1

New Theories / Re: What makes Riemann's Hypothesis Hard to Prove?

« on: 23/07/2022 23:53:27 »

the thing about Mathematics:   It often looks easy when you know how to do it

I have heard that the mathematician Gauss had a reputation for working on a mathematical problem until he solved it. And then, knowing it was true, he looked for the most elegant way of showing that it was true - but in a way that made it difficult for other mathematicians to use the learnings he had gained in discovering the result.
https://mathworld.wolfram.com/NonconstructiveProof.html

2

Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 12/07/2022 14:44:35 »

Eternal student, I hope your family are ok. Covid seems to be very erratic in terms of symptoms and severity of illness, even for the vaccinated. I assume I had it(big assumption) as I did not bother doing an antigen test this time. What led to this assumption is that I got a collection of signs and symptoms very similar to the vaccine (Pfizer) side effects, which I have never got from viral infections before. It was however very mild overall. Wishing a quick recovery for all.

3

Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 11/07/2022 13:32:47 »

Eternal student, i'm sure our resident philosopher alancalverd,  has plenty of conundrums and paradoxes to stimulate your analytic skills. Hope he doesn't blacklist me for this suggestion!!

4

Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 10/07/2022 22:53:42 »

Hi.

[Quote from: alancalverd on Today at 00:50:18}
And why doesn't the new stuff contain even older rocks fossils and artifacts than the old stuff it has buried?

    I always assumed it did but we don't take enough care not to destroy the fossils and artifacts.
[/quote]

Not just us, but all the stuff that lies on top of trilobites and dinosaurs, and has done for millions of years. If stuff was being recycled from lower layers, you'd expect to find significant  anachronisms (e.g. trilobites above dinosaurs).

But all the evidence suggests - or at least is interpreted as - that new stuff just arrives from space and settles on the ground!

5

Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 10/07/2022 06:29:58 »

The underlying hypothesis is that old stuff gets buried by new stuff. But that new stuff must have come out of the ground from somewhere else. So where are the holes from which came the stuff that buried the ice age?

Do the holes include volcanic craters?
The overall even distribution in rural areas suggests a source bigger and more general than dug up.
Towns and cities certainly and there are a lot of water filled gravel pits around and old quarries. I think Portland is now smaller than it was. Where I used to live there was a lot of open cast mining, after extraction it was resurfaced and is now lower than it was.
It would be an interesting study to see if the sources could be traced and added up.

6

Just Chat! / Re: It's too quiet: I'm seeking a recommendation for a thread to read.

« on: 10/07/2022 00:43:05 »

You might have more fun by asking a question that interests you. Threads tend either to end quickly with a statement of fact, or to degenerate over time into a ritual exchange of grenades between entrenched positions, but a fresh question can provoke some good thinking and writing for a few days.

7

Physics, Astronomy & Cosmology / Re: Why can't i understand the andromeda paradox?

« on: 08/07/2022 12:43:11 »

Eternal student, all is clear this morning though I don't feel 100% yet. It's simply two participants(halc won't allow observers-he's correct) in different frames disagreeing on the timing of an event. My malfunctioning engineering brain viewed the two frames as being sufficiently similar as to consider them equivalent. A higher speed of one participant would give a greater slope to your green line. The wording in the wiki article(penrose's version) still 'hurts' my brain. Many thanks again.

8

General Science / Re: A-Z Of Anything Or Anyone Associated With SCIENCE!!

« on: 06/07/2022 16:08:25 »

The mineraloid opal is amorphous SiO2·nH2O, hydrated silicon dioxide.The water content is usually between three and ten percent, but can be as high as 20%.Opal ranges from clear through white, gray, red, yellow, green, shore, blue, magenta, brown, and black.

Of these hues, red and black are the most rare and dear, whereas white and green are the most common; these are a function of growth size into the red and infrared wavelengths see precious opal.Common opal is truly amorphous, but precious opal does have a structural element.

9

Physics, Astronomy & Cosmology / Re: Why can't i understand the andromeda paradox?

« on: 05/07/2022 17:08:38 »

 

as far as Brenda is concerned, when she passed Paul and said "Hi!"  the invasion from Andromeda has been launched.   Meanwhile, for Paul the meeting to decide whether to invade Earth or not hasn't finished yet.

When did you become a Downing Street spokesman? 

10

Physics, Astronomy & Cosmology / Re: Why can't i understand the andromeda paradox?

« on: 05/07/2022 16:24:22 »

Thank you, eternal student, for your detailed reply. I can follow your reasoning explicitly, however I can't grasp the concept, if that makes any sense. Bottom line: I think I have covid too. I had sudden onset low back pain and brain is not in gear and i'm making mistakes in everything I do. I will return in a few days(hopefully).ps i'm fully "vaxxed" as the conspiracy theorists would call it.

11

New Theories / Re: Origin of magnetic force

« on: 02/07/2022 12:05:27 »

I seem to have CoVid

Get well soon.

12

Just Chat! / Re: Are The Naked Scientists Listeners open to interviews?

« on: 29/06/2022 18:22:50 »

Hey,

I just wanted to share the abstract of my finished thesis here:

This study explores the crossroads between science, personified by experts, and sound media, including their listeners: How do recent science radio broadcasts and podcasts aim to establish interaction between experts and the listening public through their rhetoric, format and affordances? The aim is to understand the roles specialists and citizens enact within the shows and society.
The theoretical framework approaches the programmes with three variables: a rhetorical analysis of their audio and platform content to uncover the linguistic aims, an analysis of their format and in-show interactions to understand the division of responsibilities, and a study of both programmes' affordances to listeners and experts to reveal the possibilities and impossibilities for interaction.
The analysis compares a BBC radio show with an independent podcast by an MIT lecturer and researcher: The Naked Scientists (TNS) and the Lex Fridman Podcast (LFP). The sources stem from a selection of seven pairs of episodes with matching topics. In addition, this thesis builds on an analysis of 8 interviews conducted with active and non-active listeners. The selection of the BBC show permits a contextualisation through BBC guidelines and regulations.
The findings reveal a fundamental challenge that drives the interaction between experts and the public. Sound media shows are confronted with the dilemma of making scientific knowledge accessible while sharing the complex confrontations essential for scientific progress. They express their approaches to the problem through different goals, communication tools and roles for their guests, listeners and hosts. LFP decides to share the challenges within scientific fields and engage listeners with the fundamental questions but has to accept that the broad public has difficulties accessing its content. TNS informs and actively involves its audience with easily accessible content. However, it does not prepare its listeners for disagreements, ambiguities or contradictions within science.

I have also attached my full thesis, in case anybody is interested in having a look!

Many thanks!

13

Physics, Astronomy & Cosmology / Re: What is a black hole made of?

« on: 28/06/2022 02:01:10 »

I have read that black holes might be viewed not as objects at all but  as extreme spacetime  curvature 

Is that correct or have I perhaps  misconstrued?

14

Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 26/06/2022 02:58:44 »

Suppose it was something else like Beta particles being emitted isotropically by the source.   Why would that not follow the 1/r2 law for the bombardment intensity received on the surface of a sphere held at a constant metric distance (a radius) r from the source?

Presuming you didn't do anything funny like put detector/source at different potentials, the inverse square law would work given this constant r (say both held at opposite ends of a stick).  Space expansion would make no difference. Dark energy probably would, but that counts as 'something funny' just like gravity does. Dark energy would put tension on the stick. Space expansion would not.

If we assume that the particles are traveling at (say) c/10, then there will be an event horizon beyond which these particles will not pass, because space will be expanding faster than c/10 by the time they got there.

OK, but if distant detector is held at constant distance from this emitter, it will cross over that 'event horizon' (towards us) and the particles will get to it.

What you're talking about isn't the event horizon, it's the Hubble radius, the distance where Hubble's law yields c. The event horizon is a little further away from that, and it has to do with acceleration, and is not a function of the current expansion rate like the Hubble radius is.  So a beta particle moving at 0.1c would get at most a 10th of the way to the Hubble radius, and would take an infinite time to do so.

This event horizon will be much smaller than the event horizon for light (which defines the limits of our observable universe).

The light event horizon is about 16 BLY away. Current radius of the visible universe is about thrice that, so they're very different things. The latter is all the material in the universe which at some past time might have had a causal impact on a given event (Earth, here, now).  The event horizon is the comoving distance of the nearest current event from which light can never reach here in any amount of time.

After all, the size of our observable universe is not at a fixed distance - it expands at the speed of c.

The Hubble sphere expands at c (by definition). The visible universe expands at somewhat over 3c, which is why we can see galaxies that are currently about 32 BLY away (comoving distance).  The event horizon is barely expanding at all.

so (in principle) there are distant galaxies that people on Earth could see today, but
 which will not be visible in 10 billion years

Hate to disagree, but new galaxies become visible over time. The most distant ones were not visible several billion years ago, even if one used the best telescopes. Yes, the galaxies cross beyond the event horizon, but that doesn't mean we can't see them any more than we stop seeing somebody falling into a black hole.

The inverse square law is about the intensity received at a distance, r, from the source.   That is a physical distance, so it is determined by the metric.   It is not determined by reference to a difference in the values assigned to locations in the co-ordinate system we commonly use to describe an expanding universe.

Just so, yes.

The usual co-ordinates used in an expanding universe are the called the co-moving co-ordinates.  Galaxy 1 can have fixed co-moving co-ordinates and it's tempting to say it has a fixed position.   Galaxy 2 can also have fixed co-ordinates and we can be tempted to say it has a fixed position.

Right. The rate that a given galaxy changes its coordinates is called peculiar velocity, and the peculiar velocity of almost all objects is quite low, a few percent of c at best.

If you posit some particle that travelled at c/10 (and didn't slow down)

In an expanding metric, the paricle will slow down without some force maintaining its peculiar velocity. Newton's laws only work in a static metric.

15

Physics, Astronomy & Cosmology / Re: Why is inflation needed in the bbt?

« on: 25/06/2022 19:34:09 »

An other point of view.

PS1 :: National Conference on CICAHEP, Dibrugarh (2015), 01, 94 – 99
Horizon, homogeneity and flatness problems – do their resolutions really
depend upon inflation?
Ashok K. Singal
Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad-380 009, Gujarat, India
asingal@prl.res.in; COS3, Poster, CICAHEP15.169.1
In textbooks and review articles on modern cosmology [1, 2, 3, 4, 5, 6] one almost invariably comes across a
section devoted to the subject of observed homogeneity and near-flatness of the universe, where it is argued that
to explain these observations inflation is almost a must. In fact that was the prime motive of Guth [7] to propose
inflation in the first place. We show that the arguments offered therein are not proper. The horizon problem, which
leads to the causality arguments, arises only in the world models where homogeneity and isotropy (cosmological
principle) is presumed to begin with. We do not know whether the horizon problem would still arise in non-
homogeneous world models. Therefore as long as we are investigating consequences of the cosmological models
based on Robertson-Walker line element, there is no homogeneity issue.
We also show that the flatness problem, as it is posed, is not even falsifiable.


The usual argument used in literature
is that the present density of the universe is very close (within an order of magnitude) to the critical density value.
From this one infers that the universe must be flat since otherwise in past at 10−35 second (near the epoch of
inflation) there will be extremely low departures of density from the critical density value (i.e., differing from
unity by a fraction of order ∼ 10−53), requiring a sort of fine tuning. Actually we show that even if the present
value of the density parameter (in terms of the critical density value) were very different, still at 10−35 second it
would in any case differ from unity by a fraction of order ∼ 10−53. For instance, even if had an almost empty
universe, with say, ρo ∼ 10−56 gm/cc or so (with density parameter Ωo ∼ 10−28, having a mass equivalent to
that of Earth alone to fill the whole universe), we still get the same numbers for the density parameter at the epoch
of inflation. So such a fine-tuning does not discriminate between various world models and a use of fine tuning
argument amounts to a priori rejection of all models with k 6 = 0, because inflation or no inflation, the density
parameter in all Friedmann-Robertson-Walker (FRW) world models gets arbitrarily close to unity as we approach
the epoch of the big bang. That way, without even bothering to measure the actual density, we could use any
sufficiently early epoch and use “extreme fine-tuning” arguments to rule out all non-flat models. Thus without
casting any whatsoever aspersions on the inflationary theories, we point out that one cannot use these type of
arguments, viz. homogeneity and flatness, in support of inflation.

https://s3.cern.ch/inspire-prod-files-c/cf01320a84f09089fdb2318c01fc440b

16

Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 25/06/2022 10:08:47 »

The reasoning about Event Horizons is almost backward.

I was not thinking about a horizon at a fixed distance.
- After all, the size of our observable universe is not at a fixed distance - it expands at the speed of c.
- But space can expand faster than c, so (in principle) there are distant galaxies that people on Earth could see today, but
 which will not be visible in 10 billion years, because the expansion of space has carried them outside our visible universe.
- If you posit some particle that travelled at c/10 (and didn't slow down), there would be regions of our visible universe that could never detect these particles, because the space in between is/will be expanding faster than c/10.

Usual disclaimer: Ignoring intergalactic medium, electrostatic forces, magnetic fields, etc which will change the velocity and/or direction of real beta particles.

17

Physics, Astronomy & Cosmology / Re: Is the inverse square law only approximately correct in general relativity?

« on: 24/06/2022 22:52:52 »

Suppose it was something else like Beta particles being emitted isotropically by the source.

If we assume that the particles are traveling at (say) c/10, then there will be an event horizon beyond which these particles will not pass, because space will be expanding faster than c/10 by the time they got there.
- This event horizon will be much smaller than the event horizon for light (which defines the limits of our observable universe).

18

Physics, Astronomy & Cosmology / Re: Why is inflation needed in the bbt?

« on: 24/06/2022 13:54:26 »

This should help:  https://wmap.gsfc.nasa.gov/universe/bb_cosmo_infl.html#:~:text=The%20Inflation%20Theory%20proposes%20a,relatively%20gradually%20throughout%20its%20history.

19

Just Chat! / Re: Test of the Poll system

« on: 22/06/2022 23:44:38 »

I do now...

20

Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 22/06/2022 02:00:15 »

Space and the way things behave in space follows the physical laws of science.   Changing co-ordinates can't change that.

Agree, but this contradicts what you said before. I had needed (and got) some clarification before knowing which one was the contradictory one. It concerns your alternate metric with T  =  x + t.

Consider dropping a scientist and well stocked lab into some arbitrary place and time in the Universe. 
...
Specifically, they can choose to use some arbitrary co-ordinates but they will know and can tell that the metric isn't Minkowski in those co-ordinates - it it will only take them a few experiments to determine that.

This suggests that the 'way things behave in space' can be changed by a coordinate change. They're apparently performing experiments to empirically demonstrate an abstraction (their alternate choice). No experiment will show that, because as you say, the choice of abstraction can't change the way things physically (empirically) behave. One can tell the metric isn't Minkowskian simply with a pencil and paper. The experiments will all be unaltered by the choice.

We seem to have a fundamental disagreement about the line between arbitrary abstraction and objective (and classical) physical fact.

However, some co-ordinate systems make things seem unnatural when expressed in those co-ordinates.   E.g. Objects move around in circles in some some co-ordinates but physically they are always obeying Newton's laws, it's just that the chosen co-ordinates don't describe an inertial frame.

Newton's laws are local simplifications and what might be a natural coordinate system for local description will be inevitably entirely unnatural for one's larger purpose. Yet again, we're not discussing local physics here, so choosing a nice neat local CS is inappropriate (not a natural choice). Most of your post focused on this 'LIF', but the 'L' there makes it unnatural for a non-'L' description unless spacetime remains effectively flat between observer and measured event, which in this scenario is not at all the case.  Your scientist with the well stocked lab isn't considering anything in the lab, and he isn't even taking any actual measurements. The question wasn't 'what will the distant observer measure?'.

That Schwarzschild time, t, isn't unimportant or arbitrary to the scientist.  That co-ordinate t is what they will experience as local time (if they hold still).

This is wrong. How does one 'experience' any kind of abstract time?  One experiences proper time. That's the only time that's physical. One does not 'experience' the time for some worldline not in one's presence.

     There's no disagreement here.  The original sentence had the phrase "if they hold still" in it and the distant scientist is located on a surface of constant radial co-ordinate r, their entire worldline is on that surface.   For the distant scientist, the proper time interval they experience (between two events in their worldline) = the difference in the Schwarzschild co-ordinate time, t, between those two events.[/quote]OK, I see what you mean. The same could be said worldline a meter above the event horizon, despite the objective massive dilation of the lower time relative to the distant time.
Yes, in answering 'when does the rock cross the EH?', I was using time T (not t) to express the simultaneity since T is not singular. It may take some arithmetic, but one can very much compute distant-observer-t from a given T, even if T isn't something the guy's clock on the wall measures.

As shown on the Kruskal diagram (which was produced in paintbrush and took what seemed like hours before you criticize it again for not showing irrelevant details like the singularity).

Fantastic job then. I never managed reasonable curves with the primitive tools I have. I'd have just grabbed one from the web.

Anyway, the event with the rock crossing over the EH is never in the past light cone of the distant scientist

Of course not. It wouldn't be an EH if it was.

  So that event never causes an effect for the distant scientist.

None claimed.

This is getting to the crux of matter:   We orbit around Sagittarius-A* which seems to be a big black hole, so we are that distant scientist, following a worldline that lies (more or less) at constant Schwarzschild radius r.   Is it possible for that black hole to engulf a rock and grow, so that it's mass parameter is now larger, during a finite amount of time for us scientists?

Hard to say, since the question is abstract, not physical. Your scientist might pick a metric that is singular at the EH, but that metric cannot actually describe the situation. The LIF doesn't work when there's gravity involved at all. The Schwarzschild metric doesn't work in anything but a static black hole. Even the distant orbiting thing violates that if it has any mass.
So I think I discussed this before. Absent a metric describing an infalling mass, one has to simply approximate and imagine it, possibly giving wrong answers. More below, but your comments are on point.

Will the mass parameter of Sgr-A ever change in my lifetime?

If it didn't, it wouldn't have a mass parameter in the first place. Based on that alone, you have only two choices, a singular infalling metric that either allows mass at all, or one that doesn't. The rock (and everything else in its history) goes in or it doesn't. Keep in mind that the question isn't physical. It is strictly an abstract one unless one asserts physicality to a particular abstraction.

(Assuming that I do not ever get off planet earth and do something like travel fast or travel toward the black hole etc).   It makes little practical difference if the gravity we experience from the centre of the galaxy is always caused by a black hole of Mass parameter M plus a small rock close to the event horizon with mass m,   or if eventually we just experience the gravity from a Black hole with mass parameter M+m.

A black hole with no mass at all, but a lot of crap almost in it is (must be) empirically indistinguishable from a black hole of mass <a lot of crap>. Thus we will very much experience M+m because m is there, inside or not. What we experience isn't abstract.

However, there is a small difference, one is symmetric, the other is not.

Yes!  That's a huge problem with plan B above (it all stuck on the surface).  Suppose we start with a solar mass black hole (about 3km).  Now we take a concrete cylinder 100m in diameter and massing 100 stars. It's a super-long cylinder. We jam that thing into the small black hole and it all sticks to the non-rotating surface in one place. That puts all the mass off to one side, not centered at all. That would violate the whole no-hair thing. The black hole (after the bar thrown in) is still stationary in the frame of the system CoM, (which is nowhere near where the small black hole was at first). Where is the mass? All on the one side, or centered on the radius?  It can't be the former since an off-center mass would be empirically detectable, not just an abstraction. Right?  No? My logical seems a little naive/Newtonian, so maybe I'm just doing the mathematics wrong.

So maybe a tiny mass gets stuck, but the next tiny mass (on the same side??) grows the EH, swallowing the first. You drop in a big rock, and all but the trailing bit gets in, at least relative to this chosen metric.