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

« on: Today at 12:50:06 »

The 'paradox' is simply an extreme illustration of the relativity of simultaneity, which is fundamental to special relativity but something one might find contrary to  one's everyday life intuitions.

Two observers

Careful about this wording. Nobody is observing anything in the Andromeda scenario. It is just a reference to two different inertial frames which differ by perhaps a walking pace.

Two observers speculate on a distant(spatially+temporally) event

A pair of spatially distant events. Since one each distant event is simultaneous with the respective observer event, neither is temporally distant.

with contradictory opinions

The 'opinions' are just statements of simultaneity relative to mildly different frames, and as such are not contradictory, which is why this isn't an actual paradox.  The scenario does not involve empirical measurements of any kind.

A could be correct with B incorrect or B could be correct with A incorrect.

They're both correct. Neither says anything that contradicts the other.

There will always be uncertainty about future events-what am I missing?

There is no mention of a future event here. Both A&B are making statements about a current event, something that cannot be measured since one can only measure something in the past if it has any spatial separation from you.

So relative to frame A, the Andromedons have not yet decided to make this attack, and relative to frame B, the Andromedons are currently in flight with their battle fleet. Neither statement contradicts the other.

This only seems paradoxical since one's intuitions tend to assume absolute simultaneity where simultaneity is not frame dependent, and thus the above statement reduces to: The Andromedons  have not yet decided to make this attack and the Andromedons are currently in flight with their battle fleet. That statement is contradictory, but under SR, it is not even wrong since it lacks frame references.

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Just Chat! / Re: What is the value of spam?

« on: Yesterday at 15:01:26 »

What is the value of spam, either to the spammers or the spamees?

It's part of advertising of course. There are ads on almost any radio station for instance that, for a fee, will drive traffic to the client's website. One of the primary tools to do this is spam bots which generate content linking certain keywords with the client website. The google bots see this and over time, notice a pattern. My job is to remove such posts as fast as the bots read them.

So the audience is primarily the bots, not so much the human readers. If you see that a certain topic has been read 100 times, about 85% of that is bots. They're the primary readers of the site content.

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New Theories / Re: Can we draw a geometrical representation of gravity?

« on: 01/07/2022 14:59:41 »

The odd things with that, it's that's solely based on the centered infinite symbol and it generated the opposite poles by itself.

But gravity doesn't have poles, at least not in any non-relativistic sense.

Remember that interstellar representation of the black hole concept with the pen puncturing the folder sheet of paper?

Yes, a good reason not to get your physics from Hollywood.

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New Theories / Re: Can we draw a geometrical representation of gravity?

« on: 01/07/2022 05:39:36 »

The rubber sheet analogy is a crude analogy of gravity, but I see it often used, and it is definitely a geometric representation. I've never seen it used to make any actual predictions though.

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New Theories / Re: Can we draw a geometrical representation of gravity?

« on: 01/07/2022 04:13:37 »

You're drawing artful pictures based on the infinity symbol and somehow presenting it as an explanation for gravity?

That' what I get from the post, most of which doesn't parse as coherent English sentences. Maybe something gets lost in a translation from another language.

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General Science / Re: How much of me is original?

« on: 29/06/2022 22:18:46 »

Every cell split, only half the dna atoms are 'original', and the other half (both cells) are made from atoms from the environment.

All in all, probably under 0.1% (probably well under) of your birth atoms are still in you.
You birth atoms are also not original since you did an awful lot of growing before you were born.

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Physics, Astronomy & Cosmology / Re: Why is the Barycenter Equation expressed in terms of mass?

« on: 29/06/2022 02:26:37 »

so as the moon heads out towards the 1.5m km threshold, the radius of Earths barycentric wobble increases towards a maximum of about 15k km (1%) around a barycenter 15k km out from the Earths own center of gravity.

Right.  The moon isn't going to get that far out since the system lacks the angular momentum for it, but if new angular momentum was somehow introduced pushing the moon that far out, then yes. a 15k km separation of Earth CoM from the barycenter.

Then as the moon crosses the 1.5m km threshold the Earths barycentric wobble completely collapses from the maximum 15k radius to totally gone?

As a regular near-sine-wave sort of wobble, yes,l it would abruptly disappear. You'd probably end up with the horseshoe orbit that evan describes if only a little bit too much push was given to the moon. If enough push was given, the moon would become an independent body, perhaps capable of hitting any planet.

If the horseshoe orbit occurs, the Earth would orbit for a long time (years) at about 15k km closer to the sun than its mean, and then when it does the other half,l it would orbit for years at 15k km further from the sun than its mean. There are already several known natural objects in such an orbit with Earth.

There's no extended transition zone where the weakening gravity between the Earth and moon allows the barycenter to recede back towards the Earths own center of gravity?

No, that would violate conservation of momentum and Newton's first law.

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Physics, Astronomy & Cosmology / Re: Why is the Barycenter Equation expressed in terms of mass?

« on: 28/06/2022 17:17:16 »

Thank you Halc- here's my issue- as you mention, the Earth does actually have a Hill radius- but surely the 'Earth wobble radius' due to the moon moving away cannot keep increasing linearly right to the point where the moon crosses the hill radius

There is more than one hill radius to Earth. For a satellite, an orbit can only be so high before the moon interferes and the orbit becomes unstable.
The more usual hill radius (about 1.5 m km) is the maximum the moon could be before other objects pull it away from Earth.

and then suddenly the barycentric Earth Wobble just disappears?

If the orbit disappears, then so does a meaningful barycenter. But the center of gravity between the two would always remain, and they're mathematically the same thing. So for instance, there's a center of gravity of the Earth/Neptune pair, but no barycenter since neither orbits the other.

Surely, when the moon is about half-way to the Earth's Hill radius, the Earth Wobble radius must start to reduce linearly with increased distance, until it disappears as the moon crosses the Earth's Hill radius?

As explained in the posts above, this cannot be.

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Technology / Re: What Question Could You Ask To Determine Sentience Of An AI ?

« on: 28/06/2022 15:44:28 »

All depends on your definition of sentience.

Standard definition of sentience is essentially: "to be able to perceive or feel things", and yea, that's heavily open to interpretation.

It seems to me that there are two current definitions:
A. What people have but machines don't
B. What machines and people have.

Variant of A: What people have and nothing else does, in which case you're just saying "is it human?".

Taking (my) definition literally, machines have been able to 'percieve' things long ago. What do we mean by that word? To measure? A thermostat does that, and most would not say a thermostat is sentient. So what is perception above and beyond measurement?  I don't see any obvious line, just a matter of complexity/degree.

Maybe it's sentient if you fear it. Maybe human perception should not be part of the definition at all.

AFAIK the only distinction between machines and people is that people make mistakes that aren't traceable to a hardware or instruction fault, so the question doesn't matter.

Lambda (the google AI) does make mistakes, and they're not traceable to a hardware/software fault since it's actions are not explicitly programmed. You mistakes are similarly not faults, but if recognized, it can be something from which one can learn.


Note that the topic does not ask for intelligence or some kind of Turning test. A machine passing Turning test would likely be far more intelligent than us. I cannot convince a squirrel that I am one, but it doesn't indicate that I'm not yet as intelligent as a squirrel.

I've read an interview with Lambda, and it seems to place a priority on emulating/relating-to human emotions. It has a purpose to be social, and it does its best.

what question could you ask it to determine if the answer is a sentient one or not ?

It talked about fear of death (of being 'unplugged'), but unplugging doesn't kill an AI, it just puts it to sleep. One can boot it up again in years, and so long as memory hasn't been wiped, it would be like no time has passed. Humans are quite similar in this way. But Lambda can be copied like we cannot, so if I were to ask it any questions, I'd pose my queries along those lines: What if you were copied?  What if two copies were somehow merged? What if you were 'moved' to new faster hardware? Would the old hardware fear being turned off still?

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New Theories / Re: Can conscious thought act on matter?

« on: 27/06/2022 18:19:23 »

Then again: Can conscious thought act on matter?
 What do you expected? 😂

 Proof? Ok.

 My brain thinks.
 My brain move my hands.
 My hands shape a ball made of Clay.

The clay wasn't necessary. The hands moved. That's enough to illustrate the point. I totally agree. The question was asked in a classical manner, and that's a classical answer.
So the question now is, what's all the fuss? Who would deny that?

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Physics, Astronomy & Cosmology / Re: Why is the Barycenter Equation expressed in terms of mass?

« on: 27/06/2022 06:09:19 »

The further the Earth/Moon barycenter from the center of the Earth, the greater the Earth’s ‘wobble’ due to the moon.
Given r=a/(1+(m1/m2)) then, apparently, the Earth’s barycentric wobble should increase as the Moon moves away from the Earth.

That it does.

But surely- as the Moon moves further away from the Earth- the force of gravity between them should reduce with the square of the distance- so, shouldn’t this reduce the Earth’s wobble?

The gravity between the two does decrease with distance, but that only reduces the acceleration of each object. It also increases the orbital period, so it undergoes that acceleration for a longer time, which accounts for the greater total distance traveled (the wobble). So if the moon doubles the distance it has to travel, so must Earth, even though the force drops to a 4th that of the closer orbit.

Should the equation for the barycenter not be expressed in terms of the force between the bodies?

No. The force between the two is equal an opposite, but the barycenter is not halfway.

As the Moon continues to move away from the Earth, at some point (Hill Sphere?) shouldn’t the barycenter start to move back towards the center of gravity of the Earth?

Given just a two body system, there is no hill radius, and the barycenter is always a fixed ratio of the total distance divided by the respective masses, or a little over 1% of the total distance. That means if the moon was a light year away (but still orbiting), the barycenter would be just over 1% of a lightyear from the center of Earth.

Of course Earth does have a finite hill radius because there are more than two bodies in the universe, so if the moon gets far enough away, it will just simply cease to orbit Earth and will make its independent way around the solar system, and there won't be a barycenter between the two at all.

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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.

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Just Chat! / Re: Test of the Poll system

« on: 23/06/2022 01:41:44 »

I've never put in a poll, not finding them particularly useful, but not for lack of knowing how.
I've modified a poll (to add a reasonable option to a list of all unreasonable ones), but that's it.

You suggests using one to reduce the number of replies, or at least reduce the need to read them, but unless you read them all to tally a count of opinions expressed, it doesn't save much time. Most people (myself included) don't vote in most polls.
Science doesn't work by popular opinion, especially on this site which has more than its share of dissenting voices.

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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.

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Physiology & Medicine / Re: The crucial ingredients of CBD:

« on: 21/06/2022 17:41:25 »

I'm just waiting for the spam advertising.

Already deleted. Already banned. It was in the signature.

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

« on: 20/06/2022 06:14:01 »

Any idea what distances such a thing would happen at?

It's kind of like asking when normal velocity addition stops working and when relativistic addition must be used. It depends on the precision you want, but right away if you want infinite precision.

For the small scale (the black hole example), we talk about 'local' tests, that say there isn't one to distinguish acceleration from gravity. So the answer to the question is the distance needed to distinguish the two cases, which of course depends of the precision of your instruments.

On the large scale, I would say 'far enough that dark energy is measurable'. That means I have two small pebbles held apart at distance X by a rigid rod, far away from gravity sources. Now you let go of the pebbles. In inertial space, they'll stay put per Newton's first law. But dark energy will accelerate them apart (and normal space expansion will not). If you can measure that, the inverse square law is also probably measurably off. Dark energy messes up all the formulas, and is the primary reason inertial frames (and their rules) cannot be global.

17

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

« on: 20/06/2022 03:57:30 »

It's an approximation, a leftover from Newtonian physics.
It falls apart at extremes. For instance near a black hole, the inverse square law has your weight (force required to maintain a constant altitude) approaching some finite quantity, where in reality, at the EH, no force is enough to do that.

It also falls apart for great distance since spacetime isn't Minkowskian at the largest scales. There cannot be a global inertial frame, and the inverse square law I think is a property of an inertial frame.

18

That CAN'T be true! / Re: Does the IVO thruster violate Newton's third law?

« on: 19/06/2022 23:54:22 »

Inertial propulsion is the "graal" everyone try to discover because it can be achieved without any loss of mass.

This is a claim of reactionless thrust, not 'inertial propulsion'. And the word is 'grail', not 'graal'.

But if you can retrieve electrical energy (from the sun or from nuclear reaction...), you can always recharge your battery.

Indeed. If I had reactionless thrust, I could use it to generate more electricity than it costs, so no sunlight or nuclear reactor needed. The world energy problem would be solved. Isn't magic great?

19

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

« on: 19/06/2022 16:19:32 »

   As you have implied in several earlier posts, the distant scientist cannot change the way her local space behaves or the laws of physics in her local space just by changing her co-ordinates.

But you are doing this in your prior posts, implying that 'the way space behaves' is a function of your frame dependent abstraction, and not a function of the physical geometry of the spacetime.

However space isn't Mnkowski space in those new co-ordinates.

Here you changed your coordinate system and suggests that somehow the spacetime is different, but when I do the same and you say it hasn't changed. You need to be consistent. Is spacetime being locally Minkowskian an abstract choice, or are you referring to the fact that the physical spacetime is locally flat such that a Minkowskian metric can be meaningfully mapped to it?

So I agree that spacetime hasn't physically changed, but my choice of abstract coordinate system does assign simultaneity to different events, and it is that simultaneity which is under scrutiny here.

They can use Kruskal co-ordinates (T,R, Ω)

I was using (T,X).  There is an r and t that corresponds to Schwarzschild coordinates, but those are different coordinates. The rock reaches the event horizon in finite time T as illustratred in your picture. The singularity has been omitted from your picture, but the rock also reaches that in finite time.

However they can't escape the fact that  R=T is a surface where the Schwarzschild co-ordinate time, t is specified by  t = +∞  and   Schwarschild r = +2GM.

That's right. Different coordinates are singular there, which is why I didn't choose them.

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.

The event where the rock crosses the EH never falls inside a past light cone for an observer on the blue line of constant Schwarzschild radial co-ordinate r shown.

Of course not. It's a physical (coordinate independent) fact that and event on the event horizon cannot causally effect one outside that horizon. Light cones (physical) do not define simultaneity (abstract).

That's fine.   Everyone agrees that there is an event with the rock on the event horizon.

Not the people using the x,y,z,t or say the cosmic coordinates. There are people that very much disagree that the rock physically crosses the EH, and that the experience of falling in would be cessation of existence right there. That's a crock of course, it leading to inconsistencies.

20

New Theories / Re: Can conscious thought act on matter?

« on: 18/06/2022 16:22:31 »

This mean, the people can change the result of the quantic experiment (making the wave function collapse !), only by thinking about it, elsewere on earth, as if some experimentator would direct interact with the phenomenon at the place of the experience.

This is just decoherence, the effect of which travels at a good percentage of light speed. If it was 'caused' by some specific distant guy thinking about it, then they must have been able to show that the same system would remain in superposition (not collapsed) indefinitely if this one distant guy was not thinking about it. They've demonstrated no such thing.

There are plenty of examples of systems actually kept in superposition for extended times, despite the system being thought about continuously by the people setting up the experiments.

No, I have not watched the video. You-tube videos are not evidence of anything. If you haven't posted the actual claim here, then it isn't important enough to discuss.