# Question about Space & Time?

by stever19
Tags: space, space-time, spacetime, time
 P: 13 I have a quick question about Space & Time. From what I understand Space and Time are interwoven into "Space-Time"- Is this understanding correct? If this understanding is correct please see my next question... With this understanding I'd assume time moves forward as the universe expands and I would think that the two are contingent on one another in order to proceed forward... so what happens if the universe suddenly starts to contract? Does time move backwards?
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 Quote by stever19 I have a quick question about Space & Time. From what I understand Space and Time are interwoven into "Space-Time"- Is this understanding correct?
Well, that depends upon what you mean by "interwoven" but yes, you can think of space and time together as "space-time" and often that simplifies computations.

 If this understanding is correct please see my next question... With this understanding I'd assume time moves forward as the universe expands and I would think that the two are contingent on one another in order to proceed forward... so what happens if the universe suddenly starts to contract? Does time move backwards?
No, they are not necessarily "contingent on one another". Right now it appears that the universe is expanding as time moves forward but that also appears to be contingent upon the amount of matter in the universe. There is no reason to think of that as a "fundamental law".
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hi stever19! welcome to pf!
 Quote by stever19 From what I understand Space and Time are interwoven into "Space-Time"- Is this understanding correct?
more or less, yes

but they're "perpendcular" rather than "interwoven"
 With this understanding I'd assume time moves forward as the universe expands and I would think that the two are contingent on one another in order to proceed forward... so what happens if the universe suddenly starts to contract? Does time move backwards?
no

it's difficult to illustrate, because we run out of dimensions

so imagine a one-dimensional universe …

we can draw that as a horizontal circle (the edge of the circle only, not the middle)

then we can draw time vertically

if the universe stays the same size, it will be drawn as a cylinder … the same size all the way up, ie for all time

if the universe continually increases in size, it will be drawn as a section of a cone, or of a paraboloid or hyperboloid, or some other shape that shows how fast it's expanding

if the universe increases size, and then starts decreasing, it will be drawn as something like an ellipse … expanding and then contracting (the size of the circular cross-section at each height is the size of the universe at the time corresponding to that height)
the time still keeps going in the same direction!

P: 13

## Question about Space & Time?

So essentially time and space are separate from one another? i.e. Time sits on top of the universe and moves forward no matter what state the universe might be in?
 PF Patron HW Helper Sci Advisor Thanks P: 25,527 yes, time is perpendicular to space, and it goes on for ever
 P: 13 Thanks guys
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 Quote by stever19 So essentially time and space are separate from one another? i.e. Time sits on top of the universe and moves forward no matter what state the universe might be in?
no no.
P: 81
 Quote by tiny-tim yes, time is perpendicular to space, and it goes on for ever
no no.
 P: 9 I would like to offer a very unscientific observation admitedly from the "arm-chair" school of theoretical physicists educated at the cosmology sction of Barnes and Noble. I understand "space-time" to be a singular concept of description. I would further acept that space and time are "interrelated" or "dependent upon one another" or "interconnected" in some manner as yet not fully understood. As such, I have never accepted the theory that "time travel" is possible and that all "time" is linear. I offer the following concepts in defense: Schroderger's Cat, the expanding universe, the acceleration of the expansion of the universe, dark energy. Schroderger posited that while all events may be possible, "reality" is created by the act of observation. The evidence that the universe is expanding and the expansion is accelerating is accepted fact. Dark energy appears now to be required to make mathmatical models of cosmology fit observational evidence. So the following example proves to me that time travel is not possible and that time is only linear: The Hubble space telescope takes a picture of the "Cat's Eye Nebula" at exactly 12:00 noon, Greenwich Mean Time. Hubble then takes the exact same picture at 12:01 Greenwich Mean Time. Are these two pictures pictures of the same thing? No. Schroderger would tell us that each picture is unique in that the "reality" of each picture was created by our act of observing each object. The expanding/accerlerating universe data tells us that the Cat's Eye Nebula was not in the same "space-time" location when the second picture was taken. As such, every mili-second of existence of this universe cannot be recreated. Essentially, every milisecond of everything we observe in our universe exists only at the time and in the state that we first observe anything, or everything in the state that we first observe the item. "Poppycock" you say. We have gone to the moon and explored space using Newtonian physics that provides exceptionally exact and replicable data. Yes that's true. However, humans have not yet achieved anything close to the level of absolute accuracty that "time" as we know it represents. Thus, all of our activities in space can be reduced to the old government standard of "close enough is good enough." Here's a simple experiment: Look at a clock with a second hand. Concentrate on the movement of the second hand. Watch each second move. That is our standard of reality. Even as blazingly fast as our brain thoughts are, one cannot even think of more than a few things in the interval of a second. Try it. Now in reference to the emmense exactitude of "time", the passage of one second is an incredible large interval - maybe a comparison akin to an atomic bomb blast compared to a two inch firecracker. Now assuming that "space-time" is a singluar unit that measures "something" in existence in this universe, consider how likely it would be to arrive at a point in space billions and billions of light years away from earth at exactly a pre-identified second? Not only could such "temperal" accuracy never be achieved, the "location" of which you desired is never in the same place in the universe. Yes, I understand that concepts such as "M theory", "strings" "multi-verse" "brain" "11 dimensions" all suggest wildly exotic ideas as to how the universe operates and that in such exotic environments, "anything" is possible including the non-lineality of time. But here is a thought, humans are linear, temporal entities. As a committed Christian, I believe that there are realities beyond our ability to conceive or understand while we occupy a living human body. As such, I do not believe that time travel is possible for humans or that non-linear time is a concept that is a possiblity for us. jim coster, pittsburgh, pa

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