81

Physics, Astronomy & Cosmology / Re: Observation = Information = Quantum Entanglement?

« on: 19/11/2017 15:16:54 »

Which makes sense according to Einstein, because they are travelling so fast that they don't experience any time at all. To them all events happen instantaneously. The entire universe, to a photon, is instantaneous.

I don’t think Einstein said that, but opinions are divided; quot sapientes, tot sententiae.

It is fascinating that one physicist can say categorically that photons don’t experience time, but another can say the opposite. The way I understand it goes something like this:

Special relativity provides for an inertial frame for everything that has mass, but it does not cover massless particles such as the photon. Talking of the photon having a frame of reference is, strictly speaking, not scientific. The photon must always be observed as travelling at “c”. It cannot be at rest relative to anything. Of course, one could argue that it must be at rest relative to itself, but that is not a very productive line of reasoning. Science has not actually produced definite proof that the photon cannot be assigned an inertial frame, but to maintain that it does have one is pure speculation, and maintaining that it does not have one seems to be the generally accepted position.

Taking the time dilation equation to its ultimate conclusion may seem a logical thing to do, but it is not supported by special relativity because of the lack of mass of the photon which puts it outside the remit of special relativity. It seems that the best we can say is that we have no way of knowing if photons experience time, or not. Nor do we have any scientifically accredited theory that covers this, nor any way to test the idea experimentally, as no massive object can reach the speed of light, and a clock cannot be fixed to a photon.

82

Physics, Astronomy & Cosmology / Re: If I moved backwards at the speed of light holding a torch, what would happen at the start of th

« on: 19/11/2017 13:49:49 »

My own speculations would be of far less interest to another person than the speculations of someone with  learned knowledge and experience.

Not necessarily. Just because someone has a lot of knowledge in a particular area does not mean that he/she can always use that knowledge to the best advantage, or draw the "best" conclusions from it.  Don't undervalue your own efforts.

I spent much of my early childhood deep in the Cornish countryside.  I still retain "pearls" of wisdom that came from people who could hardly read or write.  One of these was:  "Never pretend to understand something you don't really understand: and never believe something unless you understand it".  OK, one can pick holes in that, but it contributed to my being known as "What if", because I questioned everything.  (Not aloud, if they happened to be my mother's edicts )

83

Physics, Astronomy & Cosmology / Re: Observation = Information = Quantum Entanglement?

« on: 18/11/2017 19:40:19 »

Fascinating thread. Lots to think about. No time to chip in at present, but hope to return. 

This has to be among the better conducted discussions, Right or wrong; ideas are well presented, and thread drift kept to a minimum. 

84

Physics, Astronomy & Cosmology / Re: Is it possible to define infinity?

« on: 10/11/2017 18:33:52 »

Bogie_smiles, I'm not ignoring your post, but am finding breathing (and thinking ) a bit difficult today, and want to be able to do justice to your points.

I might look for some "reprise" points as an easy option, and to try to stop them from slipping into oblivion.

85

Geology, Palaeontology & Archaeology / Re: Is Mt Everest the tallest mountain on Earth?

« on: 07/11/2017 23:39:24 »

E.g.: Mt Everest is NOT the farthest point from Earth´s center.

Nor is it the tallest from base to summit, if you include submarine examples.

86

Question of the Week / Re: QotW - 17.10.29 - Is it safe to be in a car during a thunderstorm?

« on: 05/11/2017 18:31:34 »

Some good, sound advice here, but it is worth remembering that on the road in a storm, especially in heavy traffic, your chances of being hit  by lightning are vanishingly small compared with the chances of being hit by, or hitting, another vehicle.  My reaction would always be guided by the road safety aspect.

87

Physics, Astronomy & Cosmology / Re: How would the universe change if the speed of light increased?

« on: 05/11/2017 12:35:25 »

Bill, I Sincerely Apologize. 🌷

Thanks, Zer0.  No one expects you to be a mind reader, but checking with fellow posters before playing silly b*ggers with their names might be considered a matter of courtesy.  No lasting harm.

I hope we can continue to have interesting exchanges.

88

Physics, Astronomy & Cosmology / Re: How would the universe change if the speed of light increased?

« on: 31/10/2017 20:16:56 »

Zer0, I applaud your imagination. What else can one say? 

Do you want to tackle these points seriously?  If so, we might need a slightly different approach.

89

Physics, Astronomy & Cosmology / Re: Why is Space considered as a Void/Empty/Vacuum?

« on: 26/10/2017 21:49:58 »

one can scientifically conclude there is absolutely no void or vacuum or emptiness in space.

I would not argue with that, but it is worth remembering that linguistic usage is such that words like “void” and “vacuum” can be, and are, used by scientists in specific ways, such that they don’t always imply “emptiness”. 

Just think of the ways in which “nothing” is used. 

One of my favourite quotes is from Lawrence Krauss:  “By nothing, I do not mean nothing…..”

90

Physics, Astronomy & Cosmology / Re: Why is Space considered as a Void/Empty/Vacuum?

« on: 23/10/2017 18:45:34 »

Returning to the OP:

Christophe Galfard (The Universe in Your Hand) says:

“To appear, particles have to borrow some energy from the quantum fields,  And since those fields fill in every place in space and time.  Particles can literally appear anywhere, and anytime.  That is the reason why there is no such thing as true emptiness, anywhere in the universe.”

Initially, I found this book off-putting, but much later, I decided to give it another go.  I’m glad I did. I would recommend it to absolute beginners.

91

Physics, Astronomy & Cosmology / Re: Why is Space considered as a Void/Empty/Vacuum?

« on: 22/10/2017 11:52:14 »

Could be the tendency to think in terms of physical curvature is part of the problem.   Spacetime is not curved within some higher dimensional medium.  What we think of as curvature (for convenience, and because the maths works) is a situation which makes one direction special, as compared to other directions.  Viewed that way, the question of emptiness, or otherwise, is not a problem.

An even more extreme case exists with black holes - the path of passing light can be bent so severely that the light orbits 2 or 3 times around the black hole before continuing onwards to reach us!

If gravity is strong enough to cause light to go into orbit, what might change to allow it to escape?

92

Physics, Astronomy & Cosmology / Re: How would the universe change if the speed of light increased?

« on: 09/10/2017 21:39:43 »

Thanks for the good wishes, Zer0.

My very inexpert opinion is that your conclusion is absolutely right; the beam that was deflected round the sun would take slightly longer to reach the Earth, because it would have to travel a little further than the other beam, at the same speed.

With a little adjustment, your question would provide a simple, if somewhat protracted, example of gravitational lensing. 

There are those experts who interpret the effects of gravitational lensing as evidence of other dimensions or, even worse, of past directed time travel.

Jenny Randles seems to favour both, explaining gravitational lensing round a cosmic string she says of two light rays, separated by gravitational lensing, and arriving at different times: “One will travel less distance thanks to the presence of the cosmic string.  However, it has still traveled at the same speed as the other ray of light despite reaching its destination early.  Although we cannot view the motion of this light ray through those dimensions hidden from us, it seems to our senses that one of these rays has traveled faster than light.”  She goes on to say: “That speed is an illusion caused by the shortcut, but explains how it can arrive too early.  It will travel so fast, it will experience time travel and have actually moved into the past.”   

Ref:  Randles, J.  "Breaking the Time Barrier"

I’ve done my best to make sense of that, but the feeling that it is “fairy tale physics” just refuses to go away.

93

Physics, Astronomy & Cosmology / Re: How would the universe change if the speed of light increased?

« on: 08/10/2017 21:48:05 »

I've spent the last couple of days in Hosp with a scull fracture; a small one, not enough to let in any sense, so if my posts are more ridiculous than usual, I have an excuse. 

Hi Zer0, welcome. 

When a ray of Light enters another Medium, say from air into water it affects the Speed of light decreasing it by a very very small fraction.

When passing through a medium, photons may be absorbed by the collective vibrational modes (phonons) of the ions and electrons that form that medium.  It is then converted to heat. 
If the vibrational mode of the specific phonon doesn’t match the frequency of the photon, it “attempts to absorb”, then it (the photon) is re-emitted with a very slight delay. 
If you reason that the photon; in whatever form it takes while it is being “sampled” by the phonon; is not actually light, then the speed of light through that medium is just the sum of the times during which it is travelling between “samplings”.

Does the above statement make any sense scientifically?

It does, in that it represents the usual “shorthand” way of expressing what happens when light passes through a medium.

94

Physics, Astronomy & Cosmology / Re: Would an anti-matter black hole bend space in the opposite direction?

« on: 01/10/2017 14:40:40 »

  For elementary particles something else must be the case.

Two thoughts come to mind:

1. If the antimatter particle annihilates with one of the matter particles, the energy must still remain within the BH, so its matter/energy remains unchanged.

2. Since the BH "singularity" is shorthand for a situation about which we have no information, and in which, as far as we are aware, our current theories no longer apply; the best we can say is "dunno". 

95

Physics, Astronomy & Cosmology / Re: Do virtual photons exist?

« on: 15/09/2017 18:39:59 »

Matt Strassler says this of virtual particles at:

https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/ 

“The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle”.

The whole thing is worth reading.

96

Physics, Astronomy & Cosmology / Re: Is it possible to climb out of a gravity well with less than escape velocity?

« on: 03/09/2017 19:49:18 »

Thanks, Jeffrey. I'll not pretend to understand all the maths in the link, but I get the idea.

This seems to fit with Chris Baird's comments:

"In general, singularities are the non-physical mathematical result of a flawed physical theory. When scientists talk about black hole singularities, they are talking about the errors that appear in our current theories and not about objects that actually exist."

http://wtamu.edu/~cbaird/sq/2013/09/13/does-every-black-hole-contain-a-singularity/

97

Physics, Astronomy & Cosmology / Re: Is it dark because of the absence of light or it is dark because of its nature?

« on: 20/08/2017 21:50:15 »

This seems like a rewording of the old question: Is darkness the absence of light, or light the absence of darkness. 
Put that way, it becomes obvious that light is the “tangible” thing, and if there is none about, things are dark.   

Black is simply the name we give to something that doesn’t emit or reflect light. 

….. but only noticeable when there is no light?

My mother told of a hymn she met as a child.  It contained the line: “Well he sees and knows it, when our light grows dim.”
She heard this as: “Well he sees a “nosit”, when our light grows dim.”
She wondered what a nosit was, and why anyone would see better if it grew dim.

I guess that would be called a mondegreen, these days.

98

Physics, Astronomy & Cosmology / Re: Is it possible to create gravity using magnets?

« on: 19/08/2017 20:54:45 »

That’s a great answer, Evan. The only point with which I would take issue is:

“Will it attract matter as does Earth?”
“No.”

Surely, it would attract matter, but that would be by gravity, not magnetism.  Of course, we all knew that was what you meant, but we pedantic pests can’t always resist chipping in.   

99

Physics, Astronomy & Cosmology / Re: How does time work?

« on: 06/12/2016 14:53:03 »

Nilak you are obviously aware that a snapshot of the Universe is a physical impossibility,  but it is something that is frequently used by experts,  notably by Barbour and Deutsch. That's fine as long as we always remember it's only an analogy. So is PP's motion blur, beautiful as his picture may be.

100

Physics, Astronomy & Cosmology / Re: Is spacetime real?

« on: 26/09/2016 20:16:36 »

Having drifted into talking about particle spin, this might be worth looking at.  I’m not always happy with the answers here, but this seems not bad.

http://www.askamathematician.com/2011/10/q-what-is-spin-in-particle-physics-why-is-it-different-from-just-ordinary-rotation/