Relativity - my brain is hurting. Help !

Hi Bill, and again, many thanks for your guidance and kind words. Now comes the awkward bit where we seem to have a different understanding...........

From the figures I have seen ( mind you, I don’t know how reliable my sources are - starting with Jim and his Paradox) the atomic clocks in the GPS satellites are affectedless by speed and more by gravity. Typical figures quoted are 7 micro seconds slower per day by speed and 45 micro seconds per day faster by gravity. The overall outcome is that the satellite clocks run faster than the earth clocks by 38 micro seconds per day. As I say, I am only repeating my interpretation of what I have read, so could easily be wrong !

Changing these 38 micro seconds into 38,000 nano seconds per day brings things into perspective. Light travels at 1 foot per nano second. For GPS to be precise, clock times need to be known to within (say) 10 to 20 nano seconds. [A 38,000 nano second timing error would translate into a 10km position error each day and continue to accumulate !]

Rather than have clocks with 38,000 ns per day differences, the satellite clocks are adjusted before launch to compensate for these predicted effects. In practice, simply changing the definition of the number of atomic transitions that constitute a 1 second interval (and consequently a nano second) achieves this aim. If the revised definition is right, the satellite clock, once in space, will count off seconds (and nano seconds) at the same rate as earth clocks.

I understand that satellites don't always achieve their predicted orbit and hence the gravity effect isn't always accurately compensated..........

Ok, there is much more to GPS than above, eg the Ionosphere affects the speed of electro-magnetic wave transmission and is frequency-dependent – hence two transmissions at different frequencies, but the old gray matter is beginning to ache again, so enough from me tonight !!

I hope you all will correct any errors in my understanding as expressed above and elsewhere. My students don’t need to know this stuff, but I am curious and would also like to get a better understanding of what makes our universe “tick”

Big Bill

I have noticed that most of your posts to this thread are delayed before publication. The Padded Cell summary page indicates that you have posted in this thread (about 23:00 UTC), but the thread is devoid of your post at this time.

I mention this in case there is confusion between posts. I hope not, but who knows !

Better than Solaris?

That reminds me.  In the mid 1970s we went to the Soviet Union for 4 days in Leningrad (St.Petersburg) and 4 days in Moscow, at about Easter time.   We flew by Aeroflop and as we were coming in to land at Leningrad, we were at tree top level but all of a sudden the pilot decided to put his foot down.  We went back up to a high level and circled around for best part of an hour before we came in to land - with absolutely no explanation.  Soiled trousers all round!

We were going through passport control etc and I had a few Sci-Fi books in my case and some officious little toad didn't like the look of them and called a soldier over, who had a mean looking machine gun - don't all machine guns look mean.  Well he wondered over looked at my books and then said in perfect English "Ah you are a Sci-Fi fan, great me too".  We then chatted for about 30min about Sci-Fi and he was really happy that I had read Solaris by Lem and really liked it.  We parted the best of friends, although my missus was having kittens.  She soon got back to her old self when I told her we were chatting about Sci-Fi - I was retrieving books from a place on my anatomy where the sun don't shine for the next couple of days.  Women Huh.

Solaris = Brilliant!

NO, if you were travelling to the stars at very high speed then you will feel no different and by your internal clock if you die at say 84 years old then by your internal clock it will be 84 years.  But if you had stayed on Earth those 84 years would have seemed exactly the same - but just a bit more boring because you didn't get to go to the stars.

If the traveller could see the people on Earth (which he couldn't, how could he?) they would appear to be moving quicker - they really would.

If you and I were born at exactly the same instance then by now one of us would be slightly older than the other but even if it was quite a bit we would not know.

You are right this stuff gives you a headache, but ain't it fun.  Who would ever have thought that the Universe could be such a fun place?

I saw a piece of film where a news reporter asked Einstein what all this relativity stuff was about.  "Well," said the great man, "imagine if you held your hand on a hot stove for a minute, it would seem like an hour.  Then imagine you have your hand on a beautiful woman for an hour, then it would seem like a minute.  That is relativity."

Not sure the reporter was any the wiser but you can see where Albert was coming from and it makes you grin!

No I am on remand, so to speak.  I told another poster what I thought about him and now my rebellious and libellous posts have to pass the sensitive eyes of the 'thought police' and they seem very slow at the moment.

You may not see this post at all, it's all relative. 

Not awkward at all!  I am not sure who is right, it was some time back when I saw the figures I refer to earlier and it is quite possible I have since mixed them up.  Thinking about it you are most probably right because in discussions on this topic people often ignore the time dilation due to increased speed and often only talk about the lessening of the distortion of space-time due to their increased distance from the Earth.

I have to pinch myself at times when I use the SatNav in the car or my wonderful Garmin Oregon 650 when out walking or cycling - now that is really some piece of kit.

Changing the subject very slightly.  Have a search round on t'internet for "Newton's Spinning Bucket" but it might make your headache worse.

THEY want you to believe this is an effect of Moderation.

Taking into account the delay between posting and appearance here on earth I calculate that BB has been sent to Io and is presently 17 years old.

I think it is an advanced feature of Hoopla. And this one works!

About my age then! 

Wikipedia 'Quantum Entanglement' has a bash at this, although gets vicously technical after a bit

Einstein famously called this 'spooky action at a distance'.

Bruce

Quantum Entanglement is meant to cover the distance of the universe regarding information of two photons Simultaneously !

My take on this is that the contemporary science used to prove or otherwise the theories of Quantum physics has taken a transparent position . It is a work in progress.    If something sounds nonsense it probably is until someone can put together a reasonable model, or someone can come up with a theory  that makes more sense of what data there is.

Some of the ways of tackling this deal with 'non locality'. Lost me but I will just try again.

Ultimately I decided you ether have a deep appreciation of this stuff through the maths or you just have vague and actually very unsatisfactory analogies that make you feel like you have the concept, when you don't. They are fun however,

The Quantum Universe is magnificently wierd. Makes my simple head feel that it cannot be true!

bruce

You've done it now!

Quantum Mechanics (QM) is not something we can understand in ways that mirror our everyday existence.  You are talking about "Quantum Entanglement of Particles" something totally bizarre only belonging to the frenzied mind of Count Arthur Strong!

This entanglement is when two particles are produced following some 'process' which go off in different directions but are linked in some of their properties and this stuff is not just theory but experiments have been done that demonstrate it.

Take spin as an example!  Photons have spin but this spin is weird, it's magnitude is always the same, the only thing that varies is the spin direction and this can be Clockwise (CW) or Counter Clockwise (CCW).  If you measure the spin the only thing that varies is its direction, you never find that it has a component in x-axis and in the y-axis and when you measure it you get an averaged figure - it don't happen.  It always appears that you are looking down the centre of rotation.  This is found experimentally.

Now if you measure the spin of one photon along an axis then if you measure the spin of the other photon along the same axis then their spin will ALWAYS be the same.  If we did the same sort of experiment with electrons then their spin will be the opposite of one another ALWAYS.  This is entanglement.

Now Einstein took the logical and seemingly consistent view that this violated Relativity because it suggests that something moves faster than light.  Einstein and a couple of his drinking buddies, commonly called EPR suggested that when the particles were ejected they were 'programmed' with  certain properties like the spin property, ie the concept of locality was upheld.  Thus QM at it's core is faulty!  QM's view was that the property of spin was 'uncertain' (Heisenberg) and thus not knowable until we measure it and thus the concept of locality does not always hold at the Quantum level.

Now to you and I the EPR view seems logical and Pauli said "Look guys, we can't measure it so why bother", or words to that effect.

But bring on the brilliant Irish Scientist John Bell, who did not accept Pauli's view and was convinced he could design an experiment to prove it one way or another and he did.  He proposed a statistical method where you construct equipment to measure the spin of the two particles at the same distance from the source and along three different alignments.   You then take a measurement along a randomly chosen axis, that is not the same alignment on both sides - but totally random.  He then calculated the statistics for a reading each side of the side being the same, for  EPR to be correct and found it to be > 0.5 (I think it was 5/9) and the QM uncertain case and found that to be < 0.5.

At this time nobody had the kit to do this experiment but 20 or so years later (I think it was 20) the experiment was run a number of times under different conditions, in fact one experiment was run where the two detectors were km apart.  The result was always < 0.5.  These experiments showed that EPR were wrong and that the spin of the particle was not knowable until it was measured.

Now I don't think at the moment that there is a theory that can explain why this happens but subsequent work have shown that entanglement is in fact central to QM and some theorist have proposed that from entanglement we can explain what time is and how & why it flows the way it does.

NOBODY has ever proposed that it violates Einstein's great work!

Return From The Stars is not better, but I found it more enjoyable to read. It may be down to the translation, I think the copy of Solaris I read was translated from French to English having previously been translated from Polish to French. There are overly long sections of completely boring text, descriptions of take off and the surface of Solaris spring to mind.

I doubt the Russians appreciated The Cyberiad, the leaders and governments of planets are obviously allegories of the soviet leadership/system.

Bruce is quite right that being able to follow the maths of relativity (either type) does make understanding it a whole lot easier. It's still a bitch from an intuitive point of view though.

I'm only checking the forum every few days at the moment, so this is going to be a tidy-up post, as it were. Bear with.

Don: Every type of clock (atomic, wrist, biological) runs slow from the point of view of an observer moving at a different speed to the clock in question. This is 'simply' because time is running at different rates in the two points of view. In the twin paradox, it seems at first that each twin's point of view is exactly equivalent to the other, and two people cannot each be younger than the other. The solution to the apparent paradox is that the twins' points of view are not exactly equivalent. The twin who has travelled on the rocket must have accelerated at several stages in his journey, whereas the twin who stays on earth does not. Therefore, the travelling twin ends up younger than the earthbound twin.

Hook: Hafele and Keating's experiment did not produce a novel result for physicists, though it is sometimes presented as such. It was simply done because atomic clocks had finally been made which could be transported easily on a plane and was therefore a nice thing to do. The predictions of special and general relativity had already been confirmed and reproduced countless times by 1970 - all Hafele and Keating were doing was showing relativistic effects in a very immediately understandable way. If you're interested, their original paper is:

I have seen programmes where scientists claim that electrons, not photons, "know" the energy state of every other electron in the universe immediately.

They have equations that "prove" this. They cannot, however, demonstrate that the equations are true in real life.

I can't get my head around this idea of entanglement. How can one particle of an entangled pair know that a measurement has been performed on the other? First of all, I like to think of measurement as a passive activity, and not something changes what's being observed. Also, how are these particles communicating? At the time one is being measured, the other can be far, far away. Do they have little tiny wormholes connecting them? How do they know? 

It reminds me of the paradox of the thermos. You put cold water in, it keeps it cold. You put hot water in, it keeps it hot. So how does it know? 

Also, the whole Shrödinger's cat thing also creeps me out. Alive and dead at the same time? I say let the poor half-dead thing out of the box!

Of course, when you did finally let the cat out, it would enter the third state........Bloody Furious!*

*with apologies to Sir Terry Pratchett.

It is a fundamental principle of the theory of quantum physics that the act of observation is not passive, it affects the characteristics of the observed particle. In essence it affects reality!

This is not just via the uncertainty principle (whereby the more precisely one variable is known momentum, the less precisely other can be known ie position) but a direct effect of observation. It is not because the act of detection influences the physics of the system either-it occurs with an entirely passive and unconscious detector.

In my head I have always thought of this as forcing the probabilistic nature of the observed particle to 'make up its mind' and default to a specific state. Without/before observation it exists in multiple potential states. The cat is not just either alive or dead, it is both, (and neither) until we observe it.

I hope the more technical minded members of the forum don't wince at this attempted explanation!

Bruce

Bruce I like the cut of your jib and find your explanation enlightening.

When we discuss QM we have always to remember what Ebor said above that these things are found by experiment, not just what pours out of the math or some nutters brain.  They are real and observed.  So unless we want to (and are able to) show that these experiments are faulty then we have to accept the results.

Also we cannot explain QM in ways that fit in with our view of reality.  We have to accept that QM shows us that our everyday view of reality is false or we could simply ignore these experiments.  The choice is yours.

Let me talk about another series of experiments.  We fire a beam of photons (or electrons) at a plane at a right angle to the beam which has two small slits where we target the beam.  Then behind this we have a detector.  We then let the experiment run for a while, what do we find on the detector?  Well we find two places where the photons have gone straight through the slits, exactly what we would see if we had done the experiment with golf balls and bigger slits of course,  But we also see bands in between and these are caused by the fact that the photon beam starts to diverge as it leaves each slit and the inside edges of each beam actually merge and interfere.  Now if at a point the beams are in phase (ie sine wave in phase) then we get a signal on the detector, whereas if they are out of phase they destroy each other and we get darkness (not the band The Darkness I hasten to add).  Between these two extremes we get some signal, which is less than fully in phase but more than nothing.  We call these bands in between the two main points 'Interference Fringes'.  This is not a surprising result because photons of light can be thought of as a wave motion.  In fact I remember when I was young a Physicist ranted and raved at me for even suggesting that photons were more than some mathematical construct.  They were to be thought of as a wave motion only!  This was late 60s early 70s, so he should have known better!

Ok, so well and so good.  We now repeat the experiment with an electron beam, these little chaps, unlike photons, have mass and so will behave like our golf ball thought experiment - SURELY!  Err no they don't, they give exactly the same result as photons, ie we see interference fringes.  So in the microscopic world of the electron we find a duality of matter, mass and waveforms at the same time.

So we stop talking about golf balls , stupid game anyway.  Lets do the experiment with a photon source that emits a single photon only at any one time, so only one photon will hit the slits at any one time.  It will therefore, have to go through one slit or another.  So we cannot get interference.  Hey I am beginning to think about golf balls again.  So we run the experiment again and we get interference fringes!  WHAT how can this be, the photon is interfering with itself (sorry Mr Moderator sir), surely not.  But yes that is what we see and this happens because the photon is in fact a Cat, in fact it is Schrodinger's Cat.  Until it is measured on the detector it momentum and position are not knowable, as it passes though the slits it has a probability > 0 of passing through either slit.  So what we are seeing on the detector is a probability wave.

OK this little sucker is bugging me, lets find out which slits are being traversed, I can't believe this Cat thing.  So we put a detector on each slit and run the experiment again.  We find that we detect the electron in one slit only and more shockingly we get no interference at all.  The mere act of measuring has collapsed the probability wave down to a value of one in one slit or the other.  Golf anyone?

A little footnote

The brilliant Richard Feynman had suggested at one time that there is in fact only one electron in the whole Universe and I think he was partly serious!

Personally I don't find the vagaries of QM to be that strange.  After all loads of people on this planet believe that when you die, something flies out of your body containing the essential you and goes to a place that does not exist in this physical Universe.  The boss of this place looks just like us but has a big white beard.

btw I have a big white beard!

When you see programs about QM they always jump straight to stuff regarding Uncertainty and that annoys me in a way.  Jim Al-Khalili in his last TV program gave some applications of Uncertainty in Biology but they were insubstantial, throw away things.  Not only that but applications is an odd word to be used.

I would like one of these programs to show how QM totally revolutionised Chemistry.  It is impossible today to study Chemistry without referring to QM.  It explains why certain compounds are coloured (Spectroscopy), why photosynthesis works (needed more detail the Jim), why atoms join together to form bonds, etc etc.  Oh and btw it was Spectroscopy that enabled us to make the statement that the Universe is expanding.  This is just a very small list of QM's achievements, the complete one is much bigger and that is in a way, its problem.  If QM was not so successful we could just ignore its wackiness and go back to thinking about electrons looking like planets orbiting the Sun.  Trouble is that theory never worked but QM does.

Can't argue that QM hasn't been successful.  Scientists have discovered smaller and smaller stuff, and there's a huge body of applied science based on QM. But as technology advances, I do wonder how our understanding of the very small/new (and the very large/old) will change in the future.

I've read about shooting a photon through two slits at once. I can almost grasp the theory that if we try and observe it, the photon's wave function will collapse, the quantum effect will cease, and the proton will no longer be seen in two places at once. But if the uncertainty principle calls into question whether or not a photon can ever really be observed at all, then why do we trust the results of this experiment? Are there any competing theories to explain the results, or is the debate within the QM community over?

Also, I remember reading that QM and GR are in conflict, and that a unified theory can never be base on QM alone. Is that still true?

Bill - given the Santa beard, you really should post a picture to the selfie thread! 

I also liked Terry Pratchett's take on the Big Bang, in the 1st Discworld novel I think.

Nope, no selfies sorry, I just hate the concept!  Probably because I am too ugly or the fact I shave it off just before xmas.  No don't laugh, my missus does a day a week at Age Concern and she gets me to come to their xmas party dressed as Santa and hand the presents out.  You will be amazed at what some of these old biddies ask for their xmas present.

Of course QM will change.  Planck's original idea was only a smidgen over 100 years ago and since then QM has given us brilliant results and it still goes on evolving.  I get really angry when people say that Christian Science, Spiritualism or Creationism (+ others) should be treated as a science.  Are they prepared to throw everything they believe in if something that fits the observable facts better comes along.  Of course not, they all have a central dogma but Science has no dogma.  Individuals may want to hold onto to their favourite 'things' and may become dogmatic but not Science as a body!  Blimey I have been to enough conferences in the past where people have stood toe-to-toe trying to shout each other down.  I have even seen a discussion end up in fists, unfortunately not often enough though!

The thing is Hook we have to trust the experiments, we can't substitute faith for experimental evidence.  I remember Richard Feynman saying how science works:

(a) Invent a theory, just think up any old rubbish,

(b) think up some experiments to test this theory, and

(c) if the experiments disagree with the results from theory then start the process again, otherwise get your best suit cleaned for the Nobel Prize ceremony.

It's that simple and no the debate within QM is not over and will not be for a while.  I remember when String Theory was first raising its head and people were saying it's the end for QM.  NO!

But if something new and radical appears science will throw away QM, just as it would Darwinism.  My thoughts are that in 100 years QM will still be around but hardly recognisable to that of today.

It's like any other field.  I can well remember when XML first appeared and my first impression was great an end to interchange files that have no real standards, eg CSV, dBase .dbf files, .ini files etc.   And yes XML was far superior to these file types but very soon people were saying to me HTML is dead, XML will replace it.  What a claim to make!  XML was never intended to replace HTML but rather to sit next to it and that was what happened.  I never knew just how people got the wrong end of the stick but so many did.  I suppose it was because it was presented as an Internet technology, which is of course not true, it makes a great replacement for .ini files.

Relativity v Quantum Mechanics.

The Universe is the way it is.

We don’t know the way it is, nor why it is the way it is.

We have performed experiments and described theories, sometimes encompassing predictive mathematical formulae, to help us understand the “ways” (science ?) and the “whys” (religion ?) of the Universe.

Within reason, some of these theories about the “ways” of the Universe enable us to predict the outcome of future events and human activity. Examples include the time at which trains will arrive or pass each other, the bending of an aeroplane wing, our location on the side of a mountain. We use these quite successfully in our everyday lives.

We don’t know how much more of the “ways” there is to understand. We know that there are inaccuracies in some of our pragmatic formulae, but nevertheless we use them because they are useful and accurate/predictable enough. We are aware of inconsistencies and incompatibilities between our various theories but we use those parts that are useful and continue to search for more compatible theories.

We know that just because Theory X predicts outcomes A and B, and we are confident that outcome A actually happens, there is no guarantee that outcome B will also happen

Sometimes we agree its just nice to know things, even if there is no obvious practical use for this knowledge at present.

We also like to discuss, or even argue, with each other about the relative merits of Theory X and Theory Y. That’s one reason why the Padded Cell was invented.

The Pope and the Archbishop of Canterbury can discuss the other “whys” of the Universe.