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Questions tagged [theories]

Questions regarding models proposed that can solve problems.

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8 votes
3 answers
4k views

Is it theoretically possible for the Sun to go dark?

If photons potentially take millions/billions of years to find their way to the surface of the Sun from the core, bouncing off billions of other atoms on their way. Is it theoretically possible to ...
Danny B86's user avatar
  • 123
3 votes
2 answers
210 views

Black hole explosion due to rotation [duplicate]

I am not an expert, I was just thinking about this scenario: A black hole that, for some reason, will start spinning faster and faster. Is it theoretically possible that the rotation becomes so fast ...
Nicola Lepetit's user avatar
2 votes
3 answers
555 views

How can Kerr black holes have a 'speed limit' to how fast they can spin?

Obviously, the speed of light is a presumed limit, at least for 'physical' objects moving 'within' ('through'?) spacetime, but... In recent news some scientists believe they have figured out the ...
Kurt Hikes's user avatar
  • 5,177
1 vote
1 answer
98 views

Why are WIMP dark matter particles, if Majorana-like, expected to annihilate upon contact? But not neutrinos?

I have heard a lot recently about so-called 'dark stars'; stars that are formed with the help of the gravitational pull of dark matter, or perhaps entirely from self-annihilating Majorana-type dark ...
Kurt Hikes's user avatar
  • 5,177
24 votes
3 answers
7k views

Is the Big Bang a theory or a model?

I ask this because someone mentioned ‘it isn't a theory, it's a model’ in the comments in an old question of mine: Is the expansion of the universe proof of the big bang? I guess defining terms is ...
Kilise's user avatar
  • 435
17 votes
1 answer
3k views

Why do cosmologists assume that inflation began shortly after the Big Bang, rather than at the exact start?

Somehow, I have never come across an explanation of why cosmologists claim that the alleged inflation of the very early universe occurred not at the Big Bang, but very shortly afterwards (~10^-36 to ...
Kurt Hikes's user avatar
  • 5,177
1 vote
0 answers
27 views

Spacetimes where symmetries vary from place to place?

Are there spacetimes or metrics where symmetries (like Poincaré, Lorentz, diffeomorphism, translational... invariances) are only local and the symmetries of one local neighbourhood are not, a priori, ...
vengaq's user avatar
  • 1,017
1 vote
1 answer
127 views

Does gravity extend out infinitely?

The sun’s gravity gets weaker the further out you go, the same goes with the Earth. But even back out all the way to Neptune and Pluto, the gravity is still there. The sun can even keep Sedna which at ...
Prince Pugs's user avatar
2 votes
1 answer
55 views

What is the relation between size (radius) of an astronomical object and the speed of oscillation of 'light' coming from it? (Strength/amplitude)?

From the year-end issue of New Scientist Magazine (Dec. 18-31,2021): Astronomy: 'Space Cow' explosion was probably a failed supernova' Page 10: 'They found that the strength of this radiation ...
Kurt Hikes's user avatar
  • 5,177
1 vote
1 answer
169 views

Do Einstein's ten field equations use 20 or 40 variables? (2 or 4 for each tensor equation?)

One site I came across says Einstein's 10 Field Equations use 20 variables, while another said 40. There are four variables in spacetime - three for space and one for time, right? But there are two ...
Kurt Hikes's user avatar
  • 5,177
1 vote
0 answers
35 views

Does the Schwarzschild metric solution require two (A and B, or g11 and g44) or four components (g11, g22, g33 and g44)?

Different places on the web imply that Schwarzschild's metric uses four components or separate equations, similar to how Einstein's full set requires 6 or 10, or they say only two are needed. Is it 2 ...
Kurt Hikes's user avatar
  • 5,177
-3 votes
1 answer
767 views

What does 's' or 'ds' or $ds^2$ mean in the Schwarzschild equation(s)? [closed]

And: These are from Wikipedia on Schwarzschild metric, Derivation of the Schwarzschild metric and the last is from Science Direct, Schwarzschild metric.
Kurt Hikes's user avatar
  • 5,177
1 vote
0 answers
32 views

How can scientists deduce the number of types of neutrinos, or 'effective number', from Planck satellite data?

Is it related to the way they deduce the Hubble constant from Planck data? Would more types of oscillating and mixing neutrinos mean faster or slower expansion of the universe? Would a fourth mass ...
Kurt Hikes's user avatar
  • 5,177
1 vote
0 answers
50 views

Why does Titan's (relatively) rapid migration away from Saturn cause the planet to wobble faster, and eventually (maybe) tip onto its side?

Over the past year and a half, multiple articles in the popular press have come out talking about how unexpectedly rapidly Titan is moving away from Saturn, and how this is causing Saturn to wobble ...
Kurt Hikes's user avatar
  • 5,177
3 votes
1 answer
399 views

Why do some call the no-hair conjecture the no-hair theorem?

This excellent answer to Why would a black hole's magnetic hair being short-lived not violate the no-hair conjecture, but long-lived hair would? How long is “long-lived”? has got me thinking because ...
uhoh's user avatar
  • 31.1k
4 votes
2 answers
619 views

How can a black hole merger create a black hole with an event horizon surface area larger than the sum of the two original areas?

Many popular and professional science sites said something about Stephen Hawking's black hole area theorem being proven observationally, finally, not just mathematically, to 95% confidence. For ...
Kurt Hikes's user avatar
  • 5,177
13 votes
4 answers
6k views

How can a black hole have a charge, or be charged?

So-called 'hairless' black holes (no-hair theory, or theorem?) , which is what real black holes are, can be described by just three characteristics: Mass, spin, and charge. It is easy enough to ...
Kurt Hikes's user avatar
  • 5,177
5 votes
0 answers
85 views

Did the density wave theory for spiral arms take account of this phenomenon?

I came across this link. In it the author speculates that in the outer region of a galaxy, the spiral arms overtake the stars, and vice versa for the inner region. That means there must be a middle ...
longtry's user avatar
  • 403
4 votes
1 answer
127 views

Can a star be massive enough to go 'supernova' yet not be massive enough to leave behind a neutron star? Or, perhaps vice versa?

From what I understand, stars that explode as a supernova at the end of their lives become either a black hole or a neutron star, and less massive stars that do not explode become white dwarves, but......
Kurt Hikes's user avatar
  • 5,177
2 votes
1 answer
85 views

In 'Modified gravity' theories like MOND, are galaxies and stars actually, slowly accelerating? In the normal sense?

In the Modified Theory of Newtonian Gravity or MOND, they say that massive objects, accelerating slowly, experience this modified gravity. But are they actually gaining in velocity, albeit very slowly?...
Kurt Hikes's user avatar
  • 5,177
9 votes
1 answer
531 views

How do comets' nuclei stick together?

Comets are commonly called icy dust balls or dirty snowballs and as such rather light: Known comets have been estimated to have an average density of $0.6 {\rm g}/{\rm cm}^3$. Because of their low ...
B--rian's user avatar
  • 5,626
2 votes
1 answer
843 views

What is the 'scale factor' equation for a dark-matter dominated universe?

The Friedmann equations can be solved exactly in presence of a perfect fluid with equation of state $${\displaystyle p=w\rho c^{2}} \qquad p=w\rho c^2$$ where ${\displaystyle p}$ is the pressure, ${\...
Kurt Hikes's user avatar
  • 5,177
1 vote
0 answers
179 views

Best response to shut down the fake Moon landing conspiracy [closed]

This Question was closed for various reasons. For people looking for the answer to similar question, please see this link. I believe this is a solid answer to my question. As the designated Space ...
Jee's user avatar
  • 245
0 votes
0 answers
42 views

Do we know what happens at the boundary of the universe, what are some theories about it? [duplicate]

Do we know what happens at the boundary of the universe, what are some theories about it? Does space time differ at the boundary? Do things become larger at the boundary? Do the trajectories curve and ...
yodicafilms's user avatar
-1 votes
2 answers
366 views

What covers the outside of the Universe? [closed]

Is the Universe a sphere with water or ice surrounding its' confinement? Are there any theories that imply the Universe being confined within a sphere of water/ice material?
Doberg's user avatar
  • 15
1 vote
1 answer
554 views

What happens if a black hole is produced inside another black hole?

Similar question here. The question I linked got me thinking. It is known that a black hole doesn't let anything escape its event horizon, not even light. Thus, naturally, anything that passes the ...
Max0815's user avatar
  • 1,862
-1 votes
1 answer
111 views

Possible scenarios for life in the death of open universe possible?

Say, let's suppose the universe ends in an open universe, with the Universe expanding, but not going to such an extent that the big rip theory will take place. Obviously, the only things left would be ...
Max0815's user avatar
  • 1,862