If time is a dimension, how far away is the past? In meters?

Factual Questions
1

For example, say you had a light that blinked every second. If you could observe two blinks as they moved through the time dimension, it seems you could observe some distance between those events. What is that distance?

Like, if you were standing at a river and dropped corks into the water once a second, you could measure the distance between corks (in meters) as they flowed down the river. Can you do the same thing if the river was time?

Or is it a nonsensical question to think about how many meters away something is in the time dimension?

2

Time is a dimension in that it is something that can be measured; it is not (under normal conditions) a spatial/geometric dimension; calling it the fourth dinesion often misleads people into thinking that it means A fourth dimension like the other three.

3

300,000,000 m/sec

4

According to my back of the envelop calculation I believe it would be 1.4x10[sup]26[/sup] meters.

5

Staff Report on How many dimensions are there and what are they?

6

Regardless of whether time is a dimension, it’s measured in seconds, days, etc. You can no more measure time in meters than you can measure your height in quarts.

Your specific questions have to do with combination measurements. Given certain data (e.g. the river flows at x mph), one can correlate the various measurements. Thus you could say that a cork would be y feet downstream after z seconds. But that measurement in feet is not a measure of the time involved, it just corresponds to the time involved, which is still measured in seconds.

7

About 1.6 x 10[sup]-35[/sup] m.

8

Perhaps the OP was thinking along these lines though - "What would happen if I took a particular piece of spacetime and * rotated* it such that objects (events actually) along the time dimension rotated into one of the spatial dimensions. How “long” would a second look? My guess is 300,000km.

9

The dimension of time is measured in units of time (minutes, seconds, etc.), as the dimensions of distance are measured in units of distance (meters, etc.).

10

My original question was based, it sounds like, on a misunderstanding I had that we are moving through the time dimension like we move through the other three dimensions. It sounds like you cannot measure the distance between two points in time as if they were actual points in 4 dimensional space.

Although several people have given numbers as to what they think the distance would be, I’m not sure if those guesses or based on some calculation.

11

The numbers are based on the symmetry caused by setting the constant c (the speed of light) to equal 1 and varying the time measuring factor to achieve this. Though this leads to an answer to your question from
c(in m/s) meters = 1 second
This is only valid in a mathematical construct, it is not clear that time can be reasonably measured in terms of distance, nor that distance can be reasonably measured in terms of time. The symetry is however attractive (it makes calculations easier) and may well have merrit. Though other calculational symmetries can lead to time being an imaginary value when measured in terms of distance, giving
1 sec approx= i 300,000,000 meters

where i = sqrt(-1)

[B}Terminus Est** mentions 1.6 x 10[sup]-35[/sup]m this is the value of Plank Distance, which is the smallest meaningful measure of distance, this is related to the smallest meaningful measure of time by the same factor of c.

Cheers, Bippy

12

I believe that it’s physically meaningless to say the speed of light = 1. That is, it’s an untestable hypothesis. However, scientists make this assumption all the time. Relativity, especially things like Lorentz boosts, makes a lot more mathematical sense if you do it like that. Certainly, if you were going to set the speed of light to a unitless number, the only number that makes sense is 1.

And so, if you ask a scientist how big a second is in meters, the only reasonable answer is 299,792,458 m, even though this isn’t a number you can measure in a particular experiment.

13

elfoldo: You can, and no doubt do, measure distance on the time dimension. You do this all the time. You are moving along the time axis of the four-dimensional set of space-time. The way you measure that progress is in units applicable to that one axis: seconds, minutes, hours, days, weeks, months, years, etc.

14

Some items you can use to compare.

Distance from end of the universe to the other end might be compaired to time from beginning to end.

Smallest unit of distance is plank lenght

Smallest unit of time is plank time.

Something moving one plank lenght in on plank time unit is moving at c.

15

Erm, I think that calling planck units the “smallest” units is misleading. They’re the scale at which quantum gravity is supposed to be manifest, and thereby the scale at which our current physics is not totally useful.

I could be wrong, but I don’t think this is the same as being the smallest units in any meaningful way.

16

When dealing with relativity It’s very common for time to be measured in meters i.e. one meter of time is the time it would take for light to travel one meter.

However this does not in anyway imply that time is a fourth spatial dimension, in fact it most assuredly is not. Three-dimensional space cannot curve into a fourth dimension of time.

If you measure distance in lightyears and time in years then c = 1 (this is also true for other choices of units), If c could not be set equal to one then a lightlike worldline would not be a 45 degree line in the lightcone.

17

Achernar, it’s not an untestable hypothesis to say c = 1, it’s just a definition of a particular system of units, and of course you can use any system of units you wish (as long as they’re consistent), because units are utterly arbitrary constructs.

It is, admittedly, a little strange to give time the same units as distance. But I don’t see there being an a priori reason that we must give distance and time different units, except that it’s awfully convenient to do so because distance and time aren’t the same thing.

That said, I guess I would claim that you oughtn’t to say that two things are separated in time by X meters because meters are a unit associated only with distance. You can say that the separation in the time-like dimension is X meters, however, in which case the conversion factor would be c.

18

You’re right. I misspoke. When I said “an untestable hypothesis” I meant “not a testable hypothesis”.

I agree that you shouldn’t talk about time being measured in meters, unless you’re in third-year undergrad physics or above. From that point on, it’s the most natural thing in the world.

19

In or around 1974 an American physicist named Frank Tipler wrote that, based on what is understood about the relationship between time and the spacial dimensions, there was a method–in theory at least–for constructing a time machine.

Tipler said that if one constructed a cylinder out of the “stuff” of which black holes are constructed, and spun it very fast, the material would not collapse in on itself and form a singularity. Some physicists dispute this. Tipler also thought that one would not be crushed by entering the space in the center of the cylinder; I guess this would work on the same principal as the idea that a person at the center of the earth should be weightless as the mass–and, therefore, the gravitational pull–acting on him or her would be equal on all sides.

In any case, Tipler said that if such a whirling cylinder was constructed and the device spun at sufficient speed, it would contort or “tip” the four dimensional geomerty of the space which it occupied. (I am probably not explaining this very well, but then, I’m not a physicist.)

Suppose you take an ordinary cube and draw arrows along its sides, marking some as “height”, others as “length”, and others as “width”. If you then tip the cube on its side, two of the dimensions “switch places”; for instance, the arrow which is being “height” may now be pointing in the direction in which the “length” arrow was pointing a moment before.

In a somewhat analogous fashion, in Tipler’s model, time would “switch places” with one of the three spacial dimensions. This would mean that if one moved forward or backward inside the cylinder, it would mean you were moving through time. Once the cylinder stopped spinning and the four dimensions were restored to their normal orientation, the person who had moved about inside the cylinder would find he or she had moved forward or backward in time.

Which direction in the cylinder would be the future, and which would be the past? In H.G. Well’s novel The Time Machine the anonymous inventer says that he can make the parts of his machine rotate in either of two directions, but he won’t know which way pushes the machine forward in time and which pushes it backwards until he actually tries it out. It would seem to be the same for Tipler’s hypothetical time machine.

I have read that one limitation on the Tipler design is that it could not put a person farther into the past than when the cylinder was first built. This has to do with the idea that the cylinder itself does not travel in time except in the ordinary sense that everything and everybody “go” from their past existence to their future through the eternal present.

To address the question in the original OP, how would distance within the cylinder relate to time? Would moving one foot forward move a person a second ahead in the future, or a month, or a thousand years? Until the device is actually built and tested, no one seems to know.

` within the device relate

20

Wow All that space doubled the lenght of the post.

THe theory I heard is that you somehow enlarge a wormhole which are currently everywhere in space-time by using negitive energy (or negitive mass - I guess this would be the same thing E=mc^2). Once you enlarge the wormhole to a usable size you can spin one end (or just move very fast) while the other end stays still.

As one end moves (it helps if you can get it to near c) due to relitivistic effects it moves through time differently then the stationary end. This difference means that one end is timeshifted with respect to the other. Enter one end and you will appear at a future time going one way and a past time going the other. For some reason maybe only the going into the future works.