1

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 11/12/2024 17:16:13 »

Two people pass each other on the street; and according to one of the two people

This is a nit, I know, but this sort of language has set public understanding of modern science back by decades since the wording seems to suggests that physical reality is dependent on human observation, which is true of neither relativity nor quantum mechanics. That rant said, keep in mind that "according to one of the two people" is a misleading shorthand for "relative to the inertial frame in which one of the two people is stationary".

Humans choose different frames all the time, and not often that one except when checking one's pockets or something.

Secondly, another nit is that using special relativity presumes flat spacetime, and the spacetime between here and Andromeda is not flat.  I'm also willing to ignore that since it is besides the point being illustrated by the example.

an Andromedean space fleet has already set off on its journey,

Third nit is that this statement is a counterfactual, a statement of the state of something unmeasured. Such assumptions are typically assumed in special relativity exercises, but not in quantum mechanics where few consider the principle to be sound.  I am fine with this assumption for this exercise.

None of these nits are fatal to the point, or make it wrong.  Yet.

How can there still be some uncertainty as to the outcome of that decision?

Exactly because it has not been measured. That leaves it uncertain to the measurer, and in fact it will never be measured because by the time the light gets here, the telescopes will long since have ceased to function.

But Penrose assumes both a 3D spatial universe (presentism) and a 4D spacetime universe, and the paradox seems to revolve around these two incompatible models being used at the same time.
In the 4D block model, the entire history of the universe has the same ontology, meaning the invasion is objective fact and is not in any way a function of a reference frame. Presentism is not compatible with relativity of simultaneity. Simultaneity across the universe is objective and not observer or frame dependent. He needs to pick one model and stick with it. This is more than just a nit. It crosses the line into being self-inconsistent.

If to either person the decision has already been made, then surely there cannot be any uncertainty.

Under the block model, all events have equal ontology and the decision very much is part of it. The only thing that the two observers are doing is comparing different pairs of objective events. There is no 'has already been' of anything since that is a reference to the present.

according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past.

Here is a blatant reference to presentism, something totally incompatible with the 4D spacetime model his two people are leveraging. Thus Penrose sows the seeds of confusion rather than adding clarification to what SR actually says. Bad form...

So many many light years away, the "paradox" of Andromedeans having launched, or who will launch, a fleet, is well beyond an observational limit.

The observational limit is one's past light cone, and that cone is identical for both observers (well, a couple meters apart actually), but way over at Andromeda, those two different light cones are still only a couple meters apart.


A more correct wording of the Andromeda scenario is that we have these two different inertial frames differing by a couple m/sec in velocity, and we have one event of these two people passing by each other, and another event of the Andromedan fleet launching. Relative to one of those frames, the people passing event occurs first, and relative to the other frame, the fleet launch event occurs first.  Same two events, but ordered differently in one frame as compared to the other. That is a far better wording of the scenario that presumes SR and it utilizes only B-series language.

2

Just Chat! / Re: Help!

« on: 10/12/2024 16:10:06 »

I tried to reply to Hamdani on his "origin of the magnetic field" and it came up as a new topic which I find I cannot delete. Any suggestions?

I fixed it. Not deleted. It is now a reply to that topic.
As for why it occurred, no idea.  Wrong button pushed?  The topic title was different ("field" instead of "force"), so that means it was never composed as a reply in the first place, and suggests the post wasn't opened via the 'quote selected' option.

3

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 07/12/2024 18:53:02 »

I was hoping we could lean towards what an exact reason for the different ages of twins is.

Am I missing something? I was of the opinion that this question was comprehensively answered at an early stage in this query.

That was indeed done in the very first reply, the important part being this:

There are many ways to explain the difference, so there is no one correct way.

That means that anything claiming or asking for 'the correct way' is already presuming something wrong.

The rest of the post lists only one of the ways to explain it, and also provides counterexamples to every one of the 'explanations' mentioned in the videos, both of which were shown to be mistaken in subsequent posts. Takeaway is to use a peer reviewed text to get your information, not pop videos, even those put out by supposedly knowledgeable celebrities.  An arm-chair amateur like me should not so easily be able to find the mistakes in them.

If you want another explanation, it can be something as simple as "That's the nature of Minkowskian geometry". A straight (timelike) path between two spacetime points (events) is longer in length than one that isn't straight. This is unintuitive since in Euclidean geometry, the opposite is true.

4

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 29/11/2024 00:26:06 »

. Having never used supposed "AI"(no intention of doing so-you can't teach an old dog new tricks!), I am in a weak position to criticise. I have seen some atrocious rubbish in replies to questions posed by others and a high degree of suggestibility. In response to a question that requires a blunt "NO", answers will often digress into unsubstantiated speculation with the seeming aim of perpetuating the discourse rather than delivering a straightforward answer.

This is very perceptive.  Yes, the answers always seem agreeable, and if you protest a correct answer by asserting your own sufficiently plausible rubbish, none of the LLMs seem capable of telling you that it's still rubbish. It might seem a bit skeptical, but it will encourage you to explore your line of thinking rather than point out where it contradicts evidence or contradicts itself.

I didn't want to tell copilot that its answers were rubbish. I had hoped that it would figure it out itself after I pointed out inconsistencies in its replies.

We may not need forum moderators in the future, an LLM can analyse and critque the work produced by the forum users LLM well enough.

Moderators are needed to moderate, to recognize and deal with posts not complying with the rules. Being correct is more of a job for site experts, be they moderators or not.
I'm no expert in pretty much any subject, but I know enough to take apart a lot of answers I see from AI.

(I copied and pasted the reply @Halc obtained from Gemini).....   

Actually, Hamdani provided replies from both chatGPT and gemini. I just copied his quotes so I could color them

My replies below are replies to chatGPT apparently agreeing with much of what gemini had to say..

You say that "spacetime is curved due to the acceleration" in an accelerated frame..... It would be better to mention that acceleration causes the perception of curvature, or locally mimics gravitational effects due to the equivalence principle.

But that isn't right. There is no curvature locally, so there cannot be any local perception of it. In the non-local case, most of the effects are due to the accelerated frame. it is quite hard to distinguish curved spacetime from flat since all the effects are present in both, but differently.
For instance, I am under proper acceleration of 1g and dangle a clock on a long rope. In both cases the clock on the rope will run objectively slower, so that effect is not due to curved spacetime. But the two cases differ a bit for how much slower since they differ. Nearby, it differs but a little, but for a gravitational field of a small mass, it can differ a lot over not that much distance.

The equivalence principle does not suggest any of this

In an accelerating reference frame, spacetime itself doesn?t curve in the same way...

It doesn't curve at all. Spacetime curvature is objective, not a coordinate effect, and an accelerated frame is just a coordinate choice. I would have immediately grilled gemini on this point, but I have no access to it.

students using LLM to write the essays and someone else using a LLM to mark and grade them.

They get what they deserve if they commit the same sins. Education should devolve into GIGO. Nobody should pay for any pseudo-education implemented in this manner.


I talked to my AI about black holes and got Newtonian answers in response. It had no clue.
Thought of another one: Sagnac effect is a favorite empirical disproof of anything Einstein.  Let me have a go:


Does light travel west faster than it does east?

Light travels at a constant speed in a vacuum, ... This speed remains the same regardless of the direction in which the light is traveling, be it west, east, or any other direction.

The notion that light could travel faster in one direction over another doesn't hold up according to our current understanding of physics. The speed of light is influenced by the medium through which it travels (such as air, water, or glass), but not by the direction.

So if I create a vacuum tunnel and some mirrors around the world and shine a pulse in both directions, both pulses will return to the origin spot at the same time?

Yes, exactly! In your vacuum tunnel setup, if you shine a pulse of light in both the west and east directions simultaneously, both pulses would return to the origin at the same time. The speed of light in a vacuum is constant and does not depend on the direction of travel.

This constancy of the speed of light is a cornerstone of Einstein's theory of relativity and is true regardless of the motion of the source or the observer. It?s one of the fascinating and sometimes counterintuitive aspects of the way our universe works.

So the Sagnac effect disproves relativity then? It predicts that west and east light go different speeds and measurement of this difference is used to detect absolute rotation. Sure, most Sagnac devices have a far smaller circumference than a planet, but the principle is the same

...The Sagnac effect occurs in rotating reference frames, such as a rotating disk or the surface of a spinning planet like Earth. In these scenarios, if you send two beams of light in opposite directions around a loop, they will take different amounts of time to complete the loop.

So the two pulses do take different times to come back to the emitter then?

Yes, in the context of the Sagnac effect within a rotating reference frame, the two pulses of light would indeed take different amounts of time to return to the emitter.

Not in the context of Sagnac. In the context of what actually happens

Let's break this down in the context of what actually happens with light pulses and rotation.

If you set up a vacuum tunnel with mirrors and shine a pulse of light in both the westward and eastward directions, the two pulses would indeed take different amounts of time to return to the origin if the system is rotating.

So I didn't color anything, but it didn't take much to get it to contradict itself. The LLM did not take into account the rotating frame of reference in the first reply because despite the real-Earth scenario, I didn't word the question in a way that drew attention to the fact that we're working with a rotating frame, despite the fact that west and east are not even defined on a planet that doesn't rotate.

I did word the one query as an attempt to discredit relativity like so much training material attempts to do, and it at least didn't take that bait. I partly wanted to see if I could lead it down a false path if it looked like it was my purpose to do so.

The copilot replies were edited heavily, cutting it down to actual replies, and cutting out all the educational stuff it tried to add on, and of course all the congratulatory stuff at the end about how perceptive my questions are. It tacks that on to ever single reply in some form or other.

5

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 27/11/2024 19:09:27 »

Asking chatbots about relativity is almost always going to get wrong answers.
I can highlight the wrong and particularly correct and really wrong answers.

Is GR needed for accelerated frames of reference?

Yes, General Relativity (GR) is necessary when dealing with accelerated frames of reference, especially when the acceleration is significant or when gravitational effects are involved. While Special Relativity (SR) handles inertial frames (non-accelerating), GR extends the theory to include non-inertial frames, such as those that are accelerating or influenced by gravity.

In GR, gravity is not seen as a force but rather as the curvature of spacetime, and this curvature affects how objects move, including those in accelerated reference frames.  So, for understanding the full effects of acceleration, particularly in the presence of strong gravitational fields, GR is required.

ChatGPT tries to sneak in gravity since yes, GR is needed to deal with gravity. But acceleration does not produce gravity at it implies. It seems to just repeat this comment a number of times.


At least ChatGPT doesn't attempt to leverage the equivalence principle, which I cannot say for the other examples.  Gemini is definitely the worst of the bunch.

The same question for Gemini,

Yes, General Relativity (GR) is crucial for understanding accelerated frames of reference. Here's why:
 * Equivalence Principle: GR postulates that gravity and acceleration are equivalent. This means that an observer in a uniformly accelerating spaceship cannot distinguish between the force of acceleration and the force of gravity. This principle forms the foundation of GR.
 * Curvature of Spacetime: In GR, gravity is described as a curvature of spacetime. This curvature is caused by the presence of mass or energy. In an accelerated frame of reference the spacetime is curved due to the acceleration.
 * Time Dilation and Length Contraction: GR predicts that time runs slower in a gravitational field or an accelerated frame of reference. This is known as gravitational time dilation. Additionally, objects appear shorter in the direction of motion in an accelerated frame, a phenomenon called length contraction.
 * Global Positioning System (GPS): GR is essential for the accurate functioning of GPS satellites. The satellites are moving at high speeds and are at a different gravitational potential compared to Earth's surface. Without accounting for GR, the GPS system would be significantly inaccurate.
In summary, GR provides a comprehensive framework for understanding the physics of accelerated frames of reference. It is a fundamental theory that has been experimentally verified and is essential for many modern technologies.

That was horrible. I would love to have questioned Gemini after that comment and show how it directly contradicts itself.  I tried to do it with copilot, getting this conversation, not as bad as the two above. This is actually my first intentional interaction with any LLM ever.

Is GR needed for accelerated frames of reference?

In some ways, yes. Accelerated frames of reference are closely tied to the principles of General Relativity (GR). Unlike Special Relativity, which deals with constant velocities and inertial frames, General Relativity accounts for acceleration and gravity.

Einstein's theory of General Relativity generalizes the idea of relativity to include non-inertial (accelerated) frames of reference. It essentially states that the presence of mass and energy curves spacetime, which in turn affects the motion of objects. In this context, acceleration can be considered equivalent to gravitational effects?a principle known as the equivalence principle.

So, while you might not need all the complexities of GR for simple cases of acceleration, understanding the full implications of accelerated frames and gravityindeed requires the framework provided by General Relativity. If you're diving deeper into areas like gravitational waves, black holes, or cosmology, GR becomes essential.

Try as I might, I cannot get copilot to mention accelerated frames without dragging gravity into it as well, making the comments ambiguous.

But there is no curve spacetime under special relativity. Are you saying that acceleration creates spacetime curvature?

You're correct that Special Relativity (SR) doesn't involve curved spacetime. SR deals with inertial frames of reference?those moving at constant speeds relative to each other?and doesn?t account for acceleration or gravitational effects.

Note the evasion of actually answering the question.

In General Relativity (GR), however, acceleration and gravity are indeed linked to the curvature of spacetime. The equivalence principle in GR states that locally (in a small region of spacetime), the effects of acceleration are indistinguishable from the effects of gravity. This means that in an accelerated frame of reference, the spacetime can be thought of as curved. So, yes, acceleration is related to spacetime curvature in the context of GR.

Think of it this way: in an accelerating elevator, you feel a force pushing you down, similar to gravity. GR explains this by suggesting that the acceleration causes a curvature in spacetime, akin to how a massive object like Earth curves spacetime, creating what we perceive as gravity.

What do you mean by acceleration being linked to curved spacetime? Does it curve spacetime or not? The equivalence principle indeed says that locally, the effects of acceleration are indistinguishable from gravity, but locally, spacetime is not curved, gravity or otherwise. You seem to imply otherwise when saying "This means that in an accelerated frame of reference, the spacetime can be thought of as curved" when the opposite is true, that locally, even under gravity, spacetime can be thought of (and is) flat.

You bring up an excellent point. You're right?locally, spacetime is considered flat, even in the presence of gravity. Let's clear up the confusion.

The equivalence principle states that within a sufficiently small region of spacetime, the effects of acceleration are indistinguishable from the effects of gravity. In this local sense, spacetime can be approximated as flat, which aligns with your statement that locally spacetime is not curved.

To clarify: acceleration itself does not directly cause spacetime curvature. Instead, in GR, acceleration and gravity are related through the equivalence principle. When we consider larger scales or longer durations, gravity (or the presence of mass and energy) causes spacetime to curve. This curvature affects how objects move, leading to what we perceive as gravitational effects.

So, while an accelerated frame of reference might feel similar to experiencing gravity, this does not imply that acceleration curves spacetime in the same way mass and energy do. Locally, spacetime remains flat, and the equivalence principle helps us understand why the effects of acceleration can mimic gravitational effects in small regions.

There was more, but you get the idea

6

Physics, Astronomy & Cosmology / Re: Has anyone heard of tresino theory?

« on: 14/11/2024 21:57:16 »

A tresino is apparently quite stable, and its discovery (a 5th phase of matter, one beyond the 4th:plasma) seems to have implications on all sorts of things unexplained until now, including why the corona of a star gets so much (100's of times) hotter that the surface of the star, and why planets take so long to cool down.

I don't see how a particle can be a phase of matter at all, but apparently this 5th phase involves some proportion of tresinos, like plasma involves nuclei stripped of their electrons, thus destroying their identity as 'atoms'.

It is theorized that tresinos were a common state of matter early in the universe, but no 'very' early since it took many epochs for things like protons to form in the first place.

Apparently cold fusion, not understood well at first, may finally be explained by properties of the tresino. It isn't fusion, but it may still well be a viable energy source. Much to learn first.

7

Physics, Astronomy & Cosmology / Re: Is it Just Hadrons that The Large Hadron Collider...collides ?

« on: 29/10/2024 19:27:09 »

What is so special about Hadrons ?

They're made of smaller things.

Are there other particles on the menu to be collided too ?

For the most part, no. Electrons for instance are not thus accelerated, although it seems capable of it.

How do they store the particles ?....are they kept in a test tube or something ?

Everything is made of them, so it is simply a matter of isolating them (from Hydrogen say) and then sending em down the pipe.

How many particles are fired at one time ?

Hundreds of billions (of protons, which are hadrons) per beam, and multiple beams.  I've heard a thousand times that figure, so not sure if there are thousands of beams or they can make some beams more dense.

8

Physics, Astronomy & Cosmology / Re: Are Atoms Perpetual Motion Machines ?

« on: 29/10/2024 18:12:28 »

Where does the energy come from ?

It was always there since the atom was made.

2: Does this make atoms (et al) Perpetual Motion Machines ?

No. A PMM is something from which indefinite work can be extracted, at however small a rate. One cannot extract indefinite energy from the motion of an atom.

9

Physiology & Medicine / Re: What Happens To White Cells After They Have Dealt With An Infection ?

« on: 29/10/2024 17:15:32 »

Blood cells (of any type) are fairly short lived, so the white cell counts go down by attrition and lack of many more being produced after their need is gone.  The counts return to normal levels around 5-25 days after infection is cleared, depending on the sort of infection involved.

Red cells might live 4 months. White cells have a life expectancy of only a few days, so if you stop making them in abnormal quantities, their numbers quickly decrease to normal levels.

I have given a unit of red blood cells, and that has the longest wait time before I'm allowed to donate again. Giving whole blood, plasma, platelets, all have shorter wait times.
I've not heard of giving white cells, but I know that early in the covid days before the vaccines came out, whole blood from a person who had recently gotten over a covid infection was in serious demand to serve as a treatment for the more dire cases.

10

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:31:59 »

but the principal job of a non-playing conductor is to moderate the balance between sections more subtly than the dim and cresc markings on the score, and to add interest by varying the tempo and accent.

Not during performance I hope. This moderation (interpretation of the composer's dream) is done at rehearsal and hopefully not significantly changed in performance. There is also something to be said about changing it up when something is performed night after night, as opposed to school performances that tend to occur 1-3 times at best.


And Alan, love the anecdotes.

11

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:29:24 »

To be honest, if our conductor made an impromptu change in something just on the night when a piece was being performed, then a lot of us would have missed it and played the thing as we did in rehearsals anyway.

It would seem terrible if any alteration was made without rehearsal. Yes, it's during rehearsal that he's most needed, but also most ignored because until the music is more familiar, concentration is mostly on the paper and less on the peripherally visible conductor..

We had a school band piece where you play the first half, then the 2nd which starts with one of those attacks after a long pause between the halves, then the first again exactly the same. In concert (a competition), our conductor was quite nervous and got to the end of the first half and mistaken thought he had finished, putting the baton down. We're all waiting for the attack signal. Of maybe 80 of us, I think I heard two small toots. The rest of us were watching and very confused. The band leader picked up on our distress immediately and resumed, but it wasn't supposed to go that way.

12

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:21:50 »

Halc, I am going to dispute, most likely out of ignorance!, something you said. You suggested that after a long pause or a sustained note it is entirely not clear when the attack of the next note is supposed to be. Surely if one has a good sense of time(something I lack) coupled with the sheet music, one has a pretty good idea?

They've practiced, so yes, but a pretty good idea doesn't get everyone on the attack simultaneously, and there's no beat to follow through say a fermata.

In a choir, our was small enough to lack a conductor, so heads turned to the organist and head nods. You get this piece with a loud long final note that needs an abrupt cutoff. All of us are looking at the organist (well to the side, hard to see from the rear, or down in a pit, invisible to the audience) for the head nod. It sounds terrible if the voices don't cut off as one.

13

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 27/10/2024 17:53:22 »

It's to keep everybody in sync. If you're in one corner of the band/orchestra, you might not be able to hear all the others, and one group can get devastatingly out of sync with others. We ran into this marching in Mexico city, 6 wide down a 2 lane road. A car was parked, blocking one lane, forcing 3 columns to go and the other three to follow. This spit the drums and made it so those in the rear could not see the conductor (the drum major up front with the super tall stick).  We got measures out of sync and it was a disaster. Those who heard both sides just stopped playing.

Anyway, imagine a classical piece with a dramatic pause or long held note. It is entirely not clear when the attack of the next note is supposed to be. The conductor makes this explicit, and everybody should be watching for it.

Small groups (jazz ensembles, barbershop quartet, etc) don't need one, but usually one of the players visible to all uses head/instrument motion to fill the role.

14

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 17/10/2024 17:00:23 »

I had been told years ago by a theoretical physicist(who now holds a distinguished position at an American university but who will remain nameless) that GR was needed for accelerated frames of reference.

That's actually pretty sad for somebody claiming those credentials.  I googled "is GR needed for accelerated reference frames" and got correct replies from several sources with poorer credentials, but one from a university site.

AI overview: "No, general relativity (GR) is not required for accelerated reference frames:

    Special relativity (SR) is sufficient
    SR can handle accelerated frames and objects, and is sufficient to explain the Twin Paradox. SR is valid in the presence of accelerations because it describes flat Minkowski spacetime"

That is a very poor reference (as is any LLM), but it's correct.  The twin paradox bit is barely relevant since discussion of it is rarely described via changing accelerated reference frames.  That quote seems to answer more "Is GR needed to describe acceleration" rather than to describe accelerated frames, but accelerating objects are perfectly well described in inertial, accelerating, expanding, rotating, and other kinds of frames.

The next hit is better, from University of California, Riverside
"It's a common misconception that special relativity cannot handle accelerating objects or accelerating reference frames. Sometimes it's claimed that general relativity is required for these situations, the reason being given that special relativity only applies to inertial frames. This is not true."

I got no immediate hits that said that GR was required, but I'm sure they're out there. Bottom line is, GR is needed for curved spacetime, which only comes into play with gravity and dark energy, and none of the discussion here has been about those things.  I do not know my GR well enough to say do the tensor calculus required to generate numeric answers. Tensor mathematics is not required for anything in SR, including Rindler frames.

"What is the exact cause of the time dilation of the twin?"
The same thing that causes time.
And I'm not sure we actually know what that is.

I don't think time is something that is caused.  It is exactly like asking what causes distance, which seems to be an ill-posed question.  I do agree that most of the recent discussion has digressed from the immediate topic title, but since it is mostly framed as questions about relativity and not assertions of speculations, I've not moved any of it to the lighter side.

15

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 17/10/2024 14:10:29 »

Is the bold statement backed up by experimental evidence?

I don't think they've ever made a set of gears with a 1000-1 size ratio, let alone turn any reasonably rigid object at significant relativistic speeds.  The bolded statement  is backed by the very simple mathematics of γ=1/√(1-v²) which is identical on both sides since the sole variable v is identical on both sides.

If an identical measuring tape is glued to the ship, will the earth observer see two of those tick marks go by every second?

The situation is not symmetrical since the ship is accelerating and the Earth is not.  Earth can have a tape measure of indefinite length attached to it, one that the ship can read forever.  The ship (at proper acceleration of 1G) can trail not even a light year of tape behind it.  The tape cannot extend beyond the ship's event horizon without breaking.

How many ticks per second the Earth observer sees depends on when he looks.  At some point, the ticks go by infinitely fast just before the tape ends, and then they see no more.
There was that ship event where the ship guy sees 2 ticks/sec go by.  In Earth frame, the event there that is simultaneous with that ship event, the tape will already have been exhausted.

I made the mistake of trying to apply SR to a scenario where some of the frames of reference were not inertial and were thus in need of GR for solution.

GR is only needed for situations involving gravity (which I suppose my black hole mention does).  But the accelerating frame of the ship is a straight SR exercise.  You might want to look up Rindler frame or Rindler coordinates for info on how SR treats an accelerating frame like this.

SR handles accelerating frames just fine, as it does rotating frames. It handles normal expanding frames as well, but not accelerating expansion frames which involves dark energy and puts things into GR territory.

16

Physics, Astronomy & Cosmology / Re: What is the optimum speed to make a point in space disappear?

« on: 16/10/2024 16:48:22 »

I read-read that and I did come across kind of snarky. Apologies for that.

In the example in the other thread where the spacecraft was travelling at 2c relative to the tape measure you said the earth would be hardly receding at all and that it would not reach 1 light year with unlimited time of travel of the craft.

Right, but it has nothing to do with speed, but rather continuous proper acceleration.  The greater the proper acceleration, the closer the event horizon is to the ship, and Earth will never fall through the event horizon, but will instead remain close (in the accelerating frame of the ship) and forever visible, just like a lantern dropped into a black hole.
Of course quantum mechanics says that at some point the last photon to reach you will leave Earth, so looking at it from a quantum viewpoint, Earth will remain visible only until that last photon reaches you, but the 'never disappear' statement presumes continuous light, not quantum.

So there must be a speed at which the earth appears to recede the fastest

No, there's no such speed, especially since ship speed reaches any arbitrary value regardless of rate of acceleration. First of all, the appearance of velocity is dependent on one's choice of frame type.  Secondly, for all constant levels of acceleration and relative to said accelerating frame, Earth will 'appear' to drop away slowly at first, pick up speed as the ship velocity relative to Earth grows, and then slow as Earth approaches the ship's event horizon.  It will never appear to cross that horizon.

For linear non-accelerating travel, that is limited to c, and in flat spacetime, Earth will always be visible.  In real spacetime, at any ship speed, the ship will eventually cross Earth's event horizon, but both Earth and ship will always be able to see each other.  There is no way to exit the visible universe.  Despite recession velocities > 3c relative to the cosmic frame, new stars become visible (enter the visible universe) every day, and none of the ones visible ever vanish from sight (unless they cease emitting light).

17

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 15/10/2024 22:26:22 »

ISS is orbiting the earth, thus it's accelerating. But your accelerometer won't show the correct value of acceleration there. It will show something close to zero g.

Read my post.  Any accelerometer shows proper acceleration and an orbiting satellite will undergo no proper acceleration. The acceleration you speak of is coordinate acceleration, and even that might be zero. I mean, in the coordinate frame of my house, my orbiting sat-TV satellite is stationary (no coordinate acceleration) which is why I can point my dish at it and not have to move the dish.

Does it mean I will see the earth recedes with speed 2c? What happens to the cosmic speed limit?

With respect to #70: yes the earth will appear to recede at 2c because your rapidity will be 2c. From the earth you will be seen to be travelling at <c.

There's no direct appearance to a recession speed.  It is very frame dependent.
Relative to the inertial frame in which the ship is momentarily stationary, the Earth will be receding at around 0.964c.  Nothing can exceed c relative to an inertial frame. But if there was a tape measure glued to Earth that goes all the way along your journey, with a tick mark every light second, you'd see two of those tick marks go by your ship every second. That's what it means to be moving at a proper velocity of 2c relative to Earth.

Relative to the ship's accelerating frame, Earth will be seen receding almost not at all, and will never reach a light year away even after indefinite ship time, all very much like dropping a clock into a black hole.

Celerity (and not rapidity) is another word for proper velocity, at least they're the same in Minkowskian spaceitme.  One must be careful to use the correct term in other contexts.  And yes, the >c recession of galaxies relative to the expanding cosmic frame (not an inertial frame) is like a celerity of sorts. The proper distance between us and the distant thing (measured along a line of constant cosmologtical time) grows at a rate of >c.  Inertial frames are not even relevant at such distances, but if you remove all energy, the distant galaxy would not be moving faster than c relative to any inertial frame since the distance would not be along a line of constant cosmological time. It would be far closer, and its velocity in that frame would be sub-luminal.  It would still be moving at well over c in the non-inertial expanding frame, but that's a coordinate difference, not a physical one.

Accelerating a clock alters its tick rate

Not true.  I gave examples early in this topic that demonstrates otherwise, bottom of post 20.

18

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 02/10/2024 16:50:54 »

Oh dear, here we go, again. Word salad.

Indeed.  The prior posts have been removed for several reasons.

1) Nonsense in the main sections of the forum
2) Contained personal information
3) Had nothing to do with the topic title, hence is a hijack of a topic
4) Contained a bibliography which was nowhere referenced
5) Contained no content from any of said bibliography
6) Word salad as Paul points out
7) Duplicate posts

At least the first three of those violate forum rules.

19

New Theories / Re: Gravity In Relative Motion - is there any solution?

« on: 28/09/2024 02:51:02 »

So does it mean that kinetic energy starts to be added to the inertial mass/energy of a body only when a certain velocity is reached?

No.  It would violate energy conservation if I did work on an object and no energy was transferred to it because it wasn't yet moving fast enough. This again is not unique to relativity theory.

If total relative velocity of our (me and the object in question) motion is equal to 0,99c - how can we know how our velocities are distributed in other frames?

The relative velocity addition formula can do the frame transforms for velocity.  Lorentz transforms are for coordinate transformations between frames.

Is there any difference between me incoming towards the object at 0,99c and object incoming towards me at 0,99c?

Yes.  The vector of one velocity is the opposite of the other.  Different objects are stationary in the two respective frames.

And what if in some other frame we (me and object) are incoming at each other with equal speed? Where the additional mass/energy will be added?

Each object contributes its own kinetic energy in that frame.

[/quote]And coming back to ISS and your answer - can you help me finding the fragment of text telling that relativistic mass becomes a 'thing' only at extremely high velocities and that it's effect is completely non existent below some specific velocity?[/quote]It doesn't have a minimum speed. It's a thing at any speed (even zero), but not very significant at low speeds where classical approximations are sufficient to express the KE of the object (E=mv?).

And if not that - should I understand that classical mechanics might lead to effects that are contradictory to effects of SR?

Classical mechanics is a good approximation at low speeds. Neither classical nor relativistic mechanics says that objects gain no kinetic energy until some minimum speed is reached.

So until some particular value adding velocity allows escaping gravity but then and then just like that - "Flop!" - and now adding velocity will start increasing gravitational pull?

Yet again, this is totally wrong. Stop asserting this.

Nope. [Einstein is] completely and utterly wrong about it. There's only 'as much' energy, that 'fits' into a given amount of mass (matter).

Only so much in stationary matter. There's no limit to KE, else again, energy conservation would be violated.

You simply can't get more energy from a given amount of matter than energy released due to annihilation - in which mass is literally turned into photons and stops existing as matter.

A fast moving small thing emits more energy (higher energy radiation) in such an annihilation. There's no limit to it. You seem to be in continuous denial of a simple theory, rather than taking the position of trying to learn about what you don't want to accept. You cannot falsify a theory that you refuse to attempt to understand.  I see little point in responding to somebody so closed to learning.

Your chosen quotes from wiki do not contradict this, except in their using the word mass to mean relativistic mass, which is an unconventional usage of the term.

20

New Theories / Re: Gravity In Relative Motion - is there any solution?

« on: 27/09/2024 23:38:45 »

I can defend relativty

1. there's a definitive & limited amount of energy in matter (according to Einstein it's unlimited) - equal to (half of) energy released to matter-antimatter annihilation.

Einstein is right. There is no limit to how much say kinetic energy one can give to a given object.  One can always apply a force on it to make it go faster, assuming one can find an energy source to do so.  So in the frame say some neutrino, the small bunny in my front yard perhaps has more energy than one stationary anti-bunny.

2. Body moving at 100% c

A 'body' has mass and cannot move at c, as Paul has pointed out. This is really basic stuff that shows you apparently know nothing about relativity theory.

gravitational attraction decreases gradually as source-object accelerates from 0 to 100%c

Gravitational attraction isn't a function of acceleration. Not one bit.

Because I really despise making theoretical calculations with real-life units like (kilo)grams, meters or seconds, I made myself a simplified system of units based on constant c (moving 1 space unit in 1 time unit).

They're called natural units, and in such a system, c=1 and can be treated as such in all equations.  But you assign c=10, which isn't a natural unit.

let me show you an example:
https://en.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic_vs._rest_mass

Relativistic mass has been depricated since about 70 years ago.  By definition, mass is proper mass, and is frame invariant.  What varies from one frame to the next is momentum.  This is not a change in theory (The original SR paper did not treat mass as proper mass), but rather a standardization of convention.  Nevertheless, the idea of relativistic mass has an incredible presence on the internet, which is why chat bots use it so much.

Gravity is not a function of mass in relativity theory. It is a function of stress energy, which is frame invariant.

Basically according to Einstein there's no limit to the energy for any amount of mass (matter) - you can pack infinite amount of Giga-Joules into a single proton (or electron).

Or negative even. Potential energy is negative and there's no limit to the depth of a hole you can drop a proton into.

Well, sorry but in  my uneducated opinion, matter/antimatter annihilation turns WHOLE mass into energy and there's ALWAYS a finite & measurable amount of it released

Because you started with finite energy. Einstein doesn't say you can get more energy from a stationary thing. It has to be moving fast to have more energy than the stationary one.  If it's fast enough, you can do more work with it than the anti-matter thing, and it doesn't even have to disappear to do it.

and it's theoretically IMPOSSIBLE to get any more energy from matter.

So this assertion is clearly wrong.

Thing is, that for some reason physicists keep thinking that mass has a definitive amount energy at rest (inertial frame) but then you can 'pack it' with potential and kinetic energy to infinity.

If it has KE, it isn't at rest is it?  If it has PE, that is negative.  There's a limit to how close to zero PE can get, but it isn't really defined where zero is. I.E. there's not a place you can be that is free from gravitational potential.

Let's take a theoretical comet/asteroid entering edge of Earth's atmosphere at a relatively small (flat) angle - question: Will making the asteroid/comet faster increase or decrease the chance of it hitting Earth?

Bunch of problems with the pic:  The comet cannot be a comet since it is moving too slow. It is clearly in eccentric orbit about Earth, while comets orbit the sun and move much faster relative to Earth when in its proximity.
The tail of the comet points the wrong way. It should extend to the right, not down where you drew it. A comet tail is not a wake, despite all the popular images depicting it that way.

That aside, if the comet takes the same initial trajectory but is moving only a tad faster, it will have less time to accelerate to the right as you depict. It will miss. This is basic Newtonian mechanics and all of this has squat to do with relativity theory.

In Einstein's model increasing speed = increasing energy = increasing mass what should lead to stronger gravitational attraction

This is completely wrong. Relativity theory says no such thing. Mass is not a function of speed. Gravity is not a function of mass, at least not directly.
Please do not say what Einstein's model predicts if you don't know how (and when) to apply the model. It is a straw man fallacy.

My model predicts something directly opposite - the faster the comet moves, the less it is attracted to Earth

This is also wrong. Yes, it will miss, but because of what Newton says, not because the attraction is less.

What Einstein's model is suggesting is that the faster the interplanetary bearing ball will be moving in relation to Earth (stripped out of the atmosphere), the stronger it will be attracted to the surface - and that a slower cosmic bearing ball has bigger chance of escaping Earth gravity.

Totally wrong. Relativity theory says no such thing.

Ok, here's question to those willing to stand in defense of Einstein's model - let's have 2 bodies of equal mass accelerated simultaneously at the same rate to relativistic velocities - so that both are moving at the same speed next to each other (appear stationary to each other)

Gravity isn't a function of acceleration.  So you're saying that you still have two objects that remain relatively stationary.  Gravity between them (in their own frame) will be unaffected per the first postulate of SR.

- will the increased velocity of those objects (observed in some other frame) have any effect on gravitational interactions between those accelerated bodies or they won't observe any difference?

In a frame in which the two objects are moving fast, the two objects will accelerate towards each other more slowly.  Less acceleration, not more like you describe.  It will take more time for them to collide than they would in a frame where their mutual center of mass was stationary.  In a frame where they're moving at 0.866c, they'll take twice as long to collide with each other.

I'm pretty sure (like 85-90%) that not even the most loyal supporters of Einstein's model  can tell with >50% certainty what the model actually predicts - and if some actually can make such prediction, it will most likely go against predictions of some other Einstein supporters...

The validity of a model has nothing to do with a vote of support. Plenty of people support relativity without understanding it. Some support alternative theories, and a small fraction of those understand both Einstein's theory and their own choice.  Supports relativity does not imply that one can make correct predictions.

As for myself - I literally have no idea what Einstein's Relativity tells us about such/similar scenario

You're sure making an awful lot of incorrect assertions about it for somebody who admits a lack of understanding.

So ok, one more 'scenario' - what would happen with ISS if SuperMan or some other OmniMan would simply stop it's motion around Earth?

Hope they take their time about it.  The ISS is delicate and does not take kindly to large forces being applied to a small area.  Irrelevant, I know.  We assume it is sturdy for this exercise.  We assume Superman can exert reactionless force, but only because it doesn't change the answer.

Let's say it would stop moving right above my house and then would be left 'hanging there' not moving in relation to surface (at least horizontally) - what would happen then with it?

Nothing to do with Einstein.  It would fall somewhat to the east of your house after around 5 minutes.  East is due to Coriolis force.
If the object has sufficient altitude, it won't hit Earth at all. If it has even more altitude, it won't even lose altitude, which is how geosync satellites manage to stay put despite not moving in relation to surface.

Now, in this case I can at least try figuring out what Einstein's model predict in similar situation..I'd say that according to Einstein, ISS would simply keep 'hovering' there endlessly or maybe even it would slowly 'drift away' from Earth.

Seriously, you thing Einstein would suggest that??  This is pretty hard evidence of crackpottery.

Why I'd say so? Well, since it stopped moving in relation to Earth's surface, it's energy decreased and so did the gravitational pull towards Earth - that's how I'd see Einstein's model..

A stopped thing still has mass, which is non-zero energy. Surely you don't think otherwise. OK, it seems you do...
If you want us to take your posts seriously, take seriously the thing with which you disagree.

What my model predicts however, is that I'd have at best 10 minutes to move most important stuff from my house before couple hundreds (thousands?) tons of 'space junk' would turn it into a landing pod (although 'falling pod' seems to fit better) - it would simply start falling down from it's orbit like 2 seconds after it's motion would stop...

1) half that time  2) it will miss  3) it starts falling right away (just as it is doing now), not after 2 seconds.


I cannot quote the copilot answer since it isn't text, but almost everything in it is completely wrong, and is a fine example of why it is terrible to ask any chatbot questions on theories about which it has no actual understanding.