Instantaneous travel of macroscopic objects?

[Tormod]

Tormod:

 

Hmm but is it correct to say that you traveled back in time?

 

Notice I wrote that I would appear to have traveled back in time, because we could still look through the telescope and see my spaceship being close to the sun for another 8 minutes (until it vanishes). For all practial reasons I have travelled back in time with the only exception that I appear on Earth _after_ I relocate from the Sun, not before. Travelling at the speed of c would take me 8 minutes (plus of course the time it takes to accelerate and decelerate).

 

All that really happened is that those on Earth were not able to find out about your whereabouts due to the fact that you were now the “fastest moving reference frame”, and not c.

 

No, they know where I am all the time. If they were looking at my ship through the telescope they would know I am close to the Sun. Also, my radio signals would inform them that I would come back in 8 minutes (if I chose to say so). Then in the next instant I'd be right next to them. So they would see me as being in a spaceship hovering above the sun even as they were talking to me in the same room.

 

And here is the time travel part: After 8 minutes of talking to me, they see my ship vanish from the Sun. Thus I appear to leave the Sun 8 minutes after I arrived at the Earth.

 

I am not (in) the fastest moving reference frame at all, since I did not move through space-time (like sanctus pointed out).

 

Just because those back on Earth did not know about the sunspot did not stop it from being there, just as if the sun suddenly exploded, you would not say that just because we saw it only eight minutes later, it traveled back in time.

 

No, but I would be able to tell them when it was due to appear because I had observed it myself just seconds before, millions of kilometers away. So the information has moved faster through the wormhole than the light itself has moved from the Sun to the Earth.

 

I think you fail to see my point that we are talking about two things:

 

1) I move from A to B faster than light, thus violating the speed limits in the universe

 

2) ...However, I am using a trick (skipping the space dimension) so my timeline is ticking away at a normal rate relative to the Earth. No time dilation, no movement in space.

 

Your scenario only seems like time travel because you are actually introducing a speed above c, which is our basic (observed) speed limit. Do you see what I’m getting at here? It’s only “time travel” because you’re hypothetically traveling faster than the fastest speed, thus introducing a new “fastest speed” – instantaneous travel. If you accept this as your new speed limit, you can see that the situation can no longer be thought of “time travel”.

 

As far as I can see this is simply a rephrasing of what I wrote in my post. B)

 

Anything ABOVE this speed, however, WOULD be considered time travel as it would be faster than instantaneous, which means literally arriving before you started out, and without any relativistic tricks.

 

Yes. But it would also mean that you would need to travel in space, which I do not do in my example (I simply relocate).

 

Remember the discussion you started was about whether macroscopic can move instantaneously in time. My example shows a hypothetical situation in which this happens, and I then ask whether it is the same as time travel, which it is not - it requires a wormhole, which I was then asked to clarify (which I hope I have done).

 

I still question your opening statement that Einstein wrote that objects can move instantaneously in time. I have never seen this be written anywhere. I wonder if you are confusing "movement" in this case with "wave diffusion" - Newton believed gravity was instantanous over infinite distances, wheres Einstein proved that this was not true.

 

However, I am of course only happy to be corrected here. B)

[paultrr]

I'll attempt two answers at once here.

 

1.) Its an observational apperant version of time travel without actually going into the past as far as the craft is concerned. The craft at some point in its history saw an event. It then jumped to earth in zero time. So we have T+0 at this point for the craft. Those on earth watch the sun and the craft. At some point the craft vanishes from around the sun and appears instantly at the earth. Again we have T+0 on our clocks. The craft discribes an event at the sun. Eight minutes later that event is witnessed on earth. So we now have T+0+8 for the earth and the craft also. But the craft left the sun before the earth saw this event and yet, it left right after the event there. So for the earth's frame of reference the craft seems to have traveled back before the event. But the difference is found in the time it took for that event to be viewed on earth.

 

2.) The Planck scale is not a zero itself. It would not be a singularity at all of zero dimensions by any present accepted version of quantum theory including Loop Quantum Field Theory. Yet, the odd microscopic effets mentioned earlier by theory begin at that scale, not at an actual zero point.

[gpdone]

Thank you Tormod. You put it very well. Paultrr restated it correctly as far as I can tell with one goof;

 

'At some point the craft vanishes from around the sun and appears instantly at the earth.'

 

Literally this is incorrect. The craft would appear first at the earth and THEN vanish from around the sun eight minutes later.

 

In all cases, as far as I am concerned, only apparent time travel has occured.

 

Lee

[DivineNathicana]

I still question your opening statement that Einstein wrote that objects can move instantaneously in time. I have never seen this be written anywhere. I wonder if you are confusing "movement" in this case with "wave diffusion" - Newton believed gravity was instantanous over infinite distances, wheres Einstein proved that this was not true.

 

You misread:

 

Einstein said that instantaneous travel was impossible.

 

And yes, I did not realize you would not actually be travelling through spacetime. But here's a follow-up question: No matter how short a wormhole may be, why would it be instantaneous to travel through one? It still has length. We've just figured out that no matter how small a distance between A and B is, it will still take up time. So why not a wormhole?

 

- Alisa

[DivineNathicana]

Sanctus,

 

What if you're going in accordance with ST, which doesn't permit any length above h-bar? If travel between points A and B Planck's length away from each other is not instantaneous, then why not stop along the way and have ourselves a length below the Plaqnck's length?

 

Logically, it makes sense that two points h-bar distance away from each other are farther away than two points that are "right next to" each other, the latter theoretically being instantaneous... But If this were so, then why can't we have even shorter lengths?

 

- Alisa

[paultrr]

Both string theory and LQFT propose further sub-division. The biggest difference is one rather sees things as a continum on down ward while the other proposes there is a minimual length and time unit to how small things get. You can in theory get to a point unless for instance the Planck scale is the boundary of an embedded spacetime or hyperspace itself. In this case, for our spacetime the Planck scale is the mimumal unit while everything smaller could actually be a larger spacetime that may encompases not only our universe as well as other universes. Here again it would be our frame's structure and boundary conditions that makes the other look smaller than it is. If that is the case then we really do have a continum in both directions to deal with.

 

Basically, its true that untill we can measure such scales directly or someone figures out how to enlarge the planck scale and its effects any movement there makes little difference for you and I. But in theory its possible there is movement there that at least for microscopic objects might be instantaneous.

[DivineNathicana]

Basically, its true that untill we can measure such scales directly or someone figures out how to enlarge the planck scale and its effects any movement there makes little difference for you and I. But in theory its possible there is movement there that at least for microscopic objects might be instantaneous.

 

Wouldn't it be logigal for us NOT to be able to "measure" such scales if they are smallest possible distance as then we will label them with a length (or a line segment, consisting of two points and a LINE of a certain LENGTH between them), and they should thus be able to be broken up further (a third point somewhere on the segment)?

 

And going totally off thread but on par with my latter comments: If strings have length, why are they fundamental and as short as anything gets? And how can a string be 1D anyway? How can something 1D vibrate?

[Tormod]

You misread (the Einstein thing)

 

Oooops. Sorry Alisa! That's what I get for staying up too late... B)

 

But here's a follow-up question: No matter how short a wormhole may be, why would it be instantaneous to travel through one? It still has length. We've just figured out that no matter how small a distance between A and B is, it will still take up time. So why not a wormhole?

 

- Alisa

 

Well, this is purely hypothetical but a "wormhole" actually has no length.

 

This is the best analogy I can give you:

Take a sheet of paper and use a pencil to mark an "A" at the top of the paper and another "B" at the bottom of the paper.

 

The shortest distance from A to B is now the length of the paper.

 

Now fold the paper so that A and B are on top of each other. Take your pencil and punch a hole through the paper. This is your wormhole.

 

A wormhole is not a tunnel but a "hole" through space-time, so that when you enter it you instantly exit somewhere else. Thus you can now travel from A to B in an instant, without even having to bother about the rest of the sheet of paper.

 

There are of course other theories about wormholes so this is just one example, but it is a good analogy for the example I used.

[paultrr]

Strings are 1D, then you have branes which while under M-Theory started out as 2D now have evolved into objects of many different dimensions. You can also add in instantons and the list goes on, so to speak. As to what's minimual? Well, the average as far as theory goes for the fundamental length of strings is around that of the planck scale. However, that is an average and there are some theories out there with even smaller scales. Generally, at least as far as those compacted extra dimensions the scale runs from near that of planck on downward. If you throw in the idea of large extra dimensions that are hidden from us you get all sorts of possible answers.

[paultrr]

The usual method of modeling dark energy is as an ideal fluid where the equation of state(EOS) is:

 

Pd=wpd.

 

Here Pd and pd represent the energy density and the pressure. The current thought on w place it less than -1/3 at the current time. Almost irrespective of the cosmological model or weither the equation of state is a real variable over time cosmological date(see WMAP) constrains set w at around -1. So some version of both dark matter and exotic energy is at play in our universe. Once one opens the door to exotic energy even of the negative vacuum pressure type which the above modeling allows then theoretical states like wormholes, enlarged planck regions, etc become theoretically possible even if we have no present means of detecting them directly.

 

The problem we face is finding an exact model that not only fits all the cosmological data but which explains things beyond the standard model for particle physics. We also have the side problem of finding a model that allows for some local violation of known energy conditions without creating global violations of such. But the implcation is very strong at the present that the overall EOS for the vacuum itself does vary. It's the how much it varies locally and that variance effect on global scales that dictates the idea of there existing frames of reference where C is no longer a constant. As for wormholes or other exotic states being possible the fact that exotic energy of some type exists rather makes the other possible at least as far as microscopic scales go.

[Bo]

How could the wmap data constrain w? as far as i know, WMAP showed that the universe is flat (Omega=1.05 or something like that) and expanding. Expanding universes require some sort of vacuum energy with w<-1/3 or, for prolonged inflation: w<-2/3. I dont think WMAP says that we need -1, which would mean a pure cosmological constant, but just requires w<-2/3

 

negative vacuum pressure type which the above modeling allows then theoretical states like wormholes, enlarged planck regions, etc become theoretically possible even if we have no present means of detecting them directly.

 

i dont see any direct link between negative vacuum pressure and wormholes. negative vacuum pressure acts, just like normal matter, on the expansion of the universe. Large anisotropies could cause things like wormholes or whatever, but that holds both for positive and negative pressure.

 

Bo

[sanctus]

Sanctus,

 

What if you're going in accordance with ST, which doesn't permit any length above h-bar? If travel between points A and B Planck's length away from each other is not instantaneous, then why not stop along the way and have ourselves a length below the Plaqnck's length?

 

I haven't done any general relativity yet (have to wait for next year :wink: ) and I guess your statement from minimal lenght comes from there; I have to say though it surprises me very much that a minimal length exists, I thought it was continous....

[paultrr]

The general idea of a minimual length comes from Loop Quantum Field Theory which was popularized a bit in Lee Smolin's account in the book, "Three Roads to Quantum Gravity." Personally, I do not actual subscribe to that camp fully even though at times I find the geometry side interesting and having some merit. You do not find it under General Relativity where in general spacetime is a continium.

[DivineNathicana]

Oooops. Sorry Alisa! That's what I get for staying up too late...

 

It's okay, Tormod, I don't sleep either. = ) No one in New York does.

 

I haven't done any general relativity yet (have to wait for next year :wink: ) and I guess your statement from minimal lenght comes from there; I have to say though it surprises me very much that a minimal length exists, I thought it was continous....

 

Sanctus,

 

This is due to the R and 1/R winding modes duality of strings. Basically, to put it in the simplest terms, there are two types of string configurations that can be used as probes to measure distance: wound and unwound configurations. They will yield reciprocal results, but we only use the "light" configuration - the unwound ones, as they are relatively easy to carry out with the wound ones are "heavy" and are still beyond our technological abilities.

 

As we measure smaller and smaller distances, the results near each other both in numerical value and in level of computational difficulty, until they reach a point at which they are in a 1/1 relationship (h-bar), since 1 is its own reciprocal. However, AFTER that, the unwound modes become the "lighter" and more easily computed ones, and the unwound ones become "heavier".

 

Since we only use the "light" configurations as probes, we never obtain a length below that of the Planck's length. It's like a "bounce effect" - as soon as we get to the Planck's length, our measurements automatically become increasingly larger, thus preventing us from (hypothetically) probing to smaller length scales.

 

However, I don't particularly like that model as just because we are as of yet unable to compute heavy string configurations, that does not prevent them from existing - and both the R and 1/R measurements are perfectly credible.

 

P.S. Check out Brian Greene's "The Elegant Universe". It gives a very clear explanation of the above.

 

Hope I helped,

 

- Alisa

[Keebs]

The reason an object doesn't travel instantaneously is because velocity is defined as dx/dt, and written in limit notation you find that as the change in time approaches 0, so does the change in displacement. So, if you don't travel forward in time at all (instantaneously), you won't travel forwards in space at all either.

[paultrr]

If deltax is too small compared to the length scale I’m interested in, I could say something exists at X. This is a typical statement made by classical physics. Although such an overly precise statement is incorrect because it implies that the entity is of zero size (i.e., Deltax=0); it is a good enough description of reality without undesirable consequences. But if deltax is significant compared to the length scale that I'm interested in, ignoring it is no longer an option. At near planck scales the problem is if there is something I’m trying to measure at X, but its existence is spilled over to its neighborhood, and the total range is deltax. This bias towards the center forces one to say, there are different levels of existence of the quantum thing within the confinement of deltax.

 

Classical physics then leads one to a problem. Since the quantum thing is in motion with velocity v, if I call the time corresponding to the leading edge and trailing edge of the quantum thing tl and tt respectively, I should get:

tl = tt + deltax/v .

The logic of classical physics would force me to accept that the leading edge of the quantum thing is formed first, and the trailing edge is formed at time deltax/v later. To get the right picture the quantum thing must be seen as existing as an instantaneous whole. This much is standard quantum theory and where quantum theory and relativity always diverge. It was also a point of contention between Einstein over quantum theory to begin with. To recover the classical picture what we are forced to do is impose those limits on the smallest unit of time and space. But that is only required to get the classical picture. Its not actually required by the theory itself. Within quantum theory the wave function spread across the whole of deltax and beyond and the quantum thing remaining an instantaneous whole untill observed remains true.

[paultrr]

One solution around this, the one used under DSR is to impose two frames of reference. One for classical spacetime and one for quantum spacetime. The only general problem with this approach is that we still encounter an infinite spread at the planck scale itself. That's why most versions of DSR tend to have that scale as the limit of the second frame of reference. Usually its the energy that becomes the measuring rod for that second frame. By theory and math at the planck scale since the wavefunction spread is to infinity its actual energy is spread to infinity. But even in what appears like zero time if one where to slice that spread out one finds there is residual potential energy at every point. And if you take the sum of that spread you recover the initial energy anyway. So at the very least anything spread across deltax has across that spread its same initial energy even though we cannot measure the time interval. If the energy is there then what we are trying to measure is there also. That means that quantum theory is correct and the quantum thing is the instantious whole irrespective of weither this fits the classical picture or not.