can matter be bent in time?

[moth]

if you have a propeller spinning fast enough SR says time dilates with velocity so you get a gradient of time(s?) between the hub of the propeller and the tip.

does this mean the propeller is bent in time?

if it is bent, could it somehow be frozen in that bend so it remained curved after it stopped spinning?

would such a thing bend space?

[Pete]

if you have a propeller spinning fast enough SR says time dilates with velocity so you get a gradient of time(s?) between the hub of the propeller and the tip.

does this mean the propeller is bent in time?

if it is bent, could it somehow be frozen in that bend so it remained curved after it stopped spinning?

would such a thing bend space?

 

No. Its not meaningful to speak of something being bent in time.

Edited January 15, 2009 by Pmb

[swansont]

I think it's more accurate to say that there is a gradient in the frequencies — the rate at which time passes is different depending on your position.

 

I don't know what "bent in time" means or how to interpret it.

 

The time dilation is a kinematic effect. Once you stop spinning, every point on the propeller is in the same inertial frame, and the time dilation effect goes away.

[Dark_anzel]

i think my friend interpreted the phrase 'bend in time' in a wrong way. it doesnot mean that physical bending is seen. neither time can bend space, time is like y-axis n space's like x-axis, called fabric of spacetime.

in the process we find the gradient of time when its spining, n when it stops its all same again.the velocity of rotation changes if it convert it repective to time.

[NowThatWeKnow]

Welcome moth. What you learn here can be belittling at times.

[moth]

my math skills are non-existent so i apologize if this is nonsense.

by bent in time i mean the same thing that happens to space in a high gravity potential.

if you set up a graph with x-axis as the long axis of the propeller with the origin at the hub and y-axis as past and future with now at the origin and then plotted several points along the propeller blade as it spins around would the points with the greatest velocity move off the x-axis forming a curve in the -y direction as time slows down for them?

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thanks N.T.W.K.

the faster i'm wrong,the quicker i can move on.

[moth]

may be nobody is interested in this but i am considered a pest by many.

i found this while reading a relativity and g.p.s. link from another thread http://en.wikipedia.org/wiki/Ehrenfest_paradox

this construction seems to leave time out of the picture while implying the distance does not change(or pi is only defined for non-rotating bodies) our rulers get shorter.

a look at wikipedia topic lorentz contraction seems to also "cheat" a bit by saying you make 2 measurements (leading edge of high velocity object and trailing edge) implying two world events seperated by an unspecified amount of time.

is it just unconventional to think of this length contraction as the train cars being bent in time or is there a contradiction somehow?

[NowThatWeKnow]

...is it just unconventional to think of this length contraction as the train cars being bent in time or is there a contradiction somehow?

Contraction is only seen by an observer outside the inertial frame. I guess you would have to consider time dilation from speed and gravity. So how slow can time go?

[moth]

thanks for your reply N.T.W.K.

in the Ehrenfest setup the people on the platform see the train cars as contracted, and the people on the train see the platform as being contracted. it just seems natural to think of this as an arc in the time direction with the endpoints of the arc getting closer as the radius of the arc decreases(velocity increases).

 

So how slow can time go? the answer is here i think http://www.scienceforums.net/forum/showthread.php?t=37601

i'm still checking it out.

[NowThatWeKnow]

...in the Ehrenfest setup the people on the platform see the train cars as contracted, and the people on the train see the platform as being contracted. it just seems natural to think of this as an arc in the time direction with the endpoints of the arc getting closer as the radius of the arc decreases(velocity increases)...

 

But inside their own frame everything looks normal. I think we would have to look at the propeller as a variable frame when spinning (I don't think Martin likes "variable frame" ). From outside the propeller frame(s) it may appear to be warped but all it is doing is aging very slowly. I am trying to apply what I learned recently but still make mistakes often. Anyone want to straighten me/us out?

[moth]

it seems like the propeller blades would bend back like boomerangs as the tips slower time passage would begin to affect how much distance they could cover without exceeding lightspeed.

as for the bend in the time direction, we can't see it in our 3-d view of this 4-d bend.

picture a box sitting on a 2-d surface like the floor. the vertical dimension would be the box's height. now try and picture the vertical dimension as the length of time the box sat on that spot on the floor.kind of rotate the familiar height dimension out of view and the time dimension into it's place so you have a 2-d slice of the box (the width and the depth) for every instant the box sat on that spot on the floor in our 3-d picture.now if you could pull on the top of the box (in time) you might expect the width and/or depth to change too, and that change would show up in our everyday 3-d worldview. of course there might also be weird effects at both ends of the duration(the top and bottom of the box in the rotated time view).

Edited January 18, 2009 by moth
expanding

[npts2020]

One of your problems with visualization, IMO, is that propellers only move at a small fraction of the speed of light, making dilation effects pretty negligible. Other forces (cohesion?) overwhelm this effect.

[NowThatWeKnow]

One of your problems with visualization, IMO, is that propellers only move at a small fraction of the speed of light, making dilation effects pretty negligible. Other forces (cohesion?) overwhelm this effect.

 

I believe this is a large rocket powered propeller in space with tips reaching

.99+C to study time dilation.

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it seems like the propeller blades would bend back like boomerangs as the tips slower time passage would begin to affect how much distance they could cover without exceeding lightspeed.

 

Maybe rather then bending the propeller, the energy needed to increase speed would stop the acceleration of the propeller. Like not having infinite energy for matter to reach the speed of light.

[moth]

npts2020 "propellers only move at a small fraction of the speed of light, "

it sounds as if you're saying the solution to the Ehrenfest paradox is the train flies off the track.

what if instead of a propeller i used a carbon nanotube spinning in a magnetic field?

[npts2020]

npts2020 "propellers only move at a small fraction of the speed of light, "

it sounds as if you're saying the solution to the Ehrenfest paradox is the train flies off the track.

what if instead of a propeller i used a carbon nanotube spinning in a magnetic field?

 

I see what you are saying for theoretical purposes but I think for practical purposes that it will be extremely difficult to get something (even with the strangth of carbon nanotube) to get that much differential between any parts of a rotor. That is why I say that things like cohesion and crystal bonding will overrule quantum effects like frame of reference paradoxes (kind of like not being able to overcome friction without enough force).

[Klaynos]

Perfectly ridged structures do not exist, even carbon nano tubes. A slightly wrong but nice way of looking at it; they are held together with the EM force, this force is mediated by photons these photons must take sometime to mediate the change in position of one atom to the next, leading to non-perfect rigidity.

[moth]

thanks for the input npts2020 and klaynos

i understand you couldn't build a physical example i'm just trying to understand where the distance "goes" during lorentz contraction. lacking the math skill to solve the equation i try and model in my head and read wikipedia and of course this forum.

i'm starting to get the idea that time dialation and length contraction balance each other so lightspeed stays constant but it's a journey.

[swansont]

i'm starting to get the idea that time dialation and length contraction balance each other so lightspeed stays constant but it's a journey.

 

Yes, they do — that's how different observers can reconcile the differences in what they measure.

[Mr Skeptic]

if you have a propeller spinning fast enough SR says time dilates with velocity so you get a gradient of time(s?) between the hub of the propeller and the tip.

does this mean the propeller is bent in time?

 

I think so, in theory. In practice, there isn't going to be any material made of atoms that could withstand the stress of rotating that fast.

 

if it is bent, could it somehow be frozen in that bend so it remained curved after it stopped spinning?

would such a thing bend space?

 

No, there is no way you could preserve the bend, nor is there any way to prevent it from bending in the first place. Keep in mind that it is space itself being bent as well as anything in it.

[moth]

thanks for the encouragement swansont and MrSkeptic.

" Keep in mind that it is space itself being bent as well as anything in it."

does that mean pi has a different value on a rotating disk?or does time dilation balance the books here too?

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if i was using Lorentz equations on a rotating disk (radius=1 for simplicity) i would center the disk at the origin and look at x=0,y=1(and ignore y=1 since it's not changing much)for my x.

then calculate the velocity of the edge of the disk(pi * diameter * r.p.m.) for v(how do i tell if v is positive or negative?).

what value do i use for t?

other than that, it seems straightforward enough.

Edited January 19, 2009 by moth
clarification

[swansont]

" Keep in mind that it is space itself being bent as well as anything in it."

does that mean pi has a different value on a rotating disk?or does time dilation balance the books here too?

 

In non-Euclidean geometry, a triangle will have something other than 180 degrees in it. I don't think pi itself changes.

[moth]

the wikipedia page on the Ehrenfest paradox http://en.wikipedia.org/wiki/Ehrenfest_paradox

says Einstien showed that Circumferance = 2 * pi *r* (1−v2)^-1/2.

maybe the disk has become bowl shaped?

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if i was using Lorentz equations on a rotating disk (radius=1 for simplicity) i would center the disk at the origin and look at x=0,y=1(and ignore y=1 since it's not changing much)for my x.

then calculate the velocity of the edge of the disk(pi * diameter * r.p.m.) for v(how do i tell if v is positive or negative?).

what value do i use for t?

other than that, it seems straightforward enough.

 

ok after looking at the classical equations i see x-vt is the relative motion of the x' origin so if v=(change in x)/time, and the change in x is positive and time is positive v is positive.

also i guess any (small?) value but 0 will work for t(because at t=0 nothing has happened?) and the answer is an offset from t.

am i on the right track here?

Edited January 21, 2009 by moth
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[Daecon]

Time is only a single dimension, in order for something to be bent in time wouldn't there need to be another time dimension at right angles (or whatever) to the standard time dimension for the object to be bent into?

[ajb]

More fundamentally, I think you can to an extent think of things "bending in time" viz [math]R_{tt}[/math]= "amount of bending in time" say, i.e. the time-time component of the Ricci tensor. Why not?

 

One objection is that this does require a choice of coordinates, and so I would be careful about assigning too much to it.

 

Also, one should be careful about time as a dimension and as the (suitably chosen) parameter of time-like curves.

[swansont]

the wikipedia page on the Ehrenfest paradox http://en.wikipedia.org/wiki/Ehrenfest_paradox

says Einstien showed that Circumferance = 2 * pi *r* (1−v2)^-1/2.

maybe the disk has become bowl shaped?

 

Yes. You have to use curved space to describe the disk. That's the idea that led him to GR.