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Isotropy of the universe is the idea that the universe is the same in all directions, and is a founding principle of the laws of physics. However, that principle has been called into question by observations of galaxy cluster temperatures and luminosities.
https://scitechdaily.com/fundamental-principle-of-cosmology-cast-in-doubt-by-compelling-new-study/
"No matter where we look, the same rules apply everywhere in space: countless calculations of astrophysics are based on this basic principle. A recent study by the Universities of Bonn and Harvard, however, has thrown this principle into question. Should the measured values be confirmed, this would toss many assumptions about the properties of the universe overboard. The results are published in the journal Astronomy & Astrophysics, but are already available online."
The paper (open access):
https://www.aanda.org/articles/aa/abs/2020/04/aa36602-19/aa36602-19.html
Journal Reference (open access):
K. Migkas, G. Schellenberger, T. H. Reiprich, F. Pacaud, M. E. Ramos-Ceja and L. Lovisari. Probing cosmic isotropy with a new X-ray galaxy cluster sample through the L X – T scaling relation , 8 April 2020, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/201936602
(Score: 2) by takyon on Friday April 10 2020, @06:05PM (4 children)
AFAIK usage of a warp drive (Alcubierre drive [wikipedia.org]) would not show symptoms of time dilation. The apparent travel time would be equivalent to the time that passes for observers at the origin and destination.
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(Score: 2) by Immerman on Friday April 10 2020, @07:19PM (2 children)
Right - FTL doesn't have those problems. My point was thateven in AC's magical universe where indefinite 1G acceleration can be sustained, it's still not remotely FTL.
(Score: 2) by takyon on Friday April 10 2020, @07:44PM (1 child)
Well, you said:
"Wormholes, warp drives, etc. are all theoretically possible - they just make time travel possible as well."
I don't think an Alcubierre drive would enable meaningful time travel or backwards time travel (there is a section on the Wikipedia article discussing it). And zipping between Earth and Proxima Centauri without time dilation effects doesn't violate causality or anything.
Obviously, warp drives and wormholes may be impossible concepts. Even traveling at relativistic speeds is in doubt, since stray particles could destroy the ship. If we do create a form of FTL, it would be an exciting development, and could indicate that aliens have/are visiting Earth because it is just 2 EZ. Maybe the same could be true for reliable relativistic/0.999c travel.
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(Score: 3, Interesting) by Immerman on Friday April 10 2020, @10:26PM
>Zipping between Earth and Proxima Centauri without time dilation effects doesn't violate causality or anything.
Not obviously, no. But the speed of light is more properly termed the speed of causality, at which *every* force propagates. According to Relativity, the ability to travel even slightly faster than light, can be harnessed under carefully constructed circumstances to make a round trip that will see you arriving back at Earth before you left. It's worth reading about how it's done - it's nothing super exotic as I recall, just sending an FTL signal between three different reference frames so that the returns back to the origin before it left, and of course with an FTL ship, you are the signal.
(Score: 3, Insightful) by hendrikboom on Saturday April 11 2020, @04:23PM
The only "practical" FTL drives I've seen require large amounts of matter of negative mass.
Since FTL is equivalent to destroying causality I suspect there can be no negative-mass matter.