1

New Theories / Re: If there was one Big Bang event, why not multiple big bangs?

« on: 06/08/2022 04:00:31 »

Olbers's paradox ... says that the darkness of the night sky conflicts with the assumption of a ... static universe.

Well, thermodynamic law also conflicts with the same thing. I don't think this qualifies as a paradox, it is a mere falsification of this 'static universe' suggestion, something that was presumed right through the 18th century.  You sort of propose one yourself, and thus contradict these observations.

2

Physics, Astronomy & Cosmology / Re: How many levels of orbit can a planetary system sustain?

« on: 31/07/2022 22:57:33 »

The ratio can be far less than that.  Charon orbits Pluto, and its mass is a whopping 12% of the primary.

Mathematically, there seems to be no limit to the number of levels for at least reasonable stability. True stability cannot be achieved in any 3+-body system.

One can add levels to the other side as well, say by having our sun orbit some larger star well away from our local solar system, but it needs to be quite far away to not disturb the orbits of the more distant things. So best way to get a lot of levels is to not have a lot of separate things (planets) orbiting any one thing.

3

New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 17/07/2022 12:48:30 »

Quote
Sorry, why do you claim that my assertions are wrong.

Because they predict the rapid breakup of arms

Wow!!!
You fully that our scientists "predict the rapid breakup of arms"

Halc clearly had stated that our scientists "predict the rapid breakup of arm":

predict the rapid breakup of arms

That prediction is a direct outcome from the Dark matter.

You did not answer the questions I required. You thus fail the test of being someone who displays any reading comprehension skills. For instance, this little quote above suddenly suggests that I said that scientists predict the rapid breakup of arms, when I of course made no mention of scientists (or dark matter) in what you quoted. It was your assertions that do, and thus your assertions that contradict the evidence.

Can you please explain the process how the dark matter by itself can help the spiral arms to be recovered to their nice symmetrical spiral shape after they have been broken?

Another example. Nobody every suggested this. You cannot read.

Based on the replies here, and since you would not answer the questions testing if it is worth leaving the topic open, it is (and has been for some time) very apparent that communication with you is not possible. This is a waste of everybody's time. Topic closed.

4

New Theories / Re: What is the real meaning of the most-distant-quasar/galaxy?

« on: 15/07/2022 17:35:18 »

I have also said that trying to explain something to you is about as productive as explaining it to my cat.
You display negligible reading comprehension skills, and mathematics and logic skills are also lacking.

This topic seems to be devolving into assertions of slander against these 'astonomers' that have so little clue, so I am once again threatening to close the topic that has long since passed any hope of making progress.
But let me put a little reading comprehension test, based on some past responses. Apologies for treating you like an 8 year old in a quiz here, but you're determined to act like one.

What is being violated without dark matter is basic Newtonian law. We have objects (our solar system say) that accelerate far more than can be accounted for by the sum of the forces applied by all the various baryonic masses in the galaxy. Thus there must either be more (a lot more) mass that isn't baryonic, or Newton's laws (the inverse square one concerning gravitational attraction) are wrong.

Your explanation is valid as long as we ignore the arms.

What exactly do you think I was saying in that quote?
Please don't just copy my words. Tell me in your own words what the post was about.
You don't have to agree with the words, just give an indication the comprehension isn't totally absent.
Why do you think mention of arms was necessary?
Who was the comment addressed to?
What was the purpose of my posting that when I've been mostly keeping out of this?
Was the purpose served?

You go on to reference the same comment again, like it somehow backs some assertion of yours.

There is no "arm" in [Halc's same] explanation.
In order to get better understanding, please also see the following:
https://en.wikipedia.org/wiki/Galaxy_rotation_curve
"The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's center."

The rotation curve comment you quote also does not mention 'arms'. What do you think the wiki comment says? Why was a reference to my comment (especially my lack of mention of 'arms') relevant to this comment?

Quote from: Dave Lev on 08/07/2022 06:22:55
Please set each star at a fixed velocity and fixed orbital radius.
Based on my basic logic, while a star at 15KPC complete only one galactic cycle, a star at the same arm at 3KPC would have to set 5 orbital cycles.
So please, based on your superior logic, how many orbital cycles (for the one at 15KPC) are needed in order to break the spiral arm structure?

Here you actually make a point. Stars closer to the center go around much more often than the ones further out. The ratio of 5 is poor mathematics, but the ratio is not far from that. You're giving evidence that your assertions are wrong. Not sure why you're doing this.
As for superior logic, you commit a straw man fallacy here, asserting facts that are not held by these 'clueless' astronomers, only by you. So that's the demonstration of 'superior logic' you've been requesting.

As you think that you do understand, then please advice what is the meaning of the following message:
https://scitechdaily.com/galactic-bar-paradox-a-mysterious-and-long-standing-cosmic-conundrum-resolved-in-cosmic-dance/
"The bar in the center and the spiral arms are thought to rotate at different speeds. If they are disconnected the bar shows its true and smaller structure (left). Every time they meet, the bar appears longer and its rotation slower (right). Credit: T. Hilmi / University of Surrey"

OK, since you quoted that, what do you think it says? This is a reading comprehension test remember.
Why do you think this comment is relevant here?
The comment is a caption, and is obviously commenting on the images above it. What is it saying that you think is worthy of being introduced in this topic?


If this is too difficult, you've really no business wasting all our time on this site.

5

Physics, Astronomy & Cosmology / Re: What would happen to the Solar System's gravitational connections if ....?

« on: 14/07/2022 20:30:13 »

while, on a occasion, a comet does crash into the Sun, the newly formed Black hole would be an extremely small target to hit.

So the Sun turning into a BH would affect the orbit of a comet but not (as @Halc  says) that of the planets?

No, it would not alter the orbit of a comet or any other object. The sun squashed down to a 3 km black hole merely becomes a much smaller target, so a comet that might have hit the sun would miss the black hole.

6

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

« on: 05/07/2022 16:02:05 »

Halc, I would argue that the two participants have contradictory positions: one says the decision has not been made yet and the other says the fleet is in transit already.

Yes,l those statements are contradictory, but neither of them says those things. Both statements presume absolute simultaneity by their omission of frame references, and it can easily be shown that neither postulate of special relativity can be true if the premise of absolute simultaneity (an intuitive assumption) is taken.

Part of the confusion is the statement of something not measured: 'The Andromedons are considering whether to attack' for instance is not something that anybody has measured. It is simply an abstract statement, a description of the scenario in question by the narrator so to speak. No observer can measure this, certainly not A and B. Likewise, if Andromedons are somehow considering an attack on Earth, it isn't against humans since there's no way they could have yet measured a species yet to have evolved. We are no more fact to an Andromedon obesrver than they are fact to us.

7

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

« on: 05/07/2022 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.

8

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

« on: 04/07/2022 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.

9

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.

10

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.

11

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.

12

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?

13

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?

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: 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.

16

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.

17

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

« on: 14/06/2022 21:52:56 »

If you throw a rock into* a black hole does it's mass parameter ever increase?   (does it "get bigger"?)
*into --->  perhaps I should have said towards the black hole, it hasn't actually gone in yet.

This mass parameter is frame dependent, but from your distant viewpoint, the mass/energy it gains from KE is balanced by the PE mass/energy lost from it being at an ever lower potential. So no. A 1 kg rock dropped into a black hole increases the BH mass by 1 kg.

If there is somebody falling in locally with the rock who is in possession of some kind of mass-measuring device, the rock won't change mass along the way. This is a very different frame, but same answer.

So how do black holes get bigger - other than through black hole mergers?

Relative to a distant frame, they grow. A rock never falls into a Schwarzschild black hole, but a BH with a rock dropping into it doesn't conform to the Schwarzschild metric. I'm unfamiliar with the name of a metric describing a mass falling in. Surely somebody must have worked it out.

Your implication that black holes can grow only through mergers suggests that none exist, since it takes two to make one. I do think there are absolutists that suggest the non-existence of black holes since they very much do contradict descriptions in absolute terms.  In order to do this, I think they must suggest that matter stuck on the 'surface' of nothing must actually move outward despite lack of force pushing it that way. Not sure if the people who actually know their physics are on board with that. I've never seen a formal absolutist theory presented as a replacement for GR.
Violation of conservation of baryon number is also a contradiction with such a theory.

18

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

« on: 14/06/2022 18:54:34 »

Something must be holding light back faster than light itself travels.

Nothing 'holds back' anything. Relative to anything inside a black hole, all future events are also inside. Trying to send light 'outside' is like trying to shine a light onto 2021 from here. Light doesn't travel into the past no matter how hard you attempt it.

I understand gravitational waves propagating outside the black hole

Gravitational waves generated outside the black hole propage outward, yes.

so it's the propagation of internal gravity waves that stops light ?

They have nothing to do with it. Gravitational waves are just another thing that moves at light speed, but also do not move into the past.

does light even exist inside a black hole ?

Of course. If you jump into a big one with a set of lights (say in a room full of glow sticks), you'd not notice anything different as you crossed the event horizon. Light from the glow sticks would still reach you from every direction.

What ,then, is the effect of changes to the distribution of mass inside a BH?  Anything?   Do we know?

Per the no-hair theorem, there is zero external effect of changes to internal mass distribution. Nobody outside could measure it.
A black hole has externally measurable (total) mass, angular momentum, and charge. That's it.

19

Plant Sciences, Zoology & Evolution / Re: What are your favourite Plant Pictures?

« on: 14/06/2022 17:41:07 »

Agree. I edited the post to embed the picture right in the post rather than just have it appear as a small downloadable thumbnail at the bottom. That shot deserved more.

20

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

« on: 14/06/2022 17:38:15 »

Is gravity...travelling then ?

Gravity is not something that travels. It is a distortion of spacetime.
What does travel is gravitational waves, which carry information about the changes to the field. A Schwarzschild black hole doesn't emit any gravitational waves because it isn't changing, but say two black holes orbiting each other emit an incredible amount of energy in the form of gravitational waves. These are generated outside the black holes and travel at light speed.

Changes to masses inside a black hole emit gravitational waves that cannot leave the black hole for the same reason light cannot.