I 2 objects of enormous volume each in relative motion very close to c

[ESponge2000]

TL;DR Summary

Thought experiment: Imagine a fast-moving cluster of matter and space and galaxies stars planets much like the observable universe we know but with very low density matter such that this is a super large volume (but at a fraction of the mass of our universe) ….
imagine If this cluster of galaxies were at rest with us, we would see it overlapping our entire observable universe,
But instead this ENTIRE cluster is moving in relative motion with earth at 99.9999999999999999999…% of c

So an extreme case ….. A cluster of matter and space, in direction of motion will be to us a huge huge disk with thickness of say 1 millimeter due to length contraction , traveling straight past the earth at velocity essentially c (very very very very close to c)

However, relative to this imaginary cluster , it is our entire galaxy and earth included that is a huge disk of one millimeter thick… assume then that we would observe this disk transcend our entire observable universe over hundreds of billions of years

The cluster though would travel far past our observable universe and only a fraction of a nanosecond some part of that cluster would tap Into the disk of our observable universe

In this scenario … would this be an accurate description of special relativity?

For any object in our galaxy at relative rest to earth the touch of this cluster as a disk passing at c would happen very quickly but the time for it to pass through all of our universe’s neighborhood would take billions of years

For the cluster though , eventhough their trip through our universe is that of a photon at c, where our universe is but a dot (traveling at near speed of light), the length of that entire cluster will have to cross that dot which will actually also take billions of years for its clock right ? Because while one part of the cluster is an unfathomable distance past our observable universe , another part of the cluster was way behind our observable universe and tapped into it when the disk reached it….

Is this accurate? So then there’s a certain symmetry that each part of our universe warps past a substantial part of the other universe’s entire past present and future in the moment it glides by , and vice versa each part of its own cluster takes turns getting a nanosecond to warp through our observable universe’s entire timeline in an instant nanosecond?

Again what we have think of it as a parallel observable universe to our own, but zooming past ours at so close to c that the Lorentz factor is 1 sextillion … or more than billions of billions … or such that the length of our observable universe to it is 1 millimeter thick….
Then imagine hypothetically this whole celestial cluster has a low enough density that it zooming right through earth will not destroy us but be a tap we can absorb… then how the experience of it going through our universe , and the experience to itself of us going through its universe

And would it be to say all parts of our universe would experience its entire age of existence in the nanosecond It slides by us?

Edit : wait hold on this wouldn’t be the same as the black hole theory … I believe each part of our universe will pass through the other cluster at different times on its clock but for earth we will always see the age of that cluster essentially remain frozen in the time it warped through Earth

So for the cluster’s perspective at all times the part of it that warped through our disk of a universe will forever only see that age of OUR universe frozen in time from its perspective …

 

[Dale]

If you are talking about cosmological scales you really have to talk about GR instead of SR. Does your question really require objects of cosmological scales, or would say a couple of really large volume and low mass gas clouds work?

 

[ESponge2000]

If you are talking about cosmological scales you really have to talk about GR instead of SR. Does your question really require objects of cosmological scales, or would say a couple of really large volume and low mass gas clouds work?

Let’s then use the example of a large low mass gas cloud that is the size of our solar system and zooming past our solar system at a velocity so close to C that the length contraction is 100 billion kilometers contracts to a millimeter or something like that

The SR twist here is most the time we think of a little ship or train traveling at some high velocity and has one clock time and it moves slow relative to ours,

but here I want to create the thought experiment where it’s not a little boat or train, it’s something as enormous in volume as something clone size to our world , And then do we observe a moving cloud that would be comprised of various different clocks with widely differing times but that are each moving slow but not in sync with each other ?

In an extreme velocity difference very close to c, do we cross large slice of the past present and future of this moving giant object but in the form of each particle of this moving cloud fixated each on a different time ?

 

[FactChecker]

The SR twist here is most the time we think of a little ship or train traveling at some high velocity and has one clock time and it moves slow relative to ours,

No matter what the scale of the examples, it is the different synchronization of multiple clocks in each inertial reference frame that is fundamental to the SR effects. The relativity of simultaneity is fundamental. That requires each IRF to have multiple "clocks", even if only theoretical.

 

[pervect]

If there are significant gravitational effects in your scenario, then one would need both GR and more details to answer your question. It's also h ard enough to do something like this where it's likely to languish.

If one is only interested in the special relativity aspects of the problem, studying the pole-in-barn example is sufficient. I assume you are at least somewhat familiar, if you need references let us know, though I _think_ I recall you writing a thread on the pole-in-barn example.

As a general rule, if one has a simple and well-documented thought experiment, and is seeking enlightenment, it's the wrong tack to make the simple example more complex to analyze (by adding more observers, changing the scale, or whatnot) in an effort to avoid understanding and dealing with the simple example and it's consequences. In spite of this, I see posters who have intuitive problems with the simple example doing this all time :(.

 

[Dale]

So each cloud passes through the other in a matter of a few hours (assuming the size is a few light hours in its own frame) at close to c.

As you say, the other cloud is a thin flat pancake. The clocks in the flattened pancake are not synchronized in the other frame. Clocks on one side of the pancake are a few hours ahead of clocks on the other side.

 

[ESponge2000]

So each cloud passes through the other in a matter of a few hours (assuming the size is a few light hours in its own frame) at close to c.

As you say, the other cloud is a thin flat pancake. The clocks in the flattened pancake are not synchronized in the other frame. Clocks on one side of the pancake are a few hours ahead of clocks on the other side.

Yes and the fundamental question I have is that when an observer somewhere on this cloud passes us and our solar system is the pancake , Will they also come to determine that the same events we calculate to be simultaneous between say Planet Saturn and Planet Earth, Would be not simultaneous for an observer on the cloud?

In other words , if they had a machine on this cloud with an incredibly sharp camera that can capture every photon of light assume and down to below the nanosecond would their calculated simultaneity at that very fast encounter with earth at that speed of almost exactly c, catch a different “observation of the relativity of simultaneity from their perspective between our earth and planet Saturn) “ Than do we perceive the events between these 2 planets ?

Note: The 55-minute delay or whatever it is in us observing a solar eclipse on Saturn due to the speed of light travel time to earth is not to be confused with a relativity of simultaneity difference ….. the relativity of simultaneity what events are simultaneous earth to Saturn is very much the same because the relative motion of earth and Saturn are not large enough to incur meaningful SR effects (on a scale of seconds-minutes-hours) and applying a convention of simultaneity where c is the same velocity in all directions

 

[Ibix]

In other words , if they had a machine on this cloud with an incredibly sharp camera that can capture every photon of light assume and down to below the nanosecond would their calculated simultaneity at that very fast encounter with earth at that speed of almost exactly c, catch a different “observation of the relativity of simultaneity from their perspective between our earth and planet Saturn) “ Than do we perceive the events between these 2 planets ?

What you see depends very much on light travel time. The easiest way to avoid that is to have many cameras synchronised in their rest frame taking simultaneous photos of the part of the cloud that is right in front of them.

If they do that, they would find that clocks in the cloud are not showing the same time. In general, two clocks separated by $l$ in their rest frame show a difference of $vl/c^2$, as can be read off the Lorentz transforms. For very high velocity this is indistinguishable from $l/c$. Given your stated cloud size ($10^{14}\mathrm{m}$), this works out to the clocks at front and back of the cloud being out of sync by about $3.3\times 10^5\mathrm{s}$. They advance by about $10^{-12}\mathrm{s}$ during the passage, so it should be no particular surprise that the amount of desynchronization is equal to the transit time for the cloud to pass through our stationary cloud.

 

[Dale]

Will they also come to determine that the same events we calculate to be simultaneous between say Planet Saturn and Planet Earth, Would be not simultaneous for an observer on the cloud?

Yes. It is symmetric. In our frame their clocks are desynchronized. In their frame our clocks are desynchronized.