When children are overwhelmed, they should also get out under the fusion reactor sun, another figure in the ballon popping tale;-)
But, fusion is happening in either theory... either it's in the core of the sun or up in the photosphere and chromosphere.
So enjoy your fusion.. down here in Coastal SoCal we've had a deep marine layer that means our Gray May is progressing into a June Gloom. I think we've had about 24 hours of cumulative sunshine since April. At least my tomatoes had some success in achieving fusion and we have some fruit growing.
Well, it's hard to tell what he/she/they (not to make assumptions!!) means... 😀 But I thought "But you explain once LIGO, please;-)" wasn't too ambiguous...
Ta! We're currently having a heat wave in Scotland.
I'm fair skinned so have to stay out of the direct fusion glare, from wherever it actually happens to emanate!
Scorchio! is the cry, and a far cry it is from the usual Scottish weather!
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(ANNOTATION INSERTED ABOVE）
Billions of years in the future, the observable universe will STILL BE constant c/Hubble's Constant in radius ~14BLY. There's no way to deduce from only HC the age of the universe UNLESS the BB is younger than the observable limit timewise so its photon or gravity wave could in theory reach us.
There seems to be a theoretical model of the BB's echo cosmic background radiation that yields an age of ~14 billion years.
Everything hinges on the exact value of the Hubble constant (H).
Using H to extrapolate back to the Big Bang depends upon the current density of the Universe and on the composition of the Universe, so we can't yet be certain about the age of the universe.
The current best estimates of H give an age of between 10 and 20 billion years.
If the age of the Universe is as small as 10 billion years then it would be shorter than the age of its oldest stars. This contradiction would imply that the Big Bang theory is incorrect.
Obviously there is still argument regarding the rate of expansion of the universe. The crux of the matter is that the measurements being made depend on the size of the data base, and that data base is improving as physicists work on the problem. Perhaps one day we will have sufficient data to make a final decision on the rate of expansion of the Universe - I fear that's unlikely to happen in my lifetime!
No, a TRILLION years in the future the observable universe will still be ~14B assuming Hubble is close to being constant. The calculation c/H is "oblivious" to WHEN it is done (no time reference), so AGE cannot possibly be derived from it unless BB < c/H. No amount of future technology observation could possibly yield "farther/older" direct photons than c/H and our present technology observation already approaches c/H. A photon that is beyond c/H will never reach us because its distance to us forever increases! Assuming Hubble of course--but H needs not be a constant only bounded, and the argument still holds.
From what I read (I'm not an astrophysicist!) the Hubble radius is 14.4 billion light years and, since it is calculated from r = c/H it always will be, provided the Hubble constant remains the same value in the future.
I think we are in agreement here, other than in your use of the term observable universe, since the Hubble radius delineates a spherical volume within the observable Universe.
The term c/H represents a distance beyond which objects recede from the observer at a rate greater than c due to the expansion of the Universe, so light from them can never reach us.
I think we are in agreement here also.
Short summary;-)
Assuming Hubble:
https://www.science.org/doi/10.1126/science.95.2461.212
Legs pulled away:
https://arxiv.org/abs/astro-ph/0203466
Redshift based on physics:
https://core.ac.uk/download/pdf/25323369.pdf
Not to forget e.g.:
https://www.gsjournal.net/Science-Journals/Communications-Gravity/Download/6576
And also simple questions like for example:
Are "spacetime" and "matter" "interwoven": How do objects drift? Which "size relation" would "spacetime" and objects have?
Or: "falls" "matter" "into" "bended" "spacetime" or "bends" "matter" "spacetime"?
Assuming Hubble:
https://www.science.org/doi/10.1126/science.95.2461.212
Legs pulled away:
https://arxiv.org/abs/astro-ph/0203466
Redshift based on physics:
https://core.ac.uk/download/pdf/25323369.pdf
Not to forget e.g.:
https://www.gsjournal.net/Science-Journals/Communications-Gravity/Download/6576
And also simple questions like for example:
Are "spacetime" and "matter" "interwoven": How do objects drift? Which "size relation" would "spacetime" and objects have?
Or: "falls" "matter" "into" "bended" "spacetime" or "bends" "matter" "spacetime"?
I don't waste time on idle speculation stemming from ignorance. Give me the hard Physics from the Professionals any day. 🙂
I have spent a fruitful evening on Einstein's Equation:
Very concise 50 minute talk by Sean Carroll to an interested but not Physics student's audience on Classical Mechanics, starting with Newtonian F=Ma, followed by Special Relativity including E=Mc^2 and Minkowski SpaceTime. And extended into more general non-Euclidian geometries and the surprising predictions of Black Holes when 2GM=r, and more recently, the actual detection of Gravitational Waves and more confirmation of The Big Bang Theory:
Highly recommended. Tensors excellently explained too.
He has a new book out on all this:
https://www.amazon.co.uk/gp/product/B09RX3C3TY/ref=dbs_a_def_rwt_hsch_vapi_tkin_p1_i0
A mere 99p on Kindle. About £11 in paperback. I think that will be my holiday book this year.
I am starting to enjoy this Gravity lark. We now have the instruments to really check it all out.
Other subjects to follow in the following 2 more volumes. 😎
I have spent a fruitful evening on Einstein's Equation:
Very concise 50 minute talk by Sean Carroll to an interested but not Physics student's audience on Classical Mechanics, starting with Newtonian F=Ma, followed by Special Relativity including E=Mc^2 and Minkowski SpaceTime. And extended into more general non-Euclidian geometries and the surprising predictions of Black Holes when 2GM=r, and more recently, the actual detection of Gravitational Waves and more confirmation of The Big Bang Theory:
Highly recommended. Tensors excellently explained too.
He has a new book out on all this:
https://www.amazon.co.uk/gp/product/B09RX3C3TY/ref=dbs_a_def_rwt_hsch_vapi_tkin_p1_i0
A mere 99p on Kindle. About £11 in paperback. I think that will be my holiday book this year.
I am starting to enjoy this Gravity lark. We now have the instruments to really check it all out.
Other subjects to follow in the following 2 more volumes. 😎
I've wondered from time to time if gravity is a result of space pressure gradient, as if masses like planets have a way of condensing space that is around and/or in it, and cause the space most near to it have less spacial pressure. Then as you move away from the planet space begins to become gradually more dense causing masses within the gradient to be pushed toward the planet. That would assume that space is actually something that has a fabric of some sort to it, and that it is not just the absence of anything-ness.
Phil D.
Phil D.
Thanks Steve. A bargain indeed! I shall promptly add it to my Kindle collection before the price goes up.
The trouble is I have a large pile of books, electronic and print, fact and fiction, awaiting my attention.
Instead of wasting my time in this
thread, I should maybe get on with some informative reading!
That's what we need around here, some fresh thinking! 😎
The "fabric" of which you speak is, of course, Dark Matter!
I'm not sure I greatly care about Dark Matter and Dark Energy and Gravity Waves, except that they must doubtless find their way into Einstein's Field Equation.
I have been getting clear what does what in his equation:
The metric tensor can work in any geometry AFAIK, and is good for things like Lorentz transforms in Special Relativity.
The Ricci tensor describes the Curvature of a particular part of 4D Spacetime.
The Energy-Momentum tensor describes the masses or energies or photon momenta that are present, I suppose.
The Curvature Scalar is just a number, a bit like Gaussian Curvature I suppose.
With a particular size and mass/energy Universe, to account for contraction, steady-state or expansion, an extra term called the Cosmological Constant crops up. It's not shown here AFAIK.
The whole thing has been normalised to a speed of light of 1, otherwise the right hand term would be divided by c^4.
As far as I have got... all good stuff, and a Universal Law like F=Ma. In which gravity and acceleration are indistinguisahble by the Equivalence Principle.
Scwarzchild solved it for the stationary or spherically symmetric black hole:
Which apparently surprised Einstein. More surprises with Dark Energy and Dark Matter, but these are particular to our Universe I would think.
Elegant bit of Physics, IMO. 😀
I have been getting clear what does what in his equation:
The metric tensor can work in any geometry AFAIK, and is good for things like Lorentz transforms in Special Relativity.
The Ricci tensor describes the Curvature of a particular part of 4D Spacetime.
The Energy-Momentum tensor describes the masses or energies or photon momenta that are present, I suppose.
The Curvature Scalar is just a number, a bit like Gaussian Curvature I suppose.
With a particular size and mass/energy Universe, to account for contraction, steady-state or expansion, an extra term called the Cosmological Constant crops up. It's not shown here AFAIK.
The whole thing has been normalised to a speed of light of 1, otherwise the right hand term would be divided by c^4.
As far as I have got... all good stuff, and a Universal Law like F=Ma. In which gravity and acceleration are indistinguisahble by the Equivalence Principle.
Scwarzchild solved it for the stationary or spherically symmetric black hole:
Which apparently surprised Einstein. More surprises with Dark Energy and Dark Matter, but these are particular to our Universe I would think.
Elegant bit of Physics, IMO. 😀
"Appeal To Authority" is a Logical Fallacy.
Look, it's all models, models based on empirical observations.. that is you observe something, figure out some way to measure it, then come up with simple model (*) and first make sure it does predict what you originally measured, Then make predictions and hope that those predictions are correct when the predicted events are measured.
But, fundamentally, it's all MODELS.
Do I think we have atoms? I don't know, no clue.
Do I believe we have subatomic particles? I don't know no clue.
Do I believe Newton's "Laws" of Motion are true ( with pico and macro corrections )? Well, we can calculate the trajectory of a cannonball...
But did Newton understand gravity? Nope, he had no real clue about it. But still he didn't need to understand what it was about to do his macro calculations and his models.
BTW, don't be astonished by Black Holes... It's junior level undergrad stuff.
In college I had a bumper sticker on my car: "The Big Bang is an Exploding Myth".
(*) Remember Occam's Razor.
This is, IMHO, the best example....
Mass exerts a force onto the fabric of space (*). think of this as a "weight" onto a "flat, straight" space. The closest to the mass, the more force it puts onto the fabric of space. Object moving along space always move on a straight line ( Newton ) and if space is curved by a mass, they don't know this, they are still moving in a straight line.
This of course is on a multi dimensional fabric of space...
In our Euclidean Geometry we think of space as three dimensional and we have created the concept of "gravity" to account for objects not going on straight lines. This is, just an issue with our using the wrong coordinate systems. Relativity is a start towards describing "curved" space... but ultimately we will, -IMHO- come up with a model that describes NOT gravity but the multi dimensional effects of mass on the fabric of space.
So, gravity is just a tool to measure the effects of mass on the fabric of space. But, if may not exist at all... there might be no "graviton" after all.
I'm also very curious about what kind of creature we'd have to be to experience more than 3D dimensions. THAT will be interesting. Do we need special sensors to detect such? Do we already have them but don't use them?
(*) recall that weight is W( m, g ).. a function of mass and gravity ).
A bit of hard physics, or mathematics: the "Two Body Problem"-)
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Discourse analysis is important.
And also: do the social, emotional, psychological mechanisms allow an open discourse, "science"-?
A great insight into the kindergarten "astrophysics" - exemplary for all society, all discourse, all "science": Redshift - and Halton Arp
https://faculty.humanities.uci.edu/bjbecker/ExploringtheCosmos/lecture20.html
And also: do the social, emotional, psychological mechanisms allow an open discourse, "science"-?
A great insight into the kindergarten "astrophysics" - exemplary for all society, all discourse, all "science": Redshift - and Halton Arp
https://faculty.humanities.uci.edu/bjbecker/ExploringtheCosmos/lecture20.html