1

Physics, Astronomy & Cosmology / Re: Is light an independent entity, or is it an effect of a larger mechanism ?

« on: 14/10/2019 10:11:54 »

Concerning a particular type of particle which, when its 'state' was changed then a matching particle's state also changed - instantaneously, no matter how widely seperated in distance (thus appearing to break the lightspeed limit).

You are hearing about entangled particles. Difficult to describe in detail, but it has to do with correlation and quantum statistics and also what we know about the particles.
An analogy: lets say a friend puts a rh glove in one envelope and a lh glove in another but doesn’t tell you which is which. We could say the contents of those envelopes are entangled and there is a correlation between the ‘state’ of the gloves in each envelope.
So, you now send one envelope to another person on other side of the world and keep one. If you open your envelope (measure the state of your glove), you instantly know the state of the other glove, but nothing has changed other than your knowledge. We can do the same with particles eg electrons or photons and when we measure the state of one we can be sure of the state of the other.
However, quantum statistics are more complicated than everyday statistics so this is a fascinating area of misunderstanding, and you will need some maths to understand what is happening.

2

The Environment / Re: What's the difference between a typhoon and a hurricane?

« on: 12/10/2019 23:12:53 »

Surely the answer is that we've had a hurricane - but not a typhoon - in snooker...?

If his surname had been Timmings you could have had Typhoon Timmings.

3

Physics, Astronomy & Cosmology / Re: What is the cosmic microwave background?

« on: 12/10/2019 09:18:31 »

The conversation seems to imply the CMB generation was quite a short phase (when the universe was a 3000k plasma). If its effects are still saturating the universe after 13.7bn years (due to its photons filling cubic meters of space as fast as they leave it), then the volume of this plasma must have been.... 'large'. But, why dont we see other radiation that must have been emitted before and after this 3000k period?

To add to what @Halc said, I’m giving a very simplified analogy.
Think about a light bulb, lots of very bright light. Switch it off and you will see the light fade quickly and the filament still glow red for a while. Now touch the glass, still very hot, move the bulb 100m away and a thermal imaging camera will still pick up that heat (infrared) radiation.
Now imagine a universe filled with light bulbs (lets ignore for the moment the inflation that put them there) if they are all switched off together they begin to cool, but still radiating. When the ones next to us have cooled, all of them will have cooled, but the radiation reaching us from the ones billions of light years away was emitted when they were still quite hot - less hot than IR and was down to microwave frequencies.

4

The Environment / Re: Why are the suns rays hot some days and not others?

« on: 10/10/2019 09:08:09 »

Thank you colin, in the days of continued sun during even elevation, such as june july august, the rays also become stronger the longer the continued sun happens. I am wondering whether this is the greenhouse effect of higher water vapour content increacing the radiation felt.

There are a lot of different factors at work here.
Firstly, the elevation of the sun will increase during the day, hence less atmosphere to pass through at midday compared to early morning.
Also, the temperature of the air around us will have an effect on how we feel the effect of direct sunlight, certainly water vapour in the air will affect air temperature close to the surface due to reradiated surface heat.
Interesting question - if the air around you is cold do you feel the sun’s rays as warmer than if the air is warm?

5

The Environment / Re: Why are the suns rays hot some days and not others?

« on: 20/09/2019 10:12:22 »

If you consider the elevation of the sun, rays have a lot more atmosphere to pass through in winter, hence greater absorption of IR.
Also, if you consider the energy/m² in a plane perpendicular to the rays then consider the angle of ground relative to the rays you will see that the energy is spread out over a greater area in winter reducing the heating, and hence air temperature, next to the ground.
Obviously, if you are standing then you are closer to the ray perpendicular, in which case the distance through atmosphere has greater effect.

6

New Theories / Re: Are all photons mediated in the same way through the quantum vacuum

« on: 09/09/2019 18:12:34 »

Catching up after being away, so short reply:

"In QFT, a photon is transmitted through the vacuum by ripping electron positron pairs from the vacuum." came from memory ....should have read "the bare photon propagates while tearing electron positron pairs from the vacuum" .

I think you’ll agree that these 2 sentences convey very different meanings so it’s important not to misquote. Mention of bare photon sounds as though you are going through renormalisation at this stage. I also assume you understand bare particles, if not it’s important to go through the derivation because it gives some insights into the models being used and why adjustments are necessary.

It was an illustration offered by the authors to illustrate how a photon is propagated in QED via a creator and annihilator virtual particle pair. One of the authors is from Durham university and the other from Oxford university

This sounds like Stephen Blundell’s book. Because this is aimed at the amateur they quite rightly stick to the formal (shorthand) Feynman descriptions of the calculations, but it does a good job of showing the calculations that lie behind the jargon. Feynman used a very restricted pallet of operations and creation and annihilation are at some of the vertices of the diagrams. The photon is not propagated in QED by creation annihilation operators, they only describe its creation at point eg at A(x,t) and annihilation at say B(x,t) - unlike QM, in QFT/QED the probability of finding an electron or a photon integrated over space does not have to be one, it can change with time. Remember, QED (charged particle interactions) is a simplified subset of QFT - in QFT the photon propagation is described by quantisation of the em field as per Maxwell’s equations.

Why do we, and the science advisors on main Physics fora, plus  top physicists like John Baez, Matt Strassler, etc, say that virtual particles are shorthand for the calculations rather than objects - the legendary Sidney Coleman described them as fairy tales. Well for one it’s what Freeman Dyson said and he was the person who developed Feynman diagrams into the form we see today. When we were undergraduates Feynman’s papers were required reading and in there Feynman says that the particles, eg electrons, interact directly via their fields (no virtual mediation). So what we are looking at are the complex and dynamic interactions of those fields as described by the Feynman diagrams and the underlying calculations. Also, as you will also know from your book, an internal line doesn’t represent a single interaction or even a specific time ordering, unlike the external lines. Interpretation of the internal lines is a temptation but fraught with pitfalls, this is why Feynman said “shut up and calculate. Quite rightly the book you have is teaching you what every student of QED needs to know; how to calculate.

As discussed with Alan the words electron and positron might not be exactly correct, perhaps virtual particle pairs or electron hole pairs would have been a better analogy.

There are a lot of models used in physics and some historical ones are still used in teaching because they can help understanding (eg Bohr atom, although no one now thinks of atoms as small solar systems).
Dirac’s model which used electron holes underwent a number of changes, but never really hit the mark. It was left to Feynman who, under John Wheeler, began to look at the electron under time symmetry (as you know, many models in physics are time symmetric). He found that if you modelled an electron going backwards in time you end up with a positron going forward in time - this is why you will note in the diagrams an antiparticle goes in the opposite direction to its particle, moving backwards against the time axis.

Vacuum polarization via virtual particles is confirmed via the Lamb shift measured in Hydrogen atoms.

Yes, you can model the Lamb Shift  via the Feynman diagrams (http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/lamb.html) and it does confirm the accuracy of those calculations using QED, but does not confirm the existence of virtual particles.
Vacuum polarization describes changes in the distribution of charges and currents of an em field by those generating the original electromagnetic field, it is also sometimes referred to as the self-energy. Again you can model this shielding using the Feynman diagrams and virtual particles, but the Lamb shift only confirms the accuracy of the calculations not the existence of virtual particles as objects.
Again it’s worth understanding the bare electron and why we have to postulate shielding  and renormalisation in the models to reduce the infinities of mass and charge.
Remember, the Shrodinger/Dirac model did not predict Lamb shift, it predicted that the energy levels were only determined by the primary quantum number. This is a problem with the model which considered the electron to be a free electron with point charge, when this is used to model interactions between fields, eg between electron and proton, you end up with infinities for charge and mass. The big contribution of Lamb and particularly Hans Bethe was being able to derive the Lamb shift using the idea of renormalization, which allowed him to calculate the observed energy shift as the difference between the shift of a bound electron and the shift of a free electron. If you look at the 2S & 2P orbitals you can see a difference of how closely the electron approaches the proton and hence the difference in the field interaction/modification.

Vacuum polarisation looks like a radio wave to me, but I might be wrong.

Very wrong. Radio waves are em radiation same as IR, visible light, UV, x rays and gamma rays.
I know you have a personal theory that radio waves are not part of the em spectrum and cannot be described by a photon model, but this goes against all of current QFT. In fact the Lamb Shift experiment is a good example of the existence of radio frequency photons.

My understanding is that space is not an empty vacuum it is full of quantum fluctuations. Also my QFT book used the term in the intro quantum vacuum of space. https://en.wikipedia.org/wiki/Vacuum_state . My terminology might be incorrect, but I think ive got the right end of the stick.

I’m not saying you’ve got totally the wrong end of the stick, although it’s worth noting what the science advisors on one physicsforum say about the Wiki quantum vacuum articles  “written by someone who has only read popsci articles and doesn’t understand real physics”.
What I am saying is the the quantum vacuum is not the energy of space, but of a quantum vacuum in space eg for QED this is the lowest state of the quantised electromagnetic field. It may seem a subtle difference, but it is similar to saying “the stage speaks the authors words” when in fact the stage (space) is where the actors (fields, vacuums, particles, etc) exist. It is also important to recognise that quantum vacuums can exist for any quantum system so it’s important to be specific, see:
https://en.wikipedia.org/wiki/Quantum_vacuum_(disambiguation)

7

Just Chat! / Re: Spam Is One Stop Shop For All Your Auto Care Needs.

« on: 05/08/2019 13:02:29 »

What the hell is a spammer doing advertising melbourne based car services on a worldwide science forum ? Surely there are better target audiences ? Plagiarism services, visa services, etc are understandable, but its a bit like advertising fishing trips of venesuela.

Is this a new kind of bot ?

I’ve been away for a while and nothing changes on the spam front.
We get a lot of these for all sorts of businesses, but manage to remove them before they post. I think they hope to increase their hit rate on search engines by posting links here. Doesn’t help, we replace their website url, usually with ours.

8

New Theories / Re: Are all photons mediated in the same way through the quantum vacuum

« on: 18/07/2019 08:51:32 »

I sorry, but we don’t have the time to run a detailed course on QED/QFT but I’ll try to answer as much as time allows and then suggest that you spend time trying to understand the theory via a course in Quantum Systems.

Feynmans virtual photons are just mathematical simplifications of field interactions, for peasants, which I think I realized already.

you obviously have a very poor opinion of students of quantum theory 
Feynman originally developed the diagrams as a calculation aid for students on his course on quantum theory. Just as Einstein had a ‘thing’ about quantum theory, Feynman had a ‘thing’ about field theory and wanted to express the interactions as particles - there are indications that he later regretted this terminology. The virtual particles are internal processes and are only metaphors for multivariate integrals. The term is often used between researchers as jargon/shorthand rather than meaning particles as we think of them eg electron. The real problem is that in physics a lot of prior understanding is taken for granted, so a QED/QFT text book doesn’t expect you to leap in without studying a few years of physics and quantum theory and so doesn’t bother to explain the background.

I am correct in concluding that Feynmans virtual particles do not exist in reality,

Correct.
The virtual particles are metaphors for multivariate integrals, there are no 'time processes of virtual particles. Nobody ever has written down an equation for the time evolution of virtual particles. While a case can be made that virtual particles exist at least as lines on paper, no such case can be made for their time evolution.

and are not the same virtual particles as those predicted to exist in space by Casimir via calculations based on the uncertainty principle, supported experimentally. Giving rise to various quantum foam/gravity theories.

They are the very same, but their ‘existence’ is not predicted or supported experimentally. Experiments can confirm that results of the calculations represented by the shorthand/diagrams are correct (real).

Further more virtual particle pairs borrowing there energy from the quantum vacuum of space momentarily, are nothing to do with QFT, other than they both use the term virtual particles.

They are the same.

You keep mentioning space when referring to vacuum.
3D space (which can have a vacuum) is not the same as quantum vacuum. A quantum vacuum is the lowest energy state of a quantum system, any quantum system eg molecular bonds, it is not the same as spacial vacuum. If we take a simple Newtonian system eg a weight hanging from a string it has zero energy as it hangs there (disregarding the energy in the mass of the weight and the potential energy which would be released if you cut the string); if you set this system oscillating it will have its maximum ke at the bottom and its minimum at the top of the arc - where it spends most of its time.
The quantum version of this oscillator has its minimum energy at the bottom - where it spends most of its time - but this energy is not zero. This none zero minimum energy is a feature of all quantum systems and is due to the fact that there is uncertainty in the position and momentum of the particles. It’s not that they are flitting about, it’s a way of handling the uncertainty of a probabilistic system.
You don’t really borrow energy from the quantum vacuum, the correct way to look at this is with time/energy uncertainty ie Δt ≥ h/2ΔE . What this is telling you is that if you want to detect the presence or absence of a particle whose rest mass energy (E = mc²) is equal to ΔE, you need to look for at least a time Δt. You can look for longer if you like, but this is the minimum observation time needed to ensure that the uncertainty in your measurement is less than the energy of the particle. If you look for less time, your energy uncertainty will be bigger than the mass energy, and you can't be sure whether the particle was really there or not and in QM the probability is nonzero, but if you look for a longer time they aren’t there - you didn’t see them. Again this is a way of handling uncertainty in the equations.

Adding further to my confusion I googled for a link on evidence for the Casimir effect experiment which I know exists, and stumbled across this link https://www.scientificamerican.com/article/are-virtual-particles-rea/ Which leads me to think perhaps the terminology used by different Quantum theories leads to further confusion

.
He was criticised by a number of physicists for this article as being misleading. Remember also the difference between physics and the maths we use to describe it - "existence" for physics means "measurable", for mathematics "possible to be included in a self consistent theory”, quite often there is confusion in the use of these terms.
I’ve already given you links on the problems of virtual particles being considered real (in the physics sense) and the problem of considering them as cause of Hawking radiation, but here is another link explaining, try to read and understand beyond where it says “this visualization is not for real particles, but virtual ones. They are calculational tools only, not physically observable entities”. https://medium.com/starts-with-a-bang/ask-ethan-how-do-hawking-radiation-and-relativistic-jets-escape-from-a-black-hole-b7a4ef7d9bdf

Just to recap on virtual particles and vacuum fluctuation, important to read and understand before diving into your QED book:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/
https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
Also some comments by Prof Baez http://physicsfaq.co.uk/Relativity/BlackHoles/hawking.html

No. They are real photons.

This statement disagrees with my text book, section on QED. I will re read the section very slowly, I do not think I have misunderstood what I read.

Are you possibly redefining what a photon is, and giving it EM characteristics?

I think you must be misreading, it would be unusual for a book on QED to mention antenna and radio waves specifically, all em fields are treated in the same way no matter what their energy. Are you sure your not looking at the evanescent field close to the antenna?
A photon does not need to be redefined to have em characteristics, they are embedded in its Maxwell equation source where a photon is just a quantisation of the em gauge field (in other words it is the field measured with a value of one quanta when detected). See first few paragraphs of: https://www.imperial.ac.uk/media/imperial-college/research-centres-and-groups/theoretical-physics/msc/current/qed/Photons.pdf

9

Guest Book / Re: Hello Everyone

« on: 28/06/2019 08:13:02 »

Hi, everyone I'm new for this place. I'm here to share my views and opinion to all of you.
Well, by profession I'm CEO of spamcommerciallink.com.

Poor attempt to advertise your food delivery service.
If you serve up spam you must be ancient roadside caf quality.
Go fry

10

New Theories / Re: New Theories: Will all moving objects with mass generate gravitational waves?

« on: 26/06/2019 15:00:34 »

Since the threads in the Alternative Theories sub-forum are not consideration as “hard science” I will say that I have seen no objection to the comment that all space is filled with gravitational wave energy, coming and going in all directions.

No objection does not mean agreement. In New Theories any ideas other than conspiracy and religious theories are allowed. Generally most of us don’t have the time to follow them all.

11

Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 24/06/2019 14:39:07 »

I'm an amateur musician when not being an artist, you simply cannot get decent visualisation software,

Takes me back to my early teenage when I made a sound to light unit. Different coloured lights for each frequency band.

Re. Pico, also a geek - so tinkering with stereo leads & probes appeals

As Alan says “Lissajous figures from raw stereo music are likely to be very messy”. You are basically creating vectorscope which is very useful in recording as you can see the phase relationship between the channels and monitor the effects of limiting.

12

Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 23/06/2019 23:02:45 »

I did wonder why you had rejected Pico as it seems ideal. Iknow some people dislike the quantisation of the levels, but the pico has enough resolution for what you need.
Like Alan I’ve used one of these - still have one in the spares box - and can agree with him that they are excellent tools.
Let us know how you get on.

13

Technology / Re: Will this 2-probe oscilloscope produce an XY display?

« on: 23/06/2019 08:22:38 »

It would need an x input sometimes labeled external timebase. There would also be a switch to change from internal timebase to external - often on the timebase selector.

By the way, I have vague recollections of someone making a box to display lissajous figures on a tv. Might be worth investigating.

PS I’m moving this to technology because it isn’t really a physics question

14

Physics, Astronomy & Cosmology / Re: Is it possible to connect a second analogue display to an oscilloscope?

« on: 23/06/2019 00:32:44 »

That would depend on whether the grid was software generated and what display options are available.
I have both Tektronix and Fluke ‘scopes and they have display options to have a border rather than grid or dot pattern; neither have a blank screen option, both are digital.

15

Physics, Astronomy & Cosmology / Re: Is it possible to connect a second analogue display to an oscilloscope?

« on: 21/06/2019 23:46:22 »

Sounds like you would be better off with an old analogue scope. The glass grid acted as a protector for the crt and could be removed to clean dust off the crt face. Usually held by a bezel you could unscrew or prise out

16

Physics, Astronomy & Cosmology / Re: Is "Space" distinct from "nothingness"? (and the Vacuum)

« on: 21/06/2019 23:26:28 »

Yes, I am afraid it is beyond me. But the 'virtual particle' is a theory, I don't see that it can be proved or disproved beyond laboratory conditions, with all due respects to Mr Arnold Neumaier.

Virtual particles are not a theory, they are representations of mathematical models of internal processes in QM. Prof Neumaier has done a lot of work on the maths of QM and is keen to dispel some of the misunderstandings that arise due to poor interpretation of the maths and concepts.
Examples abound. There is one poor soul in new theories who is completely confused by his misunderstanding of observation, measurement, wave/particle duality, matter waves etc; such that he is unable to understand some very simple concepts.

17

New Theories / Re: New Theories: Will all moving objects with mass generate gravitational waves?

« on: 20/06/2019 09:45:54 »

The force of gravity is in the proximity of the surrounding massive objects, in accord with the equations that have been developed to quantify it. So isn’t it safe to say that the cause of gravity is in the relative mass of objects, their relative motion, and the potential for their masses to cause relative motion?

We know that any form of energy bends spacetime and causes the effect we can measure as a gravitational field.
Mass is a very, very concentrated form of energy - there is a lot of energy locked up in it - so it bends spacetime more than any other form of energy. But it is the absolute masses  not the relative masses that determines the field.
Yes, the gravitational field at any point is the sum of the effects of all the masses and will change with their motion.
Short version 

18

Geology, Palaeontology & Archaeology / Re: Spam.com

« on: 15/06/2019 08:50:57 »

Well, let us assist you to travel away from this forum.

19

Physics, Astronomy & Cosmology / Re: Will all moving objects with mass generate gravitational waves?

« on: 14/06/2019 23:21:28 »

Since accelerated objects emit gravitational waves at the speed of light, and therefore gravity is said to have an ever expanding reach, it seems fair to postulate that all locations in space would contain fluctuating levels of gravitational wave energy that influence the relative motion of the surrounding celestial objects.”

I think there is a danger here of confusing 2 related but different things, the gravitational field and gravitational waves.
The gravitational field is due to a mass and gravitational waves are a propagating disturbance/oscillation of this field in much the same way that light is a disturbance/oscillation of the em field. The gravitational waves are not strong enough to influence the motion of celestial objects, but the gravitational field is.
Changes to a gravitational field (caused by a moving mass) propagate at the speed of light, but in a somewhat surprising way that means the force experienced by a test mass will always point to the current position of the moving mass rather than it’s position x light seconds ago. Below is a popsci article that explains what happens and below that I’ve compared it with a similar effect due to a moving charge.

https://medium.com/starts-with-a-bang/what-is-the-speed-of-gravity-8ada2eb08430

There are similarities between em radiation and gravity and comparisons can be made which help us to understand them better.
Let’s start with the field surrounding an electron. A test +ve charge will be attracted to the electrons position. We know that the electric field propagates at light speed, but if the electron is moving the test charge will move towards the current position of the electron, not where it was. In this way the field behaves in a similar way to gravity.
What is less well known is that if the electron changes velocity the test charge will move towards the position the electron would have been at had it not accelerated, until such time as the change in the field propagates to the test charge’s position. How does the test charge know where the electron will be? I can offer an analogy that shows that this behaviour of fields is not so mysterious.
Imagine a boat crossing a lake, the bow wave propagates away from the boat, but even at some distance from the boat the crests point to the boat’s current position (almost,  because waves in water don’t propagate exactly as do em waves). If the boat changes direction it will take time for the change to propagate to the observer, and until it does the bow wave will point to the predicted position of the boat had it not changed course.
In the case of the accelerating electron we know the speed at which the change propagates, because the change causes a discontinuity in the field which we detect as em radiation - light, radio etc (and if we have a quantum detector we can say we detected a photon).  We can describe the electron field at any point as being dependent on the history of both the position and derivative of position (velocity) of the electron.
A similar effect occurs with gravity. As @Halc pointed out, the force felt by the moon is directed to the current position of the earth rather than it’s historical position. This led early researcher to conclude that the speed of gravity was either instantaneous or extremely fast whereas it does not need to be for similar reasons as I have described for the electron.
It’s worth pointing out that the gravity situation is slightly more complex because there is a higher order effect which allows the masses to ‘point’ towards each other’s current positions despite both being in non-linear motion around a common centre of mass. This higher order effect is also why em waves are dipole and gravitational waves are quadrupole. It also means that gravitational waves cannot be produced by a simple acceleration of a single mass. However, the gravitational waves we have detected (which are analogous to the em radiation of the electron) show that the speed of propagation, and hence the speed at which gravity changes propagate, is as close to light speed as can be measured.

EDIT Whoops, @evan_au was posting as I was typing.

20

Chemistry / Re: Why Choose Full Lace Remy Hair Bundles?

« on: 13/06/2019 08:37:59 »

Oh dear, trying to spam us eh?
Well, hair today, gone tomorrow