Does this explain what generates gravity?

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#522
Maybe just me, but I detest matrices:

https://en.wikipedia.org/wiki/Matrix_(mathematics)

OK as a computational device, but just not my sort of Mathematics.

5 Platonic Solids on Holiday.jpg


I am more a Geometer. In which 4D Spacetime includes a unique sort of thing. The 24-cell:

https://en.wikipedia.org/wiki/24-cell

This is a deal-breaker IMO. 🙂
 
#523
But matrices are your best tool to understand, and use, geometry.... I specially love Hermitian matrices...

Not to mention the best way to read the standings of La Liga... You can have a matrix that shows all the season's games. Home is X, Away is Y.
 
#525
Matrices would not work for the NFL, NBA or MBL. Only for sports and leagues where every team meets twice, home and away.

I wonder though how you'd do a matrix for an elimination tournament, specially the UEFA Champions League which has both group and home/away knock off stages and then a single final. BTW, the Spanish Coach and the Spanish Player won it... ;-)

There's a lot of gravity to MC winning a treble this year... but have no fear, Barça is quickly regaining form.

Do remember that Pep won the ECL in '09 as Barça's coach... that was the year Barça won the sextuple... I don't think ANY other team has ever done this....
 
#532
Galu said:
No one picked up on my error! That should be 70 km/s/Mpc (kilometres per second per megaparsec).

Today, space is expanding such that two objects that are 1 megaparsec apart are receding from each other at an apparent speed of 70 km/s.

This means that objects that are 2 megaparsecs apart are currently receding from each other at a rate of 140 km/s, and so on.

(A parsec is approximately 30.9 trilion kilometres or 19.2 trillion miles.)

I should get a life! 😉
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Speed of light c divided by 70km/s/megaparsec does immediately yield the so-called observable expanse/age of the universe (subject to the upper bound c on information propagation), but the universe's expansion rate is not limited by c; hence size/age aren't bound by this value, at least not determined by this formula.

In other words, 4.4 billion years in the future, the observable universe from Earth would still only be ~13+ billion light-years and it would be silly to conclude then the universe originated ~13+ billion years before. Unfortunately we weren't around when the Earth was formed; would we have observed the universe to be ~9 billion light-years in size hence logically 9 billion years old?

What an incredibly odd coincidence the Big Bang happened just at the observable limit!
 
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#537
tonyEE said:
The equations for the black hole are actually obvious... you just take the value of gravity to a given limit and you get the Event Horizon.

What happens inside is open for conjecture.

Nonetheless, the existence of phenomena that are predicted by our current model of "black holes" has been measured. Stuff like rotation of X-ray jets coming out, axially, from the accretion disk, for example.
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May be, all we call "current" is in "rotation" - like solar system:
 

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#538
wchang said:
4.4 billion years in the future, the observable universe from Earth would still only be ~13+ billion light-years
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The radius of the observable universe is 46 billion light years.

Beyond that radius, even light emitted at the Big Bang will not have had sufficient time to reach us.

The radius of the observable universe is calculated based on its rate of expansion, its current temperature and its composition - and not directly on its age.

Sounds complicated and it is!

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Perhaps we should distinguish between the 'Observable Universe' and the 'Reachable Universe'.

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#540
cumbb said:
You don't even know large parts of the discourse, like Edwin Hubble's further observations and criticism of the expanding universe;-)-;
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Hubble's Law states that the redshift in light coming from a distant astronomical object is proportional to its distance. Its acceptance lay in the fact that it corroborated Friedmann's equations which govern the expansion of space within the context of Einstein's general theory of relativity.

However, it is interesting to note that Hubble himself always held open the possibility that the cosmological redshift did not mean velocity of recession, but might be caused by something else!

I agree that we should not take it for granted that universal expansion best explains our cosmological observations and the origin of the universe.
 
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