Deep Space and Interplanetary Exploration - The Universe is Timeless

[Daryk]

Tensor Calculus and General Relativity were every-other-year courses when I was an undergrad, and I unfortunately missed them.  If I ever go back to grad school (for Physics), I'll definitely pick them up.

[Sabelkatten]

The idea that space-time is inherently warped is arguably more exotic than the alternative.

What causes this warping, why isn't it evenly distributed, how does it impact relativity if it is actually possible to determine an absolute velocity wrt space-time?

[Daryk]

I disagree.  The cosmological constant has been around a lot longer than the idea of dark matter.

[Sabelkatten]

But, at least AFAIK, the cosmological constant can't explain the measured values?

[Daryk]

It was put in as a fudge factor to get to the observed values of the time.

[Sabelkatten]

But as I understand it, it was linear. The values measured that led to DM hypothesis appears to be irregular. It would mean the constant isn't constant?

[Daryk]

Assuming it's even a thing.  My only point was that an inherently curved space time isn't that exotic.

[Sabelkatten]

Not if it's curved the same way all over, but if the inherent value isn't constant you can hypothetically identify specific point of space-time. I don't think relativity would like that.

This is of course assuming I haven't misunderstood what I've read and a constant in the formulas is actually enough to make everything add up.

[worktroll]

Interesting and valid.

Is the curvature tensor equivalent to the degree that space-time is not Euclidean? Tying back to cosmological expansion - the universe is probably either parabolic (closed universe) or hyperbolic (expanding infinitely), with all observations showing that the universe is pretty much exactly balanced between the two cases. The inflation theory gives a plausible reason for this being so - analogous to "the more you inflate a balloon, the flatter any section of the surface looks".

Parsimony of hypothesis - Occam's Razor - could be at work here?

[Daryk]

At the very least, it's so close to balanced we can't tell.

[Thunderbolt]

But as I understand it, it was linear. The values measured that led to DM hypothesis appears to be irregular. It would mean the constant isn't constant?

The Cosmological Constant (CC) accounts for Dark Energy (DE), not Dark Matter (DM) which is a separate issue:



According to the conventional cosmology, the Universe began in the Big Bang with only ~30% of required critical closure mass-energy density in the form of any kind of matter

Assumedly (?), 15% was matter and 15% was anti-matter

For some reason, all of the antimatter (15%) and 2/3^rds of the matter (10%) annihilated into "super-massive (sterile) neutrinos" or something (= WIMPs, "Weakly Interacting Massive Particles")

leaving only 5% of critical closure density surviving in the form of normal "baryonic" matter we know & love

of that 5%, 80% is intergalactic space plasma (amidst galaxies in groups, clusters, and Large Scale Structures (LSSs)), 10% is in detectably luminous bright stars (in detected galaxies), <1% is in "heavy metals" (Lithium on up) in the stars & space plasma in & amongst the galaxies, and the rest is in Cosmic Background microwave frequency photons (CMB) & normal (non-sterile) Cosmic Background neutrinos (CNB)

Professional astronomers avidly deny that much mass density resides in "dim matter" like rogue planets & Brown Dwarves (BDs) and compact objects like NSs & BHs -- if all DM were "dim matter" then there'd have to be 50x more mass out there in rogue planets & sub-stellar BDs (and NSs & BHs) than in detectably bright luminous stellar objects

(non-sterile neutrinos, including "left-handed" neutrinos = spin angular momentum points backwards anti-parallel to their velocity vector & "right-handed" anti-neutrinos = spin forward parallel to velocity, are able to interact via the Weak force... "opposite-handed" neutrinos & anti-neutrinos cannot even interact Weakly, forever isolated from any known forceful interactions... so I understand DM is not really "W-IMPs" but rather "Non-IMPs")

[Thunderbolt]

At the very least, it's so close to balanced we can't tell.

if you scrutinize the figures in most journal articles, they add up to just more than 1, so that the Universe is topologically closed and hence finite in size

[Thunderbolt]

Interesting and valid.

Is the curvature tensor equivalent to the degree that space-time is not Euclidean? Tying back to cosmological expansion - the universe is probably either parabolic (closed universe) or hyperbolic (expanding infinitely), with all observations showing that the universe is pretty much exactly balanced between the two cases. The inflation theory gives a plausible reason for this being so - analogous to "the more you inflate a balloon, the flatter any section of the surface looks".

Parsimony of hypothesis - Occam's Razor - could be at work here?

yes, essentially, think you could clarify that "space" is "(non-)Euclidean" and "space-time" is "(non-)Minkowskian", the CC would impute an "inherent" warpage or curvature into the fabric of space-time, such that even in the absence of all mass-energy, it would still be (slightly) non-Minkowskian, to a degree only observable over vast cosmic distances (or, interestingly, over deep cosmic time, space and time being largely equivalent, IIRC turns out its effects would eventually affect planetary orbits detectably, after a few eons & eras & ages or so)

[Daryk]

if you scrutinize the figures in most journal articles, they add up to just more than 1, so that the Universe is topologically closed and hence finite in size

And yet there's enough uncertainty that most cosmologists will not confidently assert the universe is in fact closed.

[Thunderbolt]

According to Curiosity Stream's "Space Junk Dangers", there are >900,000 objects in orbit around the earth the size of a marble or larger, comprising a total mass of 7500 tons equivalent to the Eiffel Tower

34,000 are larger than 4", of which 23,000 are monitored by the US

the Indian Shakti test created an additional 4000 pieces of debris, 400 larger than 4", the blast kicked the debris of the satellite out from a 300km circular orbit to highly elliptical orbits ranging from 300-2000km altitude... the orbits will re-circularize over a few years and then quickly decay and the pieces will burn up in the atmosphere

How much space debris might there be in orbit around IS worlds after a thousand years in space ???

[Thunderbolt]

And yet there's enough uncertainty that most cosmologists will not confidently assert the universe is in fact closed.

and the slight density difference makes negligible difference to any observable back to ultra early epochs, yet the tacit private preference appears to be for a finite & closed cosmology

[Daryk]

Tacit is the key.  I put it in the "probably" category, not "certain".

[Thunderbolt]

Tacit is the key.  I put it in the "probably" category, not "certain".

you and everyone else

hard to imagine any actually infinitely infinite anything, generally infinities are acknowledged as regimes wherein the theory in question breaks down

[Daryk]

I was lucky to be introduced to infinities in 8th grade when my math teacher lent me a book on the topic.  Truly mind expanding, as they say.

[Maingunnery]

According to Curiosity Stream's "Space Junk Dangers", there are >900,000 objects in orbit around the earth the size of a marble or larger, comprising a total mass of 7500 tons equivalent to the Eiffel Tower

34,000 are larger than 4", of which 23,000 are monitored by the US

the Indian Shakti test created an additional 4000 pieces of debris, 400 larger than 4", the blast kicked the debris of the satellite out from a 300km circular orbit to highly elliptical orbits ranging from 300-2000km altitude... the orbits will re-circularize over a few years and then quickly decay and the pieces will burn up in the atmosphere

How much space debris might there be in orbit around IS worlds after a thousand years in space ???

I imagine that most planets can hire some Small Craft to clean up their local orbits.

[Daryk]

Heck, even a "fighter" could do the job (eventually).

[Wrangler]

Isn't there alot legal issues if companies start removing space junk from decommed or malfunctioning space debris/junk?

[Cache]

Isn't there alot legal issues if companies start removing space junk from decommed or malfunctioning space debris/junk?

International waters. Salvage rights and all that.

[ANS Kamas P81]

Assumedly (?), 15% was matter and 15% was anti-matter

More like 15.0000000005% was matter and 14.9999999995% was antimatter, just to be pedantic.  However that too is what drives astrophysicists nuts.

[Thunderbolt]

More like 15.0000000005% was matter and 14.9999999995% was antimatter, just to be pedantic.  However that too is what drives astrophysicists nuts.

well, if want went in were even amounts of M&AM...

And what came out was 25% DM and 5% M

And if mass is conserved, then what went in was 15% / 15% ?

I know that is what they always say, but isn't the leftovers our 5%?  So the most lop sided it could have been was 52.5-47.5 ?  And that only if there was no DE which is 70% of the total

You have to get 5% M to survive

Not 0.00005%, though that is the impression always given

Maybe electrons are matter, and the quarks in protons are antimatter "with a twist" such that even amounts are in fact present?  Positrons are AM, and anti protons are really M?

[Wrangler]

International waters. Salvage rights and all that.

You could end up scooping up billion dollar spy sats that aren't dead. 

[Cache]

You could end up scooping up billion dollar spy sats that aren't dead.

If you're "removing space junk from decommed or malfunctioning space debris/junk" I should hope you know better than to pick up operating sats. It would be the salvage crew's responsibility to know the difference. Also, anybody putting up expensive spy sats like that should very well have a tracking system where they can see a salvage operation getting close, and issue warnings.

[Maingunnery]

If you're "removing space junk from decommed or malfunctioning space debris/junk" I should hope you know better than to pick up operating sats. It would be the salvage crew's responsibility to know the difference. Also, anybody putting up expensive spy sats like that should very well have a tracking system where they can see a salvage operation getting close, and issue warnings.

Any sats that pretend to be dead, are pretending at their own risk.

[kato]

International waters. Salvage rights and all that.

[Daryk]

Right, piracy it is, then!  >:D