thecages

Space-time is one of those concepts that everyone knows about, but no-one really seems to know what it is. I certainly don't.

It featured prominently in a recent article in the New York Times (courtesy of that bastion of quality smut, The Sunday Times) entitled 'Black Holes Collide, and Gravity Quivers and Ripples'.

It's all about a massive installation named the Laser Interferometer Gravitational Wave Observatory (affectionately known as LIGO).
Essentially it is two sets of tunnels (each tunnel being 4 kilometers in length) that form large Vs which detect rippes in the gravitational field caused by cosmic events within 300 million light years of earth.
So what exactly do you get for $300million (capital expenditure) and $30million per annum (operational costs)?
You get a LIGO which will detect a change of less than a thousandth of a proton (not the car, the little thingie inside atoms) within the length of a tunnel.
So far (several years down the line) they've not detected anything, but everyone is holding thumbs.

Getting back to the topic at hand.
So what the fuck is space-time?

The internext offers a variety of explanations.

Firstly from the GP-B[1] site at einstein.stanford.edu.

Space-time is a four dimensional description of the universe that includes the usual three dimensions of height, width and length and a fourth dimension of time.

OK, I'm with you so far...

You might be wondering how time can be considered a dimension and why it can be lumped in with space. Consider the definition of time: time as we know it is really a man-made concept and is defined by physicists to be the measurement of a series of events. If one considers what time really is, one can see that it is simply the counting or measuring of things occurring, such as the vibrations of a quartz crystal in a watch, or the movement of the earth around the sun.
Really, time does not exist as its own entity; the event is the true variable we must consider when thinking about time. Without events occurring, there would not be a way to measure time.

sure...

Now, getting back to our space and time link, an event must occur in a space. That point in space is particular to the observer (or measurer) of the event. Therefore each point in space is associated uniquely with an event.

uhm...

Thus space and time are tied intimately together.

Wtf? How did they make that leap?

Numerous other sites offer similar explanations, inveriably featuring links to more technical explanations where, I expect, squiggly symbols will start appearing.

Heading towards amateur-ville (an area that I am certainly more familliar with) we get Cyberia.

Space has three dimensions. However, the theory of relativity predicts that time, like space, is a dimension. In order to describe a four dimensional universe which has three spatial dimensions and one time dimension the word "spacetime" was coined. Each point in spacetime is called an event.

OK

Imagine that the universe has two spatial dimensions instead of three, and that there are flat creatures living on its surface. Now imagine that the surface they are living on is subject to deformations, something like a bedsheet. The creatures living on the bedsheet can only see length and depth, they can only see within the bedsheet. They cannot even imagine the concept of height.

OK, I'm still with you. And as a matter of fact I can see how this analogy can be stretched into our three-dimensional world and how we (on a day-to-dat basis) suffer from the same myopia that prevents us from seeing the fourth dimension that shapes our world.

And finally, writer and composer Michael Spirit offers this take in a page simply entitled what_is_spaceTime.htm.

       Space-Time is the directionless flow of Consciousness
          at its most basic level within a Universe.

       It is what we call Inertia in its least compounded state.

       It is a function of the Universal Mind acting upon itself,
         generating a multiplicity of diverse thoughts within itself.

       Some of those thoughts are Life Forms, (such as we),
         who perceive undivided from within..

Hooray! I think I'll buy his beautifully illustrated tome: The Grand Uni-"Verse" of Primary Consciousness.

Grand UniVerse Presents
Some of the Most Brilliant Minds on our planet in the fields of Consciousness,
Spirituality, Quantum Theory, Quantum Reality, and Cutting Edge Theoretical Physics

       Creation!

       ...of the Illusions of Reality
         by the Mechanism of
        Foundational Existence!

       When Inertia acts upon itself,
        it generates an imbalance
         and a seeking of
       Equivalence within itself..

       As a Dynamic Function in Self Encounter, the Will of Inertia acting upon itself poses the Eternal Question;

       "What is"

       And its answer
       returns as;

       "I Am!"

[1] Gravity Probe B is the relativity gyroscope experiment being developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein's general theory of relativity.

The experiment will check, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting at 400-mile altitude directly over the poles. So free are the gyroscopes from disturbance that they will provide an almost perfect space-time reference system. They will measure how space and time are warped by the presence of the Earth, and, more profoundly, how the Earth's rotation drags space-time around with it. These effects, though small for the Earth, have far-reaching implications for the nature of matter and the structure of the Universe.