The Nature of the Universe, Time Travel and More...

[Will The Serious]

This interesting article from Space.com showed up on my Google front page.
https://www.space.com/rotating-universe-would-permit-time-travel

Most interesting to me is a recent speculation I had made about the Universe rotating based on the evidence that galaxies take on an appearance similar to rotating weather depressions. A weather depression rotates because, as the air moves to balance the pressure difference, the rotation of the Earth deflects the path to the right or left, depending upon which hemisphere the depression is in. Could this be what causes galactic spin on a cosmic scale? Does it really follow that a rotating Universe would mean time travel was possible? What other effects might this have on space, time, and perception?

-Will The Serious

 

[Asbo Zaprudder]

Hm, there are unusual correlations between the spins of members of one galactic cluster (whose designation I don't recall) that I assume might be a remnant of some condition in the early Universe. However, I don't think that Coriolis force is necessarily applicable to giving galaxies their spin. Other examples of neighbouring galaxies have opposite spins. The article points out that General Relativity is somewhat lacking in describing an intrinsically rotating cosmos. The usual assumption is that it has none as there is no universal reference frame other than the Universe itself. I don't know how one would go about deriving a suitable metric to replace Friedmann–Lemaître–Robertson–Walker (FLRW) to include rotation. Kurt Gödel tried and found it resulted in closed timelike curves as you state.

 

[Will The Serious]

Thanks for the thoughts, Asbro.

The usual assumption is that it has none as there is no universal reference frame other than the Universe itself.

Let me offer you a scenario.
Imagine a space station consisting of two rings sharing the same hub. To simulate gravity for the astronauts inside you rotate those rings, causing a centrifugal movement towards the outside of the rings. To conserve energy and reduce complexity, the engineers designed the station to spin, one ring against the other, in opposite directions. The apparent gravity would be equal to an astronaut in ring A as it would be to an astronaut in ring B. Looking out a window, each astronaut would see that the other astronaut was passing them by at twice the speed the centripetal force would indicate.

To an outside observer, they witness the effects of the forces, appropriate to each individual ring's speed.
Now, from the frame of reference of the astronauts, they are spinning at a relative speed to the other ring, but their forces are inconsistent with that relationship.

If a giant break, say a Q-like hand, were to grab onto ring A and stop its spin relative to the outside observer, to the two astronauts, nothing would change motion-wise, but everything would change, gravity-wise. The astronaut in ring A would find gravity had abandoned the ring while the astronaut in ring B would suddenly weight about twice a before. This is an example of non-relative motion. No matter how the two cylinders spin, the force effects would be consistent with their absolute speed, even if the universe were spinning or not. My point is, there would be, as you point out, no relative frame of reference, but a spin, as slow a it might be, would contribute to expansion, given an initial and unopposed velocity.

-Will

 

[Asbo Zaprudder]

Centripetal/centrifugal acceleration might superficially feel like gravitational acceleration to someone standing on the inner surface of a ring but it's not a gravitational field. A dropped object would not move as it would on a massive body such as the Moon or Earth. Various Coriolis effects would be apparent to observers in the ring although these would diminish as the ring size is increased. That we can rotate at all might well be due the presence of the rest of the matter in the Universe if one accepts Mach's conjecture. However, this conjecture has never been developed into a single, unified principle. It has various formulations that are each accepted to a greater or lesser degree as probably being valid.

Mach's principle - Wikipedia

 

[Will The Serious]

Centripetal/centrifugal acceleration might superficially feel like gravitational acceleration to someone standing on the inner surface of a ring but it's not a gravitational field. A dropped object would not move as it would on a massive body such as the Moon or Earth

True. But it would do a passable job of simulating gravity for an astronaut.

Various Coriolis effects would be apparent to observers in the ring although these would diminish as the ring size is increased.

Yes, they would be observable, if there was a Coriolis effect, but, would the diameter change it? If the RPMs remained the same, the velocity would increase, thus, the acceleration (centripetal force) would increase. That might change the effects. I don't know. I do think the effects of rotational motion are constant on the rotating body regardless of its relationship to a larger frame of reference. Rotating the Universe around a rotating body does not make the centripetal force disappear or change.

Mach's conjecture doesn't offer a mechanism, other than a philosophical point of view, to support the idea of a connection to a meta-frame of reference, with or without large distant masses. If you were to think of the greater universe of mass as a shell within which, our spinning object floated, then from a classic mechanic's point of view, the sum total of a gravitational effect upon the object would be zero.

Is Gödel's thinking about time travel reasonable? He was certainly one of the greatest thinkers of all time.

An effective rotating Universe means there is a medium, Aether, strings, geodesics, something that causes light to bend, all the objects within the rotating Universe to move with the rotation. Einstein provides that. The geodesic changes with the force and inertia behind the motion. Do we know it is reasonable to expect a geodesic to exist that would bring something like light back around into the past?

-Will

 

[Asbo Zaprudder]

If the RPM (angular velocity, ω) stays the same, the centripetal acceleration is proportional to radius r. However, usually, you want the centripetal acceleration to remain the same and it goes as rω² so ω goes as 1/√r for constant acceleration if you vary r. Suddenly stop the rotation and everything on the inner surface scrapes along the floor at a starting velocity of rω until friction or a wall stops them. Apparent Coriolis acceleration (let's ignore Euler acceleration as ω is not changing for a given r) is -2ωxν where ν is the velocity relative to the floor of the ring and x is the vector cross product. So Coriolis acceleration would also scale as 1/√r - that is, decrease with the inverse square root of the radius.

 

[Will The Serious]

An effective rotating Universe means there is a medium, Aether, strings, geodesics, something that causes light to bend, all the objects within the rotating Universe to move with the rotation. Einstein provides that.

If we assume a non-rotating beginning of an expanding universe, and that all matter is connected through some form of geodesic matrix, would the expanding universe remain static with regard to angular momentum? If the expansion was uneven, one side of the expanding universe contained more matter then the other, or one side accelerated faster, could it induce its own rotation from an internal imbalance of force?

The galaxies consistently have a disk shape and a rotational appearance. They are either created out of a spinning core, or they are drawing in material towards their centers from a tangential path.

It makes more sense that they are spewing material out as the center turns, because of the disk shape. Collecting errant material would likely result in a more globular and uneven shape. Unless there was some sort of Coriolis Effect to help organize the falling matter.

If we are to assume matter was being spewed out, and that has been the case since the galaxy core was created, and that that core came from the Big Bang, then the number of rotations since the Big Bang can be seen and the core's angular momentum would be known. They move pretty slow, if that were the case.

I recently read an article on the discovery that photon spin parity didn't hold. I am not a physicist, but I found the article interesting. This is not that article, but it also is a good one about the lost of the concept of natural symmetry. https://www.nist.gov/pml/fall-parity/reversal-parity-law-nuclear-physics. Something like this could change how we would expect larger systems to behave at their beginnings. Is there always an equal and opposite reaction? Conservation of energy should also mean a conservation of matter, since energy is an expression of the relationship of matter. Spin does not need a second particle of matter for energy to express that relationship, but every other expression of energy requires two or more particles. If spin can create an asymmetrical wave, such a phenomenon could cause the entire Universe to rotate.

-Will

 

[Will The Serious]

I am having trouble understanding General Relativity when it comes to gravity.

He (Einstein) proposed an experiment involving two elevators: one at rest on the ground on the Earth and another, far out in space away from any planet, moon, or star, accelerating upward with an acceleration equal to that of one Earth gravity (9.8 meters/second2). (Modern readers can substitute ``rocket ship'' for Einstein's elevator.) If a ball is dropped in the elevator at rest on the Earth, it will accelerate toward the floor with an acceleration of 9.8 meters/second2. A ball released in the upward accelerating elevator far out in space will also accelerate toward the floor at 9.8 meters/second2. The two elevator experiments get the same result!

Einstein used this to formulate the equivalence principle that would be the foundation of General Relativity. It states that ``there is no experiment a person could conduct in a small volume of space that would distinguish between a gravitational field and an equivalent uniform acceleration''.

https://www.astronomynotes.com/relativity/s3.htm
This one actually makes more sense than other recent explanations of the Elevator experiment I have read. At least this one doesn't claim that the bending of light in an accelerating frame of reference is unique to light or inexplicable in Newtonian Physics.

Considering that we are now able to detect gravity waves (gravitational field), would that change the Equivalence Principle? Presumably, we can now tell the difference between an accelerating frame of reference and a frame of reference within a gravitational field. The behavior of objects, such as beams or particles of light might be indistinguishable, but something behaves differently or how do we build a gravity wave detector?

The other problem I have with GR gravity is the geodesic, in general. I can understand how it might work mathematically, but what I don't understand is how does an object propelled upward by a force N from a point on the surface of the Earth, at some angle θ not follow the same geodesic every time if N changes. If a ball were thrown straight upward with a launch force of 2N, the geodesic it follows is established by the space time path distorted by the mass of the Earth and the ball. Why is that path (geodesic) unique to N?

If I stand on a sidewalk that leads me from the curb to my front door, not only does the speed with which I travel that part, not change the path I take to get to my door, but, if I stood still at the curb, and applied no force to move towards my house, it wouldn't matter how the sidewalk was twisted or curved or how much time compressed or stretched out, I would never get closer to my house.

How does curving space/time precipitate an acceleration between two bodies without constituting a force?

-Will

 

[Asbo Zaprudder]

The accelerated object is supposed to be in deep space away from a gravitational field. If it's in a gravitational field, that acceleration also applies. Some people think Einstein's original idea of a variable speed of light due to gravity was correct. That interpretation doesn't change the predicted measurements, apparently. You can find the info in videos on YouTube. Once I might have been interested in delving into this, but I'm now too old and ill to be bothered. One thing is certain - mathematics is required for effective communication and to avoid tripping oneself up with language.

 

[publiusr]

Space.com also managed to find an interview long thought forgotten
https://www.space.com/lost-georges-lemaitre-big-bang-interview-recovered

 

[Will The Serious]

What a find to come across in a closet.
I like "primeval atom". Much more descriptive than, "singularity". Maybe less accurate, considering how little we know.

-Will

 

[Will The Serious]

mathematics is required for effective communication and to avoid tripping oneself up with language.

Not a problem. Thanks for the response.

I don't have a problem with the math, only the conclusions it has brought people to. As far as the math goes, it's easy enough to work the formulas, even if I don't understand them, but I guess that's the problem. I don't understand what they are telling me.

-Will

 

[Asbo Zaprudder]

Maths is necessary for the scientific method, unfortunately. However, Karl Popper did not think Cosmology was truly accessible using that method as there is only one Universe - that we know of.

 

[Santaman]

The nature of the universe etc.. well, it's complicated..

 

[NCC-73515]

It's a sphere with a diameter of 700 m.

 

[Will The Serious]

Maths is necessary for the scientific method, unfortunately. However, Karl Popper did not think Cosmology was truly accessible using that method as there is only one Universe - that we know of.

I will have to spend more time reading up on Karl Popper. He sounds very interesting.

-Will

 

[Asbo Zaprudder]

I'd add Thomas Kuhn as well. Sometimes you've got to overturn the apple cart.

 

[Will The Serious]

It's a sphere with a diameter of 700 m.

If those measurements were taken by someone small enough to stand on the surface of an orbiting election in a local proton system and their meter was scaled to them, that would be very tiny, indeed. But if that meter were a measurement decided by a being that could run it in a few minutes, the universe is a bit bigger, but still pretty small. But, what if it was being measured by a scale where a meter was almost incomprehensible in dimension by a being that was large enough to see the entirety of the Universe with its naked eyes? Isn't size a matter of perspective?

As the Universe appears to expand, do we know our meter isn't shrinking?

-Will

 

[Asbo Zaprudder]

The metre is now defined by the distance travelled by light in vacuo in 1/ 299,792,458th of a second.

Is the universe actually shrinking? (phys.org)

 

[Will The Serious]

Paul Dirac advanced an alternative vision of the quantum world. His was based on the venerable notion that things take the path of “least action” to get from A to B — the route that, loosely speaking, takes the least time and energy.

Most intriguing is the idea that a straight line might be defined this way. I suggested such a definition in my Geometries class in college. Geometries was a class about non-Euclidean geometries. So straight lines have a slightly different meaning there.

Richard Feynman’s path integral

Yes. I can see that.

-Will