What is TIME and SPACE?

[jazzoff]

Time and space seem to be very abstract. What are they (Pls provide clear definitions, thx!)? Do they share the same basic definitions that we use in our everyday life? Why are they so important in physics? In which area are they useful?

 

How is the theory of relativity useful?

 

Questions, questions, questions.

[YT2095]

Time would be the duration between intervals of change, Space is where this change takes place.

 

is how I see it

[Severian]

At the simplest level, time and space are merely labels for categorizing events. So, if you imagine the universe as being a collection of events, then where and when it happened is just a categorization of that event, like the index of an array in computing (albeit a continuous index).

 

Then there is an additional concept of space-time distance, which provides a definition (via a metric) of the distance between two events according to some rule made up from these space-time indices. For example, the traditional 3d distance squared you are used to in the real world is (x1-x2)^2+(y1-y2)^2+(z1-z2)^2. In a 4d Minkowski flat space-time (these words just specify the definition of the rule) the distance squared is (t1-t2)^2-(x1-x2)^2-(y1-y2)^2-(z1-z2)^2.

 

GR tells us that these rules can be altered by objects.

[Daecon]

Space is the distance between things, and time is the interval between them.

 

Time and space wouldn't exist without any matter or energy to use as a point of reference for them, as the concepts of both would be meaningless.

[Davros]

There are practical applications of S/GR ....

 

A major one being the operation of certain flavours of GPS systems and the interaction between Earth orbiting clocks and Earth surface based clocks.

 

A.

Clocks on Earth run slow, compared to high geo.sync orbiting satelite, by some 45 microseconds due to GR (ie earth clock closer to the centre of the nearest large gravitational mass (centre of the Earth).

 

B.

Clocks in high geo-orbit run slow, compared to earth surface clocks, by some 5 microsends due to SR (ie the geo-sync-sat is moving fast relative to the 0 speed surface clock).

 

C.

Combining the two "slow downs" it is clear that the geo-sync-sat clock appears to run some 40 ms fast, equating to an accumulating GPS inaccuracy of some 5 miles per day.

 

Without knowledge of relativity (space/time) GPS would prove worthless within an hour, or a month, or a year (depending upon application).

 

There are other applications too, but GPS is interesting since it applies both GR and SR effects.

[michael37607]

I guess they are assumed dimensions that we have, without them, well, I can't imagine what anything would be like, I can only describe what they are in intuitive terms. Philosophers might wonder why there is time or why we have dimensional space and what they really are as you ask...and I would say...uhhh

[franz_liszt]

Newton defined absolute and relative time and space as follows:

"I. Absolute ... time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration: relative ... time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year.

II. Absolute space, in its own nature, without relation to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces; which our sense determine by its position to bodies; and which is commonly taken for immovable space; such is the dimension of a subterraneous, an aerial, or celestial space, determined by its position in respect of the earth." (principia)

So we have absolute time and space and then our measurements which are relative to absolute time and space. Time and space are the quantities we attempt to measure with instrument and are in that sense absolute. Newton also held to the absoluteness of time and space in the sense that they are unique. There is a universal time in which all events come to pass and a universal space in which all physical objects exist. Given all this there were more developments and later the aether was posited to explain how light was a wave of something.

There is a lot of metaphysical talk here, actually and Einstein's teacher Mach didn't like that. Mach was a bona fide empiricist and wanted to reduce any statement about time and space to sense perception statements and the connections between them. Since, in a positivist and verificationist epistemology, metaphysical statements are meaningless, Newton had to go. So Einstein developed his ideas with a positivist and verificationist epistemolgy in hand and a conscious rejection of metaphysics and declared the aether superfluous at best. My issue is that verificationist and positivist epistemology has been literally shot to hell in the last 50 - 60 years. Einstein got out of science at the very beginning and subjected himself to the realm of the philosophers. Well, at that time, his epistemology was OK, but now it just isn't. So why do physicists and the like continue to use a decayed epistemological basis when it comes to Einstein? Don't know. A fear of metaphysics? A nice dose of honest philosophical inquiry should help that. Maybe also a fear that science may become subject to philosophy- but it already is. Maybe fear of religious infuence. I'm a little dubious that the whole space/time issue has not gotten out of the first half of the 20th century.

[wormholeman]

For definitions on those subjects, I have always known that one word can have many definitions: It always depends on what context you use it in, if thinking in scientific terms then it will refer to scientific terms and vice/versa

 

thats my two cents

[franz_liszt]

For definitions on those subjects' date=' I have always known that one word can have many definitions: It always depends on what context you use it in, if thinking in scientific terms then it will refer to scientific terms and vice/versa

 

thats my two cents [/quote']

So what do you think of Newton's scientific definition?

[wormholeman]

franz_liszt: Newton's scientific definition? I think he stumbled upon a brilliant Idea!

I say stumbled because the apple fell on his head...:^0

[franz_liszt]

His definiton is in complete contradiction of Einstein because einstein disdained metaphysics at least when it came to "science." Einstein held to positivist epistemology and therefore, a priori rejected Newton. You seem to approve of Einstein while at the same time applauding Newton's "stumbling" effort!?? Or was all that tounge in cheek?

[wormholeman]

Tounge in cheek :^)? I may sound contridictory. But I knew nothing of metaphysics till I looked it up in the dictionary ( this day july21/2005 at precisely 5:50pm)<----now thats tounge in cheek .

[Mowgli]

Time and space are both creations of our brain. They do not exist outside our mind and experience. I know this sounds a little crazy, but compare space to sound. What is sound? Sound is an experience created by the brain based on the electrical impulses from our ears that roughly map the air pressure waves reaching them. The air pressure waves are created by vibrating bodies. While we can find some mathematical correlates to the properties of sound (eg, low frequency == boomy), the experience of sound itself is incommunicable. Sound is not a property of the falling tree or breaking glass, it is just a congitive mapping of the air pressure waves. In an exact parallel, space is a mapping of our visual inputs created by light. Now, don't you see why light enjoys such a lofty, fundamental status in our space? Its speed is a fundamental constant just because our reality is a reality created by light. But this sanctity accorded to light holds only in our space and time, our perceived reality. Special relativity (the coordinate transformation part, ie) can be thought of a description of the distortions in space and time due to the finite speed of light.

 

See http://arxiv.org/abs/physics/0507177

 

- regards,

- Mowgli

[eon_rider]

"I guess they are assumed dimensions that we have, without them, well, I can't imagine what anything would be like"

 

With out the concept of time and space life would go on. Why?

Because they are concepts that are not needed to sustain basic life.

 

However, in an advanced civilisation, we need the concepts of time and space, and especially in science to sustain a modern life.

To communicate, to serve humanity, to build the internet, to solve engineering problems, to do just about everything. Everyday concepts of time and space are very important.

 

Get rid of the concept of time and space and go try booking a table at your favourite restaurant. It would be tough to communicate your request. LOL. Even with the concept of time, it's tough to get that reservation! LOL.

 

Time and space are both creations of our brain. They do not exist outside our mind and experience. I know this sounds a little crazy, but compare space to sound. What is sound? Sound is an experience created by the brain based on the electrical impulses from our ears that roughly map the air pressure waves reaching them. The air pressure waves are created by vibrating bodies. While we can find some mathematical correlates to the properties of sound (eg, low frequency == boomy), the experience of sound itself is incommunicable. Sound is not a property of the falling tree or breaking glass, it is just a congitive mapping of the air pressure waves. In an exact parallel, space is a mapping of our visual inputs created by light

 

Interesting insight!

 

best,

 

Eon.

 

PS. I'm no expert on time. This is just my layperson, science enjoyer, opinion.

[eon_rider]

As far as standard working definitions of time you can't beat these.

 

YT2095 wrote:Time would be the duration between intervals of change, Space is where this change takes place.

 

or also "the duration between events or of an event."

 

Severian wrote: At the simplest level, time and space are merely labels for categorizing events. So, if you imagine the universe as being a collection of events, then where and when it happened is just a categorization of that event, like the index of an array in computing (albeit a continuous index).

 

Both are awsome standard working definitions of time and space, but I wonder, Mr. Severian, could one also say for time that it's

"a continuum of events?" rather than "a collection of events" or does it not matter really?

 

Just curious

 

PS. to Jazzoff http://en.wikipedia.org/wiki/Time has some cool stuff on time.