# Speed of time?

1. Jun 20, 2009

### monty37

what is the speed of time?

2. Jun 20, 2009

### Hootenanny

Staff Emeritus
Perhaps you could elaborate on your question?

3. Jun 20, 2009

### Naty1

Time appears to pass at a constant rate and that was a cornerstone of Newton's theories. But Einstein showed that space and time are NOT fixed and immutable; they vary according to one's relative motion....space contracts and time slows as relative speed between observers increases. Identical events are observed to occur at different times in different frames. Time also slows down near massive gravitational bodies where gravitational potential is greater.

Check Wikipedia at http://en.wikipedia.org/wiki/Time#Modern_physics

for some additional description and further references.

Last edited: Jun 20, 2009
4. Jun 20, 2009

### Staff: Mentor

Time is the thing measured by an ideal clock, and an ideal clock ticks at a rate of 1 second/light-second.

5. Jun 20, 2009

### Max™

What is the speed of Left?

6. Jun 20, 2009

### negitron

More accurately reflecting the OP: what is the speed of height? If you consider time as a dimension, it doesn't move at all; instead, objects move through the time dimension in the same way that they can move through the spatial dimensions.

7. Jun 20, 2009

### fluidistic

According to wikipedia
. I think we all agree on any similar definitions.
Hence the question
has no sense.

8. Jun 20, 2009

### HallsofIvy

One second per second!

9. Jun 20, 2009

### Naty1

Another related interpretation has been discussed in physics forums: our speed through spacetime...in that analogy we pass thru time at "c" when stationary and our passage slows as our speed through space increases....at speed "c" thru space, our passage thru time would slow to zero....

Here is one such excerpt: (Brian Greene, THE ELEGANT UNIVERSE) :

(quoted from another thread which I just lost....)
Some pooh pooh this concept; I find it at least a very useful analogy; others are unable to conceptualize speed through time.

10. Jun 20, 2009

### MeJennifer

Point objects are lines in spacetime and spatially extended objects are like tubes. Nothing passes through spacetime with any speed as spacetime is frozen.

11. Jun 20, 2009

### Staff: Mentor

True, but you can still talk of speed in a geometric sense. Geometrically coordinate speed is the slope of the worldline, and geometrically Naty1's speed (the four-velocity) is a tangent to the worldline.

12. Jun 21, 2009

### Max™

Left is not a direction/dimension?

It is not part of Width?

13. Jun 21, 2009

### matheinste

Hello all.

Speed in the directions or dimensions x,y and z is distance paramaterized by time and so we can, if we wish have speed measured in meters per second, one meter being the unit basis vector in each of the spatial directions. I suppose that in spacetime, taking time as a dimension on an equal footing with the other three dimensions, and taking one second as the unit basis vector in the time direction, we should, for consistency, also paramatrerize it by time and so this would give the speed of time, as much as it can "mean" anything, in units of seconds per second. Thus we could give, for a clock at rest in an inertial frame a rate of 1 second per second as measured by itself, or by an observer at rest in the same reference frame.

So as has been said many times before that as much as any meaning can be attached to the question "what is the speed of time?", one second per second seems, to me, to be the most appropriate.

My apologies to any mathematicians for lack of rigor.

Matheinste

14. Jun 21, 2009

### DaveC426913

Left is a direction in a dimension. If negatron were going to be perfectly literal in correcting you, he would have said "More accurately, what is the speed of width?"

15. Jun 21, 2009

### Naty1

"Point objects are lines in spacetime and spatially extended objects are like tubes."

Isn't this like plotting the course progress of a plane on a map and proclaiming "A plane is line on a map?"

Any attempts to visualize physical phenomena, interpret and record our visualizations and represent them as mathematical formulations are designed more to represent the physical world in ways our limited senses can comprehend than they are objective descriptions. It's only we humans that seem to have trouble understanding natures rules; an atom,for example, always seems to know how its supposed to respond to forces of all types.

What does "spacetime is frozen" mean? Is this akin to "all history is fixed"?

And while some on this forum object to this concept of speed thru spacetime, it seems good enough for Brian Greene to utilize. Of course, he might be entirely wrong!

Last edited: Jun 21, 2009
16. Jun 21, 2009

### Fredrik

Staff Emeritus
I think this is the other thread. Greene's explanation is pretty misleading in my opinion, for the reasons I stated there.

17. Jun 21, 2009

### The riddler

its one second per second

18. Jun 21, 2009

### A.T.

I second that. No one objects if a plane icon is shown advancing along a path on a map. Visualizing objects as advancing in space time is no different.

Sure, you can see space time as frozen. That's the point of diagrams with time as dimensions: they describe movement with a static graph. But nothing stops you from imaging the time flow as an animated graph.

It's not question of right or wrong, but if you like this dynamic visualzation or not.

19. Jun 21, 2009

### negitron

One second per second is not a satisfactory answer because it's not a rate, it's a scale. It's no more a speed than one meter per meter is.

20. Jun 21, 2009

### A.T.

In the http://en.wikipedia.org/wiki/Geometrized_unit_system" [Broken] time has the dimensin of length, so meter per meter can be a speed. It basically means that a clock at rest advances trough time with 1 lightsecond per second.

Last edited by a moderator: May 4, 2017