of cesium radiation in a particular frame of reference. I say ‘almost’, because the constancy of speed of light is just an assumption supported by numerous cosmological experiments. Consequently, a unit time is different in different frames of reference moving at some speed relative to each other. This shows exactly why it is impossible to define time without defining the velocity of some object. Now, curiously, when you compute the velocity of some other objects, say the velocity of a spacecraft, you invoke a quantity called unit time which is actually computed from the velocity of a photon or such like things. I can’t explain more. If I want to describe it through a directed graph, it would look like this: (1) assume velocity of a particular object (e.g. electron spin of caesium atom)(2)Fix unit time(3) Compute velocities of other objects. It takes time to feel the mysticism of the special theory of relativity and, as a result, the relativistic nature of time. Ask your favorite professor at NASA or Harvard to explain that in more detail.

Mimi Sen said...

Understand your bottomless ignorance and try to feel elated by the above explanation that I gave. First of all, the equations you wrote make no sense with respect to the question I posed. Nonetheless, FYI you can only divide the both sides of an equation by a nonzero quantity and there is no guarantee that it is the case in your explanation. It seems that your scientific knowledge is just limited to boning up various terms like space-time continuum, energy levels of caesium atom etc. without any understanding of the related phenomena (This comment applies to your new-found patron Whatever too). So hope you guys are now wiser than before on the subject of the most mysterious physical quantity called time.

@anonymous: Hope now you know the question and the answer too. It takes intelligence to understand the question too.

@CHL: chill man. To understand nature is to have the pleasure similar to orgasm. But
keep a cool head. You should know what I mean.

chamatkar said...

erom khistibaz meye ami khub kom dekhechi... shows the american culture...

Anonymous said...

Darling, make it a point not to read things that are beyond you. The result is NOT pretty as your bottomless comment shows. Your foolish proposition being exposed, you are now desperately clutching at mysticism - the same thing that you said you hate and accused Ray of indulging into. Mysterious and enigmatic indeed. Tell me, what quantity can you define without using any other quantity as reference?

But let it be, I won't argue with you... no use arguing with someone who has forgotten school level physics and maths and is chasing cesium atoms. By the way, it felt nice to know that electrons travel at the velocity of light. Never too late to learn.

Anyway, keep reading books. Someday you may actually understand the stuff.

Anonymous said...

The above comment was by me. - JS

Anonymous said...


A unit of time is never defined with respect to a velocity! That would be completely meaningless. Velocity with respect to what? A "universal" reference frame? That is precisely the point of Einstein's special theory of relativity - there is no "special" universal frame of reference that is true for all observers.

So even though the times measured in 2 different (inertial) frames are different, they can be related to each other via Lorentz transformations. So there is no problem or paradox there.

Actually, in the modern paradigm of spacetime (based on Einstein's General theory of relativity), it does not matter what units you measure time or distance (and hence velocity) in. Any set of units is fine, since what really matters is something called the "invariant interval" or in physics jargon "metric". If spacetime is flat (that would be in the absence of strong gravitational fields) the metric is given by

ds^2= dt^2-(dx^2+dy^2+dz^2)

where dt, dx, dy, dz etc are infinitesimal displacements in the time and spatial directions respectively. This quantity is absolutely crucial since it is constant regardless of the reference frame you measure it in (and regardless of what your units of time and distance are).

In the presence of gravitational fields, the metric looks very different. For example in the presence of a massive object (like a neutron star or a black hole) the huge gravitational field warps spacetime and the metric it looks like

ds^2=A(r)dt^2-B(r)dr^2- C(r,t) d Omega^2

where I'm using polar coordinates (r,Omega) and A,B are functions of these.

Anonymous said...

@Anon above :

Keno je likhte geli ... eto ese abar khisti marbe.

Mimi Sen said...

Before I go into further discussion, I assume a lot of people who visit my weblog may not be familiar with the wonderful phenomenon called time dilation. They may like to watch the following video for that.



I agree with what you said. Times measured in two different reference frames are related by the Lorentz transformation as you mentioned.
My question here is different altogether. I’m NOT interested in times in different frames of reference and how they are related. Therefore, for the moment, it is probably not very necessary to bring in heavy neutron stars or super-massive black holes into the scenario, and how Lorentz transform is affected by that. Let first thing come first. What I want to know now is: How shall we measure a unit time, say 1 second, with respect to a particular frame of reference, say an inertial frame of reference? In other words, is there any physical method that can measure the one-second time interval without implicitly assuming the velocity of some objects? I think no. Tell me one such method that determines one second. I shall show you how such method implicitly assumes the velocity of some object before measuring the unit time. An example: the time taken by a photon particle to travel 186,000 miles is known as one second. Now, see we have already fixed the velocity of photon as 186,000 miles/sec before actually determining the length of one second. I claim that no matter what the method is, be it electron-based or gamma-ray-based or whatever, I shall be able to establish that the speed of some object is actually assumed or fixed a priori, to measure the unit time.
It is no big deal that the unit of a physical quantity is derived from the units of other quantities. The interesting part is an apparent paradox in the above problem: unit velocity is derived from time and unit time is derived from velocity.

Mimi Sen said...

The link

Anonymous said...


The only reason I mentioned neutron stars and black holes was to give you an example of the metric, which is the important thing in doing calculations in physics. They are indeed beside the point in this discussion.

Getting back to what you replied, the standard definition of a second is (according to Wikipedia)

"The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."

How does that relate to a velocity?

Anonymous said...

Here's another one for you:

Suppose the unit of time is defined as the inverse of the decay constant of Plutonium.

Explain to me how that is related to speed.

Anonymous said...

Here's another one for you. Suppose the unit of time is defined as follows (purely in terms of 4 well-known physical constants):


hbar=reduced Planck's constant
G=Gravitational constant
mu_0=permittivity of vacuum
epsilon_0=permeability of vacuum.

You can check, or have someone at your intellectual level like a researcher at NASA or a professor at Harvard (actually a high school physics kid would suffice) explain to you that the above combination has the dimensions of time.

Explain to me how the above, 100% correct, formulation of a time unit involves a speed.

AnonymousToo said...

Mimi's on a sabbatical. She is gathering more expletives for us. We should all get ready to be served with the choicest adjectives about our mothers and then bow down in awe as she unravels the mysteries of the universe, the conspiracies of the bengali, the hindu, the indian, the israelite , sonam kapoor and greatbong.

Anonymous said...

Mimi is lying low (literally) after being gang banged by pigs who mistook her as one of their own.

Fuck_Mimi said...

What's the time taken to gang rape Mimi??

Anonymous said...

So raping Mimi not completed yet??