Expert: Jayendra Upadhye - 8/6/2008

Question
QUESTION: Please explain to me why and how space and time are the same thing. Keep in mind that I'm an idiot. Thanks, Joe.

ANSWER: Hi,

I take it by "idiot" you mean "lay person" / "beginner" / "simpleton" etc from the viewpoint of an "expert".

Well, since i can't claim to be an astrophysicist, i am not an "expert".

Acknowledging that, i can then move on comfortably to address your question and explain my POV in as simple terms as possible.

I have often come across many questioners on this site, who "have something up their sleeve so to say, or an axe to grind, or someone they want to "bite the dust" etc...they often start off as you have, and when one has answered, come back viciously with "you xxxx! And you think you are an expert!! Here ..take this lousy rating"...and end up rating one with 1,1,1,0 etc ..

All one can do is pity such individuals. Period.

Coming to your question, (link:- http://en.wikipedia.org/wiki/Space-time_continuum...and no, i dont know neither do i understand the abstruse mathematics involved), all one can say is :-

1 - Take euclidiean geometry, or say cartesian co-ordinate system of
   3 dimensions.
   We say the enity called "space" has 3 dimensions, but yet cannot
   say "length" is actually "width" and also the same as "hieght",
   when we know we are describing these 3 as 3 separate axial
   aspects of ONE entiry we call SPACE.

2 - Likewise, in 4d space-time entity, we are actually using a higher
   version of THAT verisame enity, and now describing a 4th
   dimensional aspect of it.  

In both cases above, TIME (excluded in 1st or neglected) is BUT ONE co-ordinate axis, 1 of 4 now, of a SINGLE ENTITY we call space-time continuum. Only in that sense, space and time are the same.
Rather like saying..length,breadth,depth PART OF single entity in cartesian 3d space, and TIME is also a part in 4d calculations.

It is all how one describes things.
Often it is convinient to use "only a facet or aspect" of an entity in a particular context.
For example:- we never discuss "width or length of the atmosphere" do we? we only discuss its depth! because the other 2 aspects are meaningles in a spherical entity.

Likewise, in relativistic scenarios, when lorentz contraction etc are distorting physical dimensions due to altered TIME perceptions, it is USEFUL to discuss the ENTITY we NORMALLY call SPACE, as a SPACE-TIME entity.

Only in these senses, space and time are one (or separate).

In lay terms, though "newyork is two hours away" does convey distance provided we know the speed, to do science, it would be meaningless as it lacks a directional information! Then we WOULD need co-ordinates of displacement NOT time!! In THIS sense time is part of the system and separate from it too.

Hope that suffices.
regards
Jayen

---------- FOLLOW-UP ----------

QUESTION: I have nothing up my sleeve, infact, i don't even have sleeves! I live in Key West Fl. I read your answer and, being an idiot, did't understand it much. Am I looking too deep or is it that the distance one travels in space measured by time and not distance? I'll never understand how a person doesn't age at the same rate when traveling at or near the speed of light, either. I really need things broken down to the atom in order to understand them.

Answer
My God!
That's a very tall order indeed!
Joe, i wonder if i am upto the task.

1 - In stellar terms, "as the crow flies" gets right, because the "crow"s (light's) speed is invariant (at least so far) at 300,000 km/sec.

So the farther back one looks, well, light started that much far back in time in order to cross that distance and reach you (so you could see it). Which also means you are seing it as IT WAS that many years ago, and the damned thing actually changed without you knowing it, in the mean time. THAT change info will reach you even more late, in order of succession.

That is what one means when one says one looks back in time when one looks deep into space. Since light velocity is KNOWN, we can use the "crow flying" term of LIGHT YEAR, where we describe distance travelled in one year by light, as 1 light year. It is a FIGURATIVE term. Not a literal term.

Regarding differential ageing..well you will have to cross that bridge yourself, by reading and "internalising".

regards
Jayen