Physicist Claims Time Has a Geometry

sciencenews writes to tell us that a physicist at Stanford has just recently published a peer review website for several physics lectures focusing on a single underlying idea that "time is not a single dimension of spacetime but rather a local geometric distinction in spacetime." The science is presented quite clearly and originally uses GPS systems as a point of focus. From the article: "Not too long ago, people thought the Earth was flat, which meant they thought that gravity pointed in the same direction everywhere. Today, we think of that as a silly idea, but at the same time, most people today (including most scientists) still think of spacetime as if it were a big box with 3 space dimensions and 1 time dimension. So, like gravity for a flat Earth, the single time dimension for the 'big box universe' points in one direction, from the Big-Bang into the future. A lot of lip service is given to the idea of "curved spacetime", but the simplistic 3+1 'box' remains the dominant concept of what cosmic spacetime is like."

Comments

Lorentz transform anyone?

[ubiquitin]

I agree that there aren't a lot of people who intuitively reach to the Lorentz transform to explain the progression of time, but there are plenty of obvious reasons for that. Not sure it takes a Stanford physics prof. to make what is essentially a epistemological point though.

For kicks, check out one way to visualize the spacetime wheel.

Re:Lorentz transform anyone?

[ZombieWomble]

In the derivation of the Lorentz transformation (and consequently, in how most people envision 'spacetime'), we have one time 'direction', which is the same at all times, in all places - all that changes in a relativistic picture is the projection of the spacetime motion onto the time axis.

Conversely, what I think this professor is suggesting that it's not quite so simple as dealing with a single axis, but rather a collection of them, which would mean it's not possible to consider our motion through time with regard to one solitary axis, which would have an effect on many aspects of relativity (although not in the Lorentz derivation shown at the link in your post, I don't think, since in that case our spatial and time axis are simply defined as being the directions of relative motion anyhow, so there this point is moot).

Of course, I could be completely wrong, as it's nearly 2am, I haven't looked at his slides, and my report is turning my brain to mush. I'll have to have a look in the morning when it works again.

Re:Lorentz transform anyone?

[logicnazi]

You are missing his point (as the post right below you suggests). The first claim he makes is that there is a transverse red-shift from gravity in addition to the normal one predicted by GR.

In other words not only is there are redshit if we fire a lazer up into space from the earth (i.e. light leaving a gravity well) but even if we just shine a laser from one point on the earth's surface to another there should be a small redshift as well. His argument is that one would expect to see such a reshift in a accelerating frame because the light is traveling farther than it would at constant velocity.

Personally I'm skeptical of this argument at the moment because whether or not one would see a redshift is going to depend on the effect of that acceleration on the clocks. As the rocket speeds up the time dilation from SR increases as well, perhaps the right amount to compensate for the increased difference. At the very least the thought experiment doesn't produce a clear result (and it is always possible that multiple solutions are compatible with it).

As an aside the question of whether there is a global constant progression of time or it differs from location to location is just a matter of naming. The scientific community has decided to call the effects from acceleration/velocity changes in the passage of time because such a description seems to be more productive and simpler. However, one could describe the same phenomena by saying time progresses at the same rate everywhere but all physical processes slow down/speed up. Or to say it another way the Lorentzian theory of an ether with shrinking rulers and faster clocks is experimentally equivalent to SR and the same thing should be possible to do with GR (so long as there are no closed curves in time e.g. time travel)

Stepping sideways in time...

[vistic]

If time has many dimensions then I wonder why we perceive it to go forward only (though at different relative rates depending on relative speed). The reason why we perceived gravity to point down only was just a matter of not being able to see the big picture, although I would have thought more people would have noticed the Earth is round sooner, the curve is clearly visible from most mountaintops. So what's the big picture we need to see in order to see more dimensions to time? How do we step back and notice the slight curve in the horizon?

It sure seems like time goes forward only, from my own day to day observations. My mind can't even comprehend what going another direction (except for "backwards") would even mean as a concept.

Close

[jd]

Time is generally regarded as a "special case", in that it is not possible to move backwards in time, or rotate an object such that the time axis is pointing along a space axis and vice versa. Well, almost. I'll argue that it does actually allow the latter, just not in any trivial case.

Spacetime perceives time as a one dimensional vector that is orthogonal to all other vectors. Because relativistic equations for time, distance, mass, etc, use a sqare root function, you get imaginary distances and imaginary time when an object exceeds C. Usually, an imaginary quantity means that you're looking at the wrong axis.

(Trivial case in point: when solving a quadratic equation, if the parabola doesn't intersect the X axis, you will get a complex number. If you break that down into real and imaginary components, the imaginary components correspond to the displacement in the Y axis for that solution's real component value in the X axis.)

Ergo, if a tachyon exists, it would experience a spacial axis as "time" and the time axis as space, UNLESS "time" is not a single axis, in which case all bets are off.

In consequence of not having a telephone-number IQ, I can only speculate wildly, but I'm going to guess that the relativistic equations do indeed refer to some measure of bleeding between space and time and that no further dimensions are required - for GPS or for any other phenomena governed by relativity. (Superstrings being about the only exception I can think of.)

I personally think that part of the problem is that time IS regarded as "special", whereas perhaps it would be better if it were regarded as special "only as far as absolutely necessary". To the extent that specialness is an extra parameter, you want to eliminate all extra parameters as far as possible (and no further).