Interesting relativity idea here

[silverpig]

Okay, before I give you my idea, I have a question. Relativistic speeds lead to length contraction of the travelling object along the axis of travel. Why? What is the physical reason for this to happen? Is it just an effect that occurs, or is there a physical explanation for it?

(Don't dumb down your answers for me either, I'm a physics/astro honours major)

I have an interesting idea that may explain it, but need a bit of help working through some details.

 

[Elledan]

If you really want an in-depth answer, check out Physics Forum

 

[Mday]

length contractions are noticed by an observer at a non relativistic reference point.

There is no real PHYSICAL explanation, but if you work out the math through the equations, you do get length contractions. just like for quantum mechanics, there is no PHYSICAL reasons why electrons "disappear"

of course it depends on what you mean by physical...

 

[silverpig]

Damn, no time before work. I'll post when I get home.

 

[rimshaker]

Funny, i wondered about the same thing when i first learned it. I can pretty much accept the time dilation part, but the length contraction is something 'physical' so i had a harder time just letting it be. No breakthrough technical reasoning here... i just imagined a kind of 'relativistic wind' where an object is going so fast, that matter gets squeezed, or pushed, together momentarily.

Hmmm... what's your interesting idea?

 

[silverpig]

Okay, here's a somewhat thought out theory...

Don't mock it until you see how it can explain some things.

It's called the expansion of everything theory. Basically, scientists have known that the universe as a whole is expanding. It's not as though the centre is static and the "outer edges" are getting farther away from it, but rather that the entire fabric of space time is being stretched out like a balloon so that every point in space is moving away from every other point. It was thought that condensed objects like people, planets, solar systems, and even galaxies were held together by gravity and were not flying apart due to this expansion.

Well, maybe EVERYTHING is expanding, people included. I'm saying that perhaps our molecules are expanding, but so is the space between them, all at a rate that is proportional, and so we keep our shape (I can explain further if required for clarity).

Where this comes in to the physical contraction of objects at relativistic speeds is this:

Take a spherical object and let's say it is expanding at a radial velocity of v. In relation to the centre of the object, the point on the surface of the sphere along the positive x-axis is moving at a velocity of +v, and the opposite point on the negative x-axis is moving at a velocity of -v. Now, move this object as a whole along the positive x-axis at velocity u.

Now using the relativistic velocity addition equation, you can see that the difference between the relativistic addition of u + v [rel(u+v)] is less than 2v more than the relativistic difference between u - v [rel(u-v)].

Normally, you have:

u + v - (u - v) = 2v

but using relativistic addition you have

rel(u + v) - rel(u - v) < 2v

Where this leaves us is that because the object is not moving in the y- or z-directions, the difference between the expansion rates of opposing sides in those directions is 2v, while in the x-direction, the expansion is less than 2v, thus, leading to an apparent contraction in that direction.

This is really rough, but it has some potential.

 

[Sohcan]

It's an interesting idea, but....

Isn't the Hubble expansion something on the order of 100 km/sec/megaparsec? That's 100 km/sec per 3.26 million light-years....that means, assuming I'm two meters tall, that my feet are expanding away from my head at about 6*10^-18 m/sec (6 billionths of a nanometer/sec!). That's essentially zero, especially in terms of c.

Using relativistic velocity transformation along the z-axis, there's still going to be essentially zero difference between the expansion of the length of your body, despite that your apparent length should contract by the factor 1/gamma...also, it would imply that larger objects would undergo a greater length contraction at the same speed of a smaller object, something that special relativity at least doesn't predict....

edit: toying with some numbers here....let's say the middle of my body is at the origin, and I'm "lying" on the x-axis. The velocity of the expansion of my head is 3*10^-18 m/sec = 10^-26 c, and of my feet is -10^-26 c. Let's say we transform to a frame moving to the +x direction at .8c.

The transformed velocity of my head is (10^-26 c - .8 c)/(1 - 10^-26 c * .8 c / c^2) which is essentially -.8 c
The transformed velocity of my feet are (-10^-26 c - .8 c)/(1 + 10^-26 c * .8 c / c^2) which is still essentially -.8 c

 

[Shalmanese]

<< It's an interesting idea, but....

Isn't the Hubble expansion something on the order of 100 km/sec/megaparsec? That's 100 km/sec per 3.26 million light-years....that means, assuming I'm two meters tall, that my feet are expanding away from my head at about 6*10^-18 m/sec (6 billionths of a nanometer/sec!). That's essentially zero, especially in terms of c.

Using relativistic velocity transformation along the z-axis, there's still going to be essentially zero difference between the expansion of the length of your body, despite that your apparent length should contract by the factor 1/gamma...also, it would imply that larger objects would undergo a greater length contraction at the same speed of a smaller object, something that special relativity at least doesn't predict....

edit: toying with some numbers here....let's say the middle of my body is at the origin, and I'm "lying" on the x-axis. The velocity of the expansion of my head is 3*10^-18 m/sec = 10^-26 c, and of my feet is -10^-26 c. Let's say we transform to a frame moving to the +x direction at .8c.

The transformed velocity of my head is (10^-26 c - .8 c)/(1 - 10^-26 c * .8 c / c^2) which is essentially -.8 c
The transformed velocity of my feet are (-10^-26 c - .8 c)/(1 + 10^-26 c * .8 c / c^2) which is still essentially -.8 c >>



Well, first of all, the Hubble Constant is closer to 65 and second of all, the hubble expansion doesnt work for anything less than Galaxy size due to gravatational binding.

 

[Sohcan]

<< first of all, the Hubble Constant is closer to 65 >>

Hence "on the order of" ....my point remains the same.


<< the hubble expansion doesnt work for anything less than Galaxy size due to gravatational binding. >>

I know, I was assuming that silverpig's supposition to the contrary was true with regard to relativistic velocity transformation...read his last post.

 

[silverpig]

What if the Hubble Constant is due to actual motion due to the newly suggested repulsive force of a vacuum and not spatial expansion? True, my supposition would mean that everything was expanding outwards at a very high velocity, but the big bang was incredibly powerful...

I'm not saying that this is what I believe, but I thought it'd make for interesting discussion.