1

Physics, Astronomy & Cosmology / Re: Are there different types of gravity?

« on: 08/09/2018 20:14:04 »

It's tricky Bill. Einstein didn't consider it a geometry, as far as I get it,. He used calculus and thought of gravity and inertia in those terms. the geometric interpretation was something that came without him, not meaning that he didn't see the implications, just that he found it questionable. " he thought that General Relativity was no more and no less geometrical than Maxwells theory of electromagnetism; and that the important achievement of GR was the advancement of the unification programme in direct continuation of special relativistic electrodynamics. Einstein thought that the special theory unified electricity and magnetism, the general theory inertia and gravity. Yet, we shall see that, unbeknown to most scholars, Einstein was emphatic in his belief that this should not be interpreted as a ‘geometrization’of gravity, especially if ‘geometrization’was seen as a reduction of gravity/inertia to spacetime geometry

.... As early as 1926 Einstein insisted, explicitly, that his work should not be understood as reducing physics to geometry, either his work on GR or his (and Weyl's and Eddington's) work on a unified field theory of gravitation and electromagnetism. Interestingly, what seems to be Einstein's first clear statement on the matter was prompted by a letter from Hans Reichenbach. Reichenbach was at the time engaging with Weyl's and Eddington's theories, and wrote Einstein that he thought that seeing electricity as geometrical in Weyl's theory is not more than an illustration (Veranschaulichung), one that, he argued, is equally possible (and equally trivial) in GR. Einstein agreed wholeheartedly, writing ' You are completely right. It is wrong to think that ‘geometrization’ is something essential. It is only a kind of crutch (Eselsbrücke) for the finding of numerical laws. Whether one links ‘geometrical’ intuitions with a theory is a … private matter. '   "

So when speaking about a geodesic it's not a geometric path in his terms, " Already in the first papers in which Einstein starts making use of the metric tensor to give an account of gravitation, he is at pains to establish the status of the geodesic equation as describing the motion of particles as “straight and uniform” (geradlinig und gleichförmig) even when subject to gravity. This would lead him to call the geodesic equation a “generalized law of inertia”; redefining inertial paths such that the category includes motion under the influence of gravity. ..... Already in a note added in proof to Einstein (1912), Einstein had stated that equation (1) gives the equation of motion of point particles “not subject to external forces”.

Thus, it was clear that already in 1912, before even embarking on a metric theory of gravitation, Einstein thought of (static) gravitational fields not as invariant force fields diverting particles from inertial motion. Already, in 1912, he thought of equation (1) as describing inertial motion on one hand, and as describing motion in the presence of (static) gravitational fields on the other. "

"  Einstein effectively states that the very distinction between ‘gravity’ and ‘inertia’ is useful only for relating the theory to its predecessor theories; it is not a distinction from within the theory itself. Put differently, if one just looks at the theory without relating it to predecessor theories, there is no need whatsoever to distinguish ‘inertial terms’ and ‘gravitational terms’ in the geodesic equation. "

By that I understand he meaning that talking about gravity as a force directing the inertia (willingness to keep on indefinitely) of a test particle made little sense to him.

"  In Einstein's mind, the unification was very similar indeed, as the December 1919/January 1920 text on the development of relativity shows. There, he recalls the magnet-conductor thought experiment described in the first paragraph of his 1905 paper on special relativity, from which he concludes. ' The existence of the electric field is a relative one, depending on the state of motion of the coordinate system used; only the electric and magnetic field together can be attributed a kind of objective reality, independent of the state of motion of the observer, i.e. of the coordinate system. '

Einstein then describes how he worked on a review article of special relativity in 1907, and links the above realisation regarding the electric and magnetic field to another thought experiment regarding inertia and gravity: ' Then I had the most fortunate thought of my life in the following form: The gravitational field only has a relative existence in a manner similar to the electric field generated by electro-magnetic induction. Because for an observer in free fall from the roof of a house, there is during the fall — at least in his immediate vicinity — no gravitational field. Namely, if the observer lets go of any bodies, they remain, relative to him, in a state of rest or uniform motion, independent of their special chemical or physical nature '

quotes taken from " Why Einstein did not believe that General Relativity geometrizes gravity " By Dennis Lehmkuhl.

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Physics, Astronomy & Cosmology / Re: Are there any ways to show whether nature is fundamentally continuous/discrete?

« on: 05/09/2018 22:35:52 »

No.Spacetime is a mathematical concept used to model the observed universe, and for the most part it works best as a continuum. It's easy to plot discrete events on a continuum, but very difficult to do so on a granular surface.

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Physics, Astronomy & Cosmology / Re: What is Important About Instantaneous Age Changes in the Twin "paradox"?

« on: 05/09/2018 16:06:23 »

My reasoning may be wide of the mark, here, so I would value comments.

Acceleration involves a change in speed, direction or both, thus, the “turn-around” constitutes acceleration.

The “twins paradox” comes about as a result of time dilation and length contraction. 

The Lorentz equations, which gave mathematical veracity to time dilation and length contraction, feature only time, length, velocity and the speed of light.  There is no mention of acceleration.

Einstein incorporated time dilation and length contraction into SR, and SR is concerned only with uniform motion.  There seems to be no need to venture into general relativity.  So why do we have to use acceleration to solve this particular paradox? 

You are forgetting the relativity of simultaneity.  While time dilation and length contraction are only dependent on the speed difference between two frames,  the relativity of simultaneity is dependent on the velocity difference, which involves direction.
For example,  if you are traveling between two clocks A and C while passing a third clock B, and assuming that A, B, and C are synchronized in their own rest frame, then:
If you are traveling from A to C, then clock C will be, according to you, ahead of clock A in respect to what time it reads and if you are traveling from clock C to A then according to you, clock A will be ahead of clock B.

A numerical example:
You're traveling at 0.6c relative to the three clocks, for which the proper distance between the clocks is 1 light hour.
You pass clock B while it reads 12:00, while traveling towards A,  At that moment, according to you, Clock A reads 12:36 and Clock B reads 11:24
On the other hand, if you pass B at the same speed while going from A to C, then Clock A reads 11:24 and Clock C reads 12:36 at that moment.*
If you were to suddenly reverse direction as you pass B, while initially traveling from A to B, then clock A will "jump" from reading 11:24 to 12:36*

Acceleration comes into play with time dilation and length contraction when it involves a change speed, as changing speed changes the magnitude of these two effects.   Acceleration additionally effects the relativity of simultaneity when it involves a change of direction.


*Keep in mind that this is the time it "is" at these clocks and not the time you would "visually see" on these clocks.  In all these examples, when you are next to clock B when it reads 12:00, both you and an observer sitting by clock B would be visually seeing images of Both Clocks A and C reading 11:00.

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Physiology & Medicine / Re: Honey against sugar: which sweetener should I use?

« on: 27/08/2018 09:41:29 »

Could the phlegm be a biofilm and if so, might BC have found the answer?

No, plegm works against biofilms in the trachea. You might find this interesting. http://sitn.hms.harvard.edu/flash/2018/mucus-keeps-us-healthy/

As I said, honey does sooth the throat, maybe it suppresses the biofilm and hence decreases need for phlegm. Did you take it neat? Most people dilute it which reduces any effectiveness. Have you tried ordinary honey? There is no doubt that honey is antibiotic, question is, is Manuka more so?

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Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?

« on: 27/07/2018 00:14:25 »

Another important point, that has been mentioned in this thread, but not explicitly focused on is this: Nothing can ever be known exactly--there is always some uncertainty.

It is absolutely crucial to distinguish between uncertainty - the confidence limits of a measurement - and indeterminacy - the fact that ΔpΔx ≥ h.

We can measure the density or x-ray diffraction pattern of solid hydrogen and thus deduce the effective diameter d_H of a hydrogen atom with an uncertainty of, perhaps, ± 0.1% But the fact that  d_H >> d_proton is due to the indeterminacy of the electron.

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Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?p

« on: 12/07/2018 18:04:12 »

Certainty is undefined. What we know (with absolute certainty!) is that either ΔpΔx ≥ h, or the universe would collapse to a singular point. It hasn't, and we have a pretty good idea of the value of h. 

Thinks for clarifying that.  All I have to do now is work out why the Universe would collapse. 

Easy. If ΔpΔx = 0, every electron will spiral in to the nucleus of its atom, emitting a continuous spectrum of electromagnetic radiation as it does so. That's just classical electrostatics and  electrodynamics, and is the Achilles heel of  the classical Bohr atom.

As h > 0, there are finite solutions to the Schrodinger equation and thus nonzero orbital dimensions and shapes, with quantised energy differences between them. Hence a noninfinitesimal universe, the hydrogen bond, stereochemistry, and us. Though the existence of politicians, philosophers and priests still baffles me. What are they for?

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Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?

« on: 06/07/2018 18:03:08 »

The Copenhagen Interpretation of quantum theory holds that there is no reality at a quantum level, without observation.

And there's the problem. You start with an undefined and probably undefinable concept "reality" then add an equally undefined "observation". That's OK if you want to build a mathematical model in which the undefined variables cancel each other and you end up with a testable prediction, but you can't take the axioms too seriously. It's a bit like "aether" and "conventional current" - helpful but ultimately meaningless!

It's generally preferable to begin with experimental observations, e.g. light is quantised, and work out how these relate to other experimental observations like atomic spectra.

Heisenberg's indeterminacy is mathematically obvious, and no more than a correct formulation of Zeno's paradox. Speed is Δx/Δt, position is x. The larger we make  Δx and Δt, the more precisely we can measure their ratio, but the less meaning we can assign to either x or t. The clever bit is mixing in mass, then guessing that ΔpΔx ≥ h, so whilst we might have a very good idea of the position of a cannonball at any given moment, it becomes very difficult to locate an atom or an electron as m decreases. Ultimately this explains why the hydrogen atom has a finite (but fuzzy) diameter instead of collapsing, and to everyone's surprise h turns out to be a universal constant.

The key to quantum physics is, I think, to accept and use it as a series of statements about what actually happens and not to attempt to derive or "interpret" it from common sense, philosophy, or classical physics.

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Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?

« on: 06/07/2018 08:43:46 »

I agree with @chiralSPO it is our attempt to rationalise the quantum world which gets us into trouble. We try to find mental hooks to hang ideas on so we say that because a wave’s energy can be counted in integer units and because it carries momentum it has particle properties (and we end up forgetting that other waves can carry momentum). We also talk about tunneling, but no one suggests that the particle/wave digs a little hole!
I view Copenhagen as a set of rules for using a methodology that gives amazingly accurate answers, but like most analogies and methodologies these rules can be overextended to give even greater confusion.

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Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?

« on: 06/07/2018 04:28:35 »

Heisenberg, in developing his case for the uncertainty principle, used the example of “observing” an electron by hitting it with a gamma ray photon.  This act established the location of the electron, at the instant of contact, but gave no information about its velocity.

Bohr used this same example in defending complementarity; arguing that it supported the contention that “observation” created reality, in the quantum realm. The reasoning seemed to be that the electron had neither position, nor velocity, until an observation was made.

This must raise the questions: What was the gamma ray photon aimed at?  And, what did it hit, if the electron was not there before it was hit? 

As far as I understand it, the problem with this line of reasoning is that electrons aren't actually particles, and neither are gamma rays (and neither of 'em are waves either!) None of these phenomena have any macroscopic analog that offers an intuitive and accurate way of thinking about them--that's how we get into trouble!

Instead of trying to think about a discrete point particles, consider two intersecting infinite (but not evenly distributed) blobs that are going to interact somewhere within their intersection. "Before" the interaction occurs, the best we can do is offer up a probability distribution of where the most likely times and places of the interaction will be, based on information we have about the histories or environments of these blobs. The "time" and "location" of this interaction do not mean that two point particles collided at that precise time and place. No, it merely means that this is when and where the two blobs interacted--no more, no less.

I know this isn't that much more satisfactory than the "shut up and calculate" philosophy, but I think it is very important to remember that subatomic particles aren't mysterious because they are magical--they are mysterious because we are simple creatures that can only understand things by experience, and we really can't experience anything remotely close to the reality of this scale.

Some of QM does kinda boil down to epistemology: we can imagine tiny particles whizzing around at (nearly?) infinite speed, guided by some waveform that only becomes apparent when multiple observations can be made. And maybe this is "actually" how it is. But I doubt it. Even if a ridiculous model ends up making excellent predictions, and lines up well with observations, that doesn't mean that the ridiculous (untestable) parts are true too--those are just there so we have something to imagine.

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Physics, Astronomy & Cosmology / Re: Is there a difference between zero energy and a zero balance of energy?

« on: 25/06/2018 06:28:42 »

Are you thinking of transformations Bill?

No. I'm thinking: is there a difference between no energy and two lots of energy, each of which cancels  out the other, but both of which remain. 

  The question to ask is what was the energy balance during this process and how does it relate to the current state of the universe?

OK, so I asked the wrong question!  Does this mean that no one knows the answer to my question; there is no answer to my question; or, my question is so silly, it makes no sense to anyone other than me?

No it wasn't the wrong question at all. I just extended it. There can never be just zero energy. Otherwise nothing exists. The energies can balance out. Imagine an object at its apex of a trajectory upwards in a gravitational field. The kinetic and potential energies balance. This does not mean that the energy of the object is gone. It still has rest energy.

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Physics, Astronomy & Cosmology / Re: Can time emerge?

« on: 12/06/2018 19:06:19 »

If you want to take this further then it might be instructive to browse the following article. Where ER=EPR.
https://www.sciencenews.org/blog/context/new-einstein-equation-wormholes-quantum-gravity

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Physics, Astronomy & Cosmology / Re: Can time emerge?

« on: 12/06/2018 12:28:10 »

Wheeler deWitt and the emergence of time.
https://medium.com/the-physics-arxiv-blog/quantum-experiment-shows-how-time-emerges-from-entanglement-d5d3dc850933
An interesting read and not that long.

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Physics, Astronomy & Cosmology / Re: Would your eyeballs really freeze up when exposed to space?

« on: 29/04/2018 19:49:26 »

The fact that the pressure is low and the eyeball is quite strong.

I'm trying to interpret that in a way that gives me information about the possibly explosive fate of the eyeball.  Are you saying that the eyeball is strong enough to withstand internal pressure if exposed to a situation of zero pressure?

When trying to see whether a barrier will collapse "due to pressure," one must consider the pressure on both sides of said barrier. For instance, 20 atmospheres is a lot of pressure, but if both sides are under 20 atmospheres, there is no net pressure pushing the barrier one way or the other.

In the case of an eyeball in space, we can take the pressure of space to be 0 (it is ever so lightly greater than that, but it doesn't matter for this level of calculation), and we can take the pressure from the water to be the vapor pressure of water. At body temp (37 °C) the vapor pressure of pure water is 47.1 mmHg (0.062 atm, so not much), and the vapor pressure of the fluid in your eye will be lightly less (maybe 5% lower?) than that because it is not pure water (and the impurities are mostly proteins and salts, which are not volatile).

So if we assume a pressure of 45 mmHg, which is about 0.6 N/cm², this wouldn't be comfortable, but I don't think it would burst your eye.

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Geology, Palaeontology & Archaeology / Re: Was the 12th dynasty of Egypt ruling at the time of the exodus ?

« on: 29/04/2018 15:58:58 »

The Bible story about the Exodus is constructed of different historical events from different periods, but there is some historical backround. Hyksos played an important role in that event. They had ruled Egypt (Kemi at that time) several centuries earlier and when they had left, people who had supported them and other Apirus or Habirus (falsely labeled as "Israelites"), mainly followers of the Old Kingdom tradition, had been surpressed in Egypt.

The Sea People who were so called Habirus as well, supported Hyksos (related tribally to the Old Kingdom elite) who had settled in Levant, and some rebellious circles in Egypt. Many of The Sea People troops were captured and enslaved to quarries when they had attacked Egypt. All these people were Habirus, whose Sumerian based name has been wrongly transformed as "Hebrew". They were not ancestors of modern Hebrews, but Sumerian- Aryan people (Y- haplogroup R1a), descendants of the priestly and kingly elite of Sumeria and Ancient Egypt. Hyksos (originally Haka-Kasvut) were their tribal brothers.

After Seti II died, his wife Meryamaan Twasarat (Biblical Mirjam) took power with her lover vizier Bay (Aria/ Kuru), who became know as Aaron.  There was a destruction in Egypt during their rule. Rebellious people destroyed temples and looted everywhere, demanding a religious and cultural change in Egypt. Pharaoh Amenmose (originally Sama Moni/Muna), who had co-ruled with Seti II, was part of the team and he became known as "Moses" in future.

This team asked Levantian Hyksos to help them. It is estimated that about 150 000- 200 000 Hyksos came to help with the rebellious who had now liberated also the enslaved Sea People Habirus from quarries. However, they lost at the end and had to leave Egypt with ex- prisoners, leprous, Habirus, Hyksos etc. Part of them directed to Levant, and part of them invaded Greece and finally established a Hellenic high culture there.

I would like to underline, that "Moses" or Amenmose (Sama-Moni/Muna) was tightly related to Hyksos and he even used a Hykso title "Haka-Wasat", which is falsely translated as "Heka- Waset" by ignorant egyptologists.

Hyksos or originally Haka-Kasvut weren´t Asiatic or Semitic, but Aryan Habiru people who had left Egypt during and at the end of the Old Kingdom to establish mines and metal cultures. Arkaim was one of these sites established by Kemi-Egyptian Aryans and they became known as "Hyksos". The problem is that egyptologists have no idea about the language used by Aryans. Their names are systematically wrongly translated.

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Physics, Astronomy & Cosmology / Re: What is a tensor?

« on: 18/04/2018 18:09:24 »

@geordief @Bill S
Just been searching net, try this, easily digested

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Physics, Astronomy & Cosmology / Re: What is a tensor?

« on: 17/04/2018 15:37:42 »

@PmbPhy and @jeffreyH understand tensors and will give you very sound answers with no waffle, but as @Bill S says, perhaps you need to step back a bit.

So ,if in any medium (or apparently also even in a vacuum) any point is associated with more than one force , these forces can be represented by vectors and they are called tensors when they all originate and combine at this one point....

Let’s start by forgetting medium, vacuum, forces, and combining at one point.
Vector is a simple tensor rank 1. Examples can be a force+direction or speed+direction.
Tensors aren’t limited to these values because a tensor is just an array of numerical values that can be used to describe the state or properties of a material or point in space.
Let’s take a simple example of stress. Stress, like pressure is defined as force per unit area and a material can support different forces applied in different directions. Imagine a cube of material with forces acting on it in three dimensions, the stresses on the cube can be obtained and stress state can be represented by 9 components - 3 for each face, force component and 2 components for the area of the face. Hence a second rank tensor.
Stress, strain, thermal conductivity, magnetic susceptibility and electrical permittivity are all second rank tensors, piezoelectricity is described by a third rank tensor, elasticity of single crystals is described by fourth rank tensor.
So very useful, particularly when you add the transformations and operations that @PmbPhy  and @jeffreyH mention.

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Physics, Astronomy & Cosmology / Re: What have I missed regarding This Einstein thought experiment?

« on: 19/03/2018 23:24:12 »

Which bit is incorrect?  All of it?

The bit about how he thought about it is. As Pete says, and I’ll quote Einstien “I should observe such a beam of light as an electromagnetic field at rest.” In other words, the wave would seem stationary, but this was not possible according to Maxwell’s equations, which describe the motion and oscillation of electromagnetic fields.
So he either believed Maxwell was correct or the wave was stationary. He chose Maxwell for the same reason we do, the maths is correct and consistent with experiments of Faraday, Gauss etc.

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Physics, Astronomy & Cosmology / Re: Can we thank Stephen Hawking enough?

« on: 14/03/2018 17:29:14 »

To be honest with you it's the man I'm thinking of and his family.

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Physics, Astronomy & Cosmology / Re: How would we calculate the time left to contact with an EH?

« on: 14/03/2018 10:11:30 »

Are you saying that assertions such as: "To an outside observer any object approaching the Schwarzschild radius appears to take an infinite time to penetrate the event horizon", are incorrect, because the object would vanish before, in the observer's RF, it reached the EH?

Yes.

I hope I don't murder the maths too much, but:
- Let's take Kryptid's calculation of the escape velocity of a black hole at a certain radius: v_e = √((2GM)/r)
- If we are looking at a space probe falling "from infinity", it's velocity at radius r from the center of the black hole will equal the escape velocity given by this equation.
- Plug in the measured mass of the Cygnus X-1 black hole of 14.8 solar masses
- The event horizon is at a radius of r_s=43.6km

For an observer seeing the space probe fall away from him towards the black hole, there would be considerable relativistic doppler redshift, even without gravitational time dilation.
https://en.wikipedia.org/wiki/Relativistic_Doppler_effect#Motion_along_the_line_of_sight

But let's ignore Doppler shift, and put the observer at right angles to the infalling probe, so there is very little Doppler shift.
So now the main source of frequency change is due to gravitational time dilation. This frequency ratio is sqrt(1-r_s/r)

If the distant observer looks at the speed of the infalling space probe, and does a linear extrapolation of the time to impact with the event horizon:
D: Distance to event horizon, in meters
v/c: Velocity, as a fraction of the speed of light
T: Extrapolated time to impact event horizon (in seconds)
TD: Gravitational Time Dilation ratio = ratio of emitted frequency of light to frequency as seen by the distant observer


D(m)     v/c    T(s)   TD
10000   0.902   4E-05   0.432
 1000   0.989   3E-06   0.150
  100   0.999   3E-07   0.048
   10   1.000-   3E-08   0.015
    1   1.000-   3E-09   0.005


If the infalling space probe had a bright beacon on it,
- at 10km its frequency would be halved, and you would predict impact in about 40μs.
- at 100m, it's frequency would be reduced by a factor of 20, and you would expect impact in 0.3μs.
- at 1m, it's frequency would be reduced by a factor of 200, the received power would be reduced by a factor of 200, and you would expect impact in 3ns

You could extend the visibility for a nanosecond or two by using an X-ray beacon, or even setting off a gamma-ray burst with an atomic bomb.

I am sure there is some factor I have missed, but I think the general conclusion is valid - a remote observer would see the space probe approaching the event horizon at a relativistic speed, and around the expected time of impact, the frequency of the beacon would be reduced to undetectability within a very short time (effectively zero frequency and zero emitted power), so it would look as if the space probe had crashed into the black hole and disappeared
See: https://en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphere

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Physics, Astronomy & Cosmology / Re: Is there anything more south than the south pole?

« on: 06/03/2018 07:30:12 »

Valid as this might be mathematically, it involves imaginary time.   Is there a fundamental concept of imaginary time in physics?

As you know imaginary numbers were very much misnamed when discovered, but they do have a physical significance in many situations. In the case of imaginary time there is no physical significance needed, as used by Hawkins, it is a mathematical work around by changing the metric to a Euclidian space which is far easier to handle. If you want to imagine what has been done, it is like rotating the time axis 90 so it is still orthogonal to the 3 space dimensions but now has the same sign (using East Coast convention). It’s known as a Wick rotation if you want to look up details.

I fail to see how drawing an analogy between the two-dimensional surface of the Earth and three-dimensional spacetime solves the problem of something emerging from nothing.

Hawkins was interested in a slightly different issue which is whether the start of time for our universe is from a point eg like a singularity or from a smoother surface - a boundary. A Euclidian space can be modelled as if it is surface of the earth (but you have to imagine that surface is 3 space dimensions) and if you imagine the start of time as the S Pole (in some lectures he uses N Pole) with time axis pointing to N Pole and 2 of the 3 space dimensions at rt angles , then the expansion from the s pole moves up the surface of the earth as a series of time-slice circles (but in 3D). The point about starting from the s Pole is that it is a smooth curve (boundary) rather than a sharp discontinuity like the point of a cone.
Hope that makes some sense.