Terrell Revisited: The Invisibility of the Lorentz Contraction

[Ken G]

Yes, it is remarkable how "slow" the universe usually is at the macro level. The universe has a fundamental speed limit that individual particles (especially light, but also electrons) routinely encounter, but it rarely produces encounters between macroscopic objects at anything close to that speed limit. You'd have to look near very strong gravitational sources like black holes and neutron stars to find encounters between macroscopic objects that probe anything close to the speed limit. The possible phase space is very sparsely populated at the macro level!

 

[PAllen]

Yes, it is remarkable how "slow" the universe usually is at the macro level. The universe has a fundamental speed limit that individual particles (especially light, but also electrons) routinely encounter, but it rarely produces encounters between macroscopic objects at anything close to that speed limit. You'd have to look near very strong gravitational sources like black holes and neutron stars to find encounters between macroscopic objects that probe anything close to the speed limit. The possible phase space is very sparsely populated at the macro level!

As I recall, even for an object free falling to a neutron star surface, the speed reached is at most .5 c. Speed of 1/3 c is considered more typical of neutron star escape velocity.

 

[Ken G]

Yes, and though presumably there is a range of masses for neutron stars that push the escape speed right up to c, these are still unusual environments for macroscopic objects to ever encounter. Most of the macro objects in our universe will never encounter any other macro objects at relative speeds larger than perhaps 0.001 c or less. That includes intelligent observers, who might never pass each other at any faster speeds than that, for all we know. So we have the odd situation of a theory built to talk about encounters like 0.999 c, yet it hasn't been tested (for macro object encounters) at speeds larger than maybe 0.0001 c. We have no reason to think what works for individual particles won't work for macro systems, but JDoolin's simulations here haven't been seen with our own eyes, if you will. That may be the real reason length contraction is "invisible"-- there just aren't situations where you can see it!

 

[JDoolin]

There's "superluminal jets":
The superluminal jets probably consist of particles--not individual macroscopic objects. And high redshift objects, such as distant supernova with z>7, and CMBR with z>1000.
The high redshift objects are traveling more than .866c but straight away from us.

 

[John F. Gogo]

Yup, those would be the variants with significant historical basis.

For the purposes talking about observability of length contraction, I therefore made explicit I was talking about a frame where light speed happened to be c and was isotropic, but that object's geometry was unaffected by motion. Thus (3), in the aether frame. (1) would be trivial, (2) would be more complex as would (3) in any frame other than the aether frame. In any case, what I proposed is the clearest way to contrast what you would see without length contraction.

I would go with the trivial.

 

[Ken G]

And high redshift objects, such as distant supernova with z>7, and CMBR with z>1000.
The high redshift objects are traveling more than .866c but straight away from us.

I wouldn't count that, only macro objects passing each other at the same place and time with a relative speed. Cosmological redshifts are generally not regarded as high-speed motion, but rather a dynamical change in the metric that determines distances.

 

[PAllen]

There's "superluminal jets":
The superluminal jets probably consist of particles--not individual macroscopic objects. And high redshift objects, such as distant supernova with z>7, and CMBR with z>1000.
The high redshift objects are traveling more than .866c but straight away from us.

I explicitly said "near earth", which is what would be needed to try to photograph the effects you've been simulating.

 

[PAllen]

I wouldn't count that, only macro objects passing each other at the same place and time with a relative speed. Cosmological redshifts are generally not regarded as high-speed motion, but rather a dynamical change in the metric that determines distances.

And that is a matter of contention, which I would rather not hijack this thread to discuss. A consensus position is that relative velocity of distant objects simply has no well defined meaning.

 

[JDoolin]

I explicitly said "near earth", which is what would be needed to try to photograph the effects you've been simulating.

About 53 million light years away, M87 has a superluminal jet that is large enough to distinguish some macroscopic detail.

http://spiff.rit.edu/classes/phys200/lectures/superlum/superlum.htm

Now that doesn't occupy a large solid-angle, but it should still show the stretching and compression along the axis of it's velocity.

The jet is simultaneously being shot out from both sides of the active galaxy, which would provide a dramatic difference between the jets moving away, and the jets moving toward us.

We might not see the superluminal jet "go by" like this abstract object does here:
http://www.spoonfedrelativity.com/web_images/ViewFollowing19.gif

But we would still observe whatever details are present in the approaching cloud, stretched out by the superluminal effect, and on the other side, flattened by the combination of the recession effect and the Lorentz Contraction effect.

So, for instance, why here, does the jet seem to only come out of one side of the galaxy? Is it an asymmetrical event, or is it actually coming out of both sides, equally, but our perception of the receding jet are so slowed that we can't see it yet?

 

[PAllen]

Well, the other jet would be red shifted and dimmed versus blue shifted and brightened. Don't know that fully accounts for no visibility, but it would certainly contribute. There is a large component velocity towards us for superluminal apparent motion.