out on a limb without a wave to hop on

Phil
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Merle, This may not be

Merle,

This may not be exactly what you are looking for, but I have a suggestion.

While the latest version I am aware of was published in the late 90s, Stephan Hawking's "A Brief History of Time" was a good read for me.

It covers a lot of territory from Black Holes to Quarks and such. Stephan has a way of explaining things so us non-scientists can understand imho.

I urge this thread to continue. Fascinating stuff!

Phil

merle van osdol
merle van osdol
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Thanks Phil, I heard that

Thanks Phil,
I heard that said about Einsteins - for laymen and about Asimo's Understanding Physics but I'm a real Dummy. I'll try Hawkings book, maybe that will do it. But you know I get substantial insight from Mike on this forum on these subjects and of course the best part is that I can ask specific questions. Over time I can absorb this stuff, I believe.

merle

What is freedom of expression? Without the freedom to offend, it ceases to exist.

— Salman Rushdie

Phil
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Hi Merle, I would never

Hi Merle,

I would never suggest a book taking the place of Mike. Heck, I learn tons from him, too! Mostly about how nutty Aussies are, hehe.

Seriously though, I suggested the book as an additional resource I personally enjoyed. There is never a substitute for being able to ask specific questions.

Phil

Mike Hewson
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You Rang ??? :-)

You Rang ??? :-) :-)

Quote:
Would the quantum people then believe that we won't find a gravitation wave?


Not at all. The issue is not belief here, it is the provision of an explanation of gravity ( any aspect ) from a quantum point of view.

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Also, If they say that fermions can't be stacked, how can they explain neutron stars?


No two Fermions can occupy the same state, you can have as many Bosons in the same state as you like. In the simplest sense consider that state = same place at same time with same energy/angular-momentum/spin. So Fermions are like cars on a freeway, you can't have them occupying the same slot in the traffic. The equivalent for Bosons is two cars literally superposed in/on/within each other on the freeway. If you like Fermions are nature's way of preventing everything being in the one place. It is why I don't fall to the floor when I sit upon a chair.

Now neutron stars are 'stacked' - layered if you like - as the neutrons are fermions and they can't all be at the middle. The density of neutron star material is quite enormous, neutrons just jammed together. Whereas everyday atoms are mostly empty space - a nucleus and way away are some electrons circling at distance - there is no free room in the neutron star. Some express this by saying the star is a gigantic nucleus. I think some sci-fi writers call this 'neutronium', but as I don't personally know any such authors that's just a guess.

Estimates put the outer crust of a neutron star having the density of iron nuclei, with a billion-fold increase towards the core. But the key problem is that we have no ready sample to test, they are all some light years away and we can't reproduce the relevant conditions here on Earth. Only several Sun's worth of mass compacted into a few tens on kilometers can achieve that. So these numbers are projections based on what we do know is true around here. This is the moot point : what actually happens to matter at such a crushing density ?

FWIW : too much mass inside a given volume yields a black hole. Now the GR equations specify that, and an event horizon is formed. At that horizon radius then light - following shortest spacetime paths - will find that is a wrapped/recurrent surface. But what is at the centre of the hole ? Once sufficient mass lies within the required radius then from then on the exterior universe will only 'see' that horizon. Pure GR doesn't stop everything going inwards to a central singularity. Infinite density. But will QM come into play, Pauli exclusion forcing some minimum distance b/w matter particles ?

Quote:
Why don't the neutrons in neutron stars decay into protons like you said in one of your prior comments (in about a half an hour)?


Because they are not alone. It is the sole neutrons ( away from close company of other neutrons/protons ) that readily decay.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
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Addendum : There is a higher

Addendum : There is a higher level 'point of order' applying here. It goes way back to the original structuring of the theory that is quantum mechanics. One may safely sleep at night, sanity unchallenged, if you ignore what follows. Caveat Draco ....

First there was the 'old quantum mechanics', say prior to about 1924 ( roughly ). This took classical physics with the point particle concept and classical forces specifying detailed trajectories of them. There was the idea of a path through space which these particles took, even when we weren't looking. Ad hoc restrictions were placed on these paths, say by requiring that an electron orbit in an atom must have fixed amounts of angular momentum, and with the right choice of numbers one could obtain a fit with some particular experimental data set. But there was no methodology to take some new scenario and predict in advance what the measurable outcomes would be. It was always fitting after the fact, and no ready transference of interpretation from one experimental situation to another.

Enter Mr Heisenberg. His first thrust was to state that what matters is not what we think the particles are doing ( when we do or don't see them ) but only what we can measure. So he began at square one taking the measurable quantities as the 'truth' in any situation. In particular electron orbits were a superfluous concept if one could never measure them. For to do that one would have to interact in some way, marking the position of the electron at certain times and then reconstruct a path by joining the dots. Think of a drive across the countryside and only being monitored at a few places : you went through Chicago at such and such a time, then Salt Lake City at some time, followed by Dallas a day later ..... not knowing American geography at all well, this could be a ridiculous trip however. In any event how can one say where the car was at times when not noted? But it is much worse than that. Imagine a measurement of a single data point of your trip - passing through Las Vegas say - that literally destroyed the trip. One look at where the car is and bingo - you will have no idea at all where it will be from then on, it may not even be in the USA. It could have been shot into space. So

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the act of measurement irrevocably disturbs the system of interest. After the measurement it will do something ( radically ) different to what it would have done if not interfered with.


So why does measurement fracture these small systems under study ? It is because the 'probe' that you use to measure with has a certain minimum influence. All particles can be probes, in theory at least, but they all have one crucial characteristic

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the more precise the probe is, then the more energetic it is and the greater influence it will have on the evolution of the system after the measurement event.


Hence any measurable quantity has it's price, whether that be position, momentum, energy, angular momentum, spin or whatever. The more exact the answer you want for said quantity then the more you change what you were watching. The exact relationship between what you measure vs. what you have disturbed is encapsulated in Heisenberg's Uncertainty Principle ( HUP ). This does not mean everything is uncertain. Far from it. HUP applies to certain pairs of observable quantities, which in this context are called conjugate. The usual one quoted is momentum with position. You can measure either alone to any desired degree of accuracy, but for simultaneous probes ( ie. same time and place ) that cannot be met. The more you get to discover about one the less you can determine about the other. So if I determine an electron's momentum to the limit of today's technology say, then subsequently I could not say it even resides in the laboratory at all! Where'd who go ..... ???

Perhaps one could be clever and try the conservative Three Bears Approach, not too much precison/disturbance. Fair idea. Unfortunately things now get a wee bit weirder. Suppose I tried to 'moderately' measure position and then 'moderately' measure momentum. This seems a reasonable approach as for most practical purposes you don't want your results to some high Nth degree anyway. What happens is

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for a sequence of measurements on conjugate variables ( those that relate via HUP ) the final system state depends on the order of the measurements


So if I compare the state after position was measured followed by momentum, with the state where momentum was measured and then position, these final states must always be different. The quantifier for this difference in outcomes ( when comparing measurement order ) is called the commutator. The commutator is in reality a two-part thing : a magnitude and a phase, together called a complex number. Crucially it is not zero. The commutator is not reducible, not trade-able for something else. It just is. Fact Of The Universe type of thing. The absolute value of the commutator is Planck's Constant which in everyday terms is vanishingly small, around 10^[-30] in the relevant MKS units. The phase part is just as important and is often disclosed in 'multi-path' constructs.

Now why did we not know this from the get go ? Why did only the 20th century discover this ? Why didn't Newton mention this in his Principia ? Because

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in practice none of this measurement guff matters unless the system ( or the components thereof being studied ) are of such a scale as to make Planck's constant comparable.


Historically we studied the big things before we got to the small and hence you can't get out of traffic citations by fronting up to the judge with a QM line of reasoning. One can slide from classical to quantum physics, and vice versa, by scaling your system to study with respect to the absolute value of Planck's constant.

There you have it. This is the Mad Hatter's Tea Party* of physics. No one at present has any better program for understanding the very small. However following the QM program is incredibly successful and we must therefore accept - as true scientists - the lessons of experiment.

Moot Punchline : so the interior of a black hole, by definition, remains unmeasured by anyone/anything outside the horizon. While one may sweep this under the rug in a classical discussion, you simply cannot accept that if you wish to apply QM. That is one reason ( at least ) why QM and GR, as currently proposed, don't mix.

The Tenth Yard : I'll assume you're not completely hypoxic from the above discussion.

(A) If you take a black hole, fully formed with all transients resolved then from the outside one can only measure the following intrinsic properties ( not specially dependent on choice of distant viewpoint ) : mass, angular momentum and charge.

(B) What are the measurables for a fundamental particle ? That's ..... err ..... mass, angular momentum and charge ! For sure the particles we find at a subatomic level also have other quantum numbers associated with them, but they depend upon circumstance and group interactions.

This could merely be an accident of how we go about thinking, a co-incidence of ideas or analogies in human heads, rather than a real connection that would be a requirement of this Universe.

However some wags have proposed the contrary. This being that the little particles are in some sense wee small closed off volumes of spacetime. Just like black holes. This is a legitimate conclusion, at least for the purpose of modelling. Unfortunately this concept led unnecessarily to the legal challenging of the LHC operation. The base problem there was not that fundamental particles, of whatever energy, would create black holes and swallow us all up. Not at all, as if so cosmic rays ( whose per-particle energies beggar belief and go way beyond anything we can artificially cook up ) would have done that ages ago and we wouldn't be here to converse on the topic. It did definitely prove that otherwise clever people always run the risk of being too clever ( I include myself here ) and Bozo** it because of lack of domain knowledge and willful ignorance to properly inquire, propelled/charged with ego.

[ .... if you need a lie down after reading this, ditto ! I need a lie down after writing it .... :-) ]

Cheers, Mike.

* ie. any movie you see starring Johnny Depp with Helena Bonham Carter must have been directed by Tim Burton. [ gratuitous Dad Joke ]

** Bozo used to be the iconic circus clown. More recently you can chose and replicate the logic.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

merle van osdol
merle van osdol
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So at last I started reading

So at last I started reading my Asimov book on Understanding Physics. One thing it said is that everything can be viewed as particles or waves depending on the particular viewpoint.

Can we calculate the mass/earth weight of 10 million photons? Exactly, approximately or not at all?

I'll always try now to check Asimov before I ask a question here. Is Hawkings book on 'Time' because it had been more recently published any more helpful to a beginner like myself?

Danke sehr,

merle

What is freedom of expression? Without the freedom to offend, it ceases to exist.

— Salman Rushdie

Odysseus
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RE: Can we calculate the

Quote:
Can we calculate the mass/earth weight of 10 million photons? Exactly, approximately or not at all?


A photon has zero rest mass, and the amount of energy it carries depends on its frequency, according to the Planck-Einstein equation E = hν, where h is Planck’s constant. Combining that with E = mc² we can write m = hν/c² for the mass equivalent of a photon’s energy (assuming it’s in vacuo, therefore travelling at c). Supposing the ten million photons are in the middle of the visual spectrum, green light with a frequency of 550 THz, I make their total mass equivalent about 4.0 E-26 g (.04 yoctograms). Radio photons will be far less energetic, and conversely gamma rays much more so.

merle van osdol
merle van osdol
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RE: RE: Can we calculate

Quote:
Quote:
Can we calculate the mass/earth weight of 10 million photons? Exactly, approximately or not at all?

A photon has zero rest mass, and the amount of energy it carries depends on its frequency, according to the Planck-Einstein equation E = hν, where h is Planck’s constant. Combining that with E = mc² we can write m = hν/c² for the mass equivalent of a photon’s energy (assuming it’s in vacuo, therefore travelling at c). Supposing the ten million photons are in the middle of the visual spectrum, green light with a frequency of 550 THz, I make their total mass equivalent about 4.0 E-26 g (.04 yoctograms). Radio photons will be far less energetic, and conversely gamma rays much more so.


Thanks oh Traveller,
So it does have mass when traveling. When it hits something the energy it had is
absorbed by some matter. Then there is no such thing as a photon at rest. Sound OK?

merle

What is freedom of expression? Without the freedom to offend, it ceases to exist.

— Salman Rushdie

merle van osdol
merle van osdol
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In '66 Asimov spoke of

In '66 Asimov spoke of graviton's. Do physicists still speak of graviton's? Can you calculate the weight of graviton's like you can of photons? The gravitation wave that we try and measure will expand or contract some object (laser beam or whatever) and we will say we directly measured the GW, if I understand it correctly. Is it theoretically possible to ever "see" a graviton in other words bring it to a focal point like we do with the photon or is that what LIGO indeed is trying to do?

Thanks to all for your patience with me.

merle

What is freedom of expression? Without the freedom to offend, it ceases to exist.

— Salman Rushdie

Mike Hewson
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RE: In '66 Asimov spoke of

Quote:
In '66 Asimov spoke of graviton's. Do physicists still speak of graviton's?


Not in polite company ! :-))) Seriously it is a big unanswered question ie. as to whether we can legitimately talk of 'little bits' of gravity. That's what quantum means here, a little quantity. Quanta is plural. The graviton would be the quantum of gravity.

Quote:
Can you calculate the weight of graviton's like you can of photons?


Well you can assign an energy equivalent to a gravitational field. But the thing to note is that, at present, the field is very much an extended entity ( not compressed and localised like photons ). So the energy is distributed across some region of discussion. Here you may note this is a self referential comment, as that field energy by definition must also gravitate in the same manner that the field generating masses did ! Because mass and energy are different labels for the same thing. It is just that traditionally we have used what were previously thought to be entirely different measurement units/scales. One was measured in grams/kilograms/pounds/brontosaurus-legs whereas the other was measured in watts/ergs/electron-volts/yada-yadas.

[ This is probably one of the hardest things to swallow with The Relativities : 'mass' and 'energy' is a historical dichotomy of thinking. Or if you like mass and energy is a low energy approximation/partition of reality. The E = m*c^2 scale conversion equation is an inevitable outcome of requiring general conservation laws to apply in different frames, while also transforming b/w said frames using the Lorentz formulae. ]

Quote:
The gravitation wave that we try and measure will expand or contract some object (laser beam or whatever) and we will say we directly measured the GW, if I understand it correctly.


There are two sides to the one coin here. One can say :

(A) the objects distort as the GW passes while your measurement system stays constant, OR

(B) one can say the object is truly rigid but your metric varies.

The cognitive difference is whether you think 'spacetime' exists independently of us, or whether we just use the concept of spacetime as a summary of our measurement efforts. This is admittedly a bit woolly ( or my understanding is !! ) but fortunately the predictions are the same either way. Some of this goes way back to ideas of Ernst Mach's thoughts on inertia and Isaac Newton's analysis of a rotating bucket of water! For LIGO the phase differential between the two arms is the same regardless of viewpoint [ A and B are choices of descriptive frame on a spectrum of alternatives ].

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Is it theoretically possible to ever "see" a graviton in other words bring it to a focal point like we do with the photon or is that what LIGO indeed is trying to do?


No, and no.

Quote:
So it does have mass when traveling.


It has mass/energy. See above.

Quote:
When it hits something the energy it had is absorbed by some matter.


.... and momentum too. This is the basis for 'light sails' that you may hear of ie. scooting around the solar system using the push of light to propel some craft. Indeed the alleged anomaly with the path of a Voyager craft was due to differential heat radiation from a barely functioning onboard generator, so in this case an effect from the push of infrared photons.

[ .... that Voyager effect has been known and squared away for some years. Alas it is still being quoted by Area51/X-files/Face-on-Mars thinkers as a mystery of the universe*, NASA conspiracy etc ... ]

Quote:
Then there is no such thing as a photon at rest. Sound OK?


Bingo. Always moving, never stationary. More so : it always goes the same speed ( for inertial observers ).

Cheers, Mike.

* ... or for that matter an author that puts the rhetorical question in the book's title knowing full well the resolution is a matter of meticulous engineering and modelling .... not a Carl Sagan level of concern at all.

( edit ) Also I really am getting sick of popularist books that gratuitously name drop famous scientists well out context, while trashing any hopes of readers understanding the topic :

What Was Albert Einstein's Cook's Left Elbow Thinking ?

Schroedinger's Cat's Litter Tray : The Poop Conundrum That Has Theorists Baffled.

Heisenberg Wasn't Sure If He Would Take The 10.15 Bus Or The 10.05 Train.

News Flash : Newton Failed To Predict Satellite Experiment Done Four Centuries After He Died ....

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

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