tim.tdj

2 minutes ago, koti said:

Single parity bit check is the most common error detection method in hard drives that I know of. Also check error handling which is a different concept from detection. Normally hard drives loose capacity due to error occurance (bad sectors) as far as I know there are error detection and correction mechanisms built into HDD's since the first PC days, my 286 XT machine in late 80's had a 20 megabite HDD (which needed to have it head parked btw) with some sort of error detection and correction. Nowdays all the drives have complex multi level error detection and correction systems. You seem to be asking if its possible for a specific method of HDD error detection/correction to fail and the answer is always yes, everything can and will fail if used long enough under load. 

Hi Koti

Thank you very much indeed for all your help. I have just one more question:

If I was to create a RAID 1 array with four hard drives and I was to use the btrfs file system, do you think that this would be pretty bulletproof against data corruption or can you see any potential flaws in this set-up?

4 minutes ago, koti said:

Most RAID 1 systems use error detection built into the hard drives themselves. If a drive in the array reports an error, the RAID rewrites data from the other disc.

Hi Koti

Thank you.

Do you know if there are any circumstances whereby an error (such as a single bit flip) can develop on a hard drive without the hard drive detecting it? Or do all of the latest hard drives use mechanisms such as checksums to detect errors?

1 hour ago, koti said:

If an error occurs in one of the copies, it substitutes the bad data with the remaining good copy - not the other way around.

Hi Koti

Thank you very much for your reply.

I was not actually meaning the other way round.

Can RAID 1 systems detect all types of errors that can occur on a disk or are there some types of data error it can't detect and therefore wrongly think it is the correct data?

1 minute ago, koti said:

In simple terms; if you have 2 drives 1Tb each and array them into RAID 1 you will end up with 1Tb of usable space - each sector will be mirrored so if you have a bad sector on one of the drives youre good as theres a copy of that sector on the other drive. The array does not rebuild in such a manner that it could use a bad sector as usable data, thats the whole idea behind RAID 1 - redundancy. The mirror can be done or 2 or more drives (more redundancy)

Hi Koti

You seem to be implying that the RAID 1 system can always detect if it is attempting to read data from a bad sector and if this is the case, it will get the data it was attempting to get from the other disk instead. Am I correct?

13 minutes ago, koti said:

You are right, both of these statements cannot be true for RAID 1 and this one is not:
 

Thhe above is true for RAID 0 (stripe), for an array of drives in RAID 1 it will stay functional as long as at least one HDD is functional:
https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_1

Hi Koti

Thank you very much for your reply.

It has just occurred to me that a hard drive in a RAID 1 array can possibly remain "functional" in the array even when it has some bad sectors and that file corruption due to bad sectors can spread when RAID 1 arrays are rebuilding after a hard drive has been replaced. Is this true?

Hi Everyone

I have read that RAID 1 arrays work in such a way that when a file is copied to a RAID 1 array, it is copied to all of the hard drives in the array simultaneously. In other words, it is not copied to just one of the hard drives and then copied from this hard drive to the others.

I have also read that if a bad sector occurs on one hard drive in the array, the resulting data corruption can spread to the other drives.

What I don't understand is how both of the above statements can be true at the same time because how can the corruption spread if data is not being copied between the hard drives in the array?

Thank you very much.

Kind regards

Tim

14 minutes ago, swansont said:

I don't have that information.

This is a place where you can communicate with experts, but in this case it should be in the form of questions, rather than vague proposals to be disassembled. The latter is difficult to do in a way that you will understand if you are not already literate in the field you are discussing. Just saying "No, that violates conservation of angular momentum" doesn't mean much to someone who doesn't understand what angular momentum is and why one would expect it to be conserved, along with all of the esoteric details that come along if it happens to be an issue within quantum mechanics.

We end up having to explain all of that, and a discussion board is not the best format for that. Better resources exist. Universities put lectures online. There are video series (e.g. Khan academy).

I do. And those questions you want to ask them you can ask here. But that's not the same as reading about some idea, like wormholes being a connection within entanglement, and running with it.

 

Indeed.

You can't expect to  jump into the deep end and have things go well if you haven't learned how to swim.

Hi Swansont

Thank you very much indeed for all your help. I will have a look at the Khan videos.

32 minutes ago, swansont said:

That's not what we do here, though.

Hi Swansont

If this is not the place where non-experts such as myself can communicate with experts such as you in order to explore ideas such as mine to find out how plausible they are then can you point me to another forum on the Internet which serves this purpose?

The fact is that, because of events in my life beyond my control, I do not have any direct access to academic expertise. Such access is the privilege of the few. Without the support of academic expertise, it is very difficult for me to develop my ideas and to verify that they make sense to the scientific community. I find this deeply frustrating because I am insatiably curious about this sort of thing. Just watching scientific documentaries and reading science articles in magazines and on the Internet is not enough for me. Sometimes when I am listening to the scientists speaking on these documentaries or when I am reading what they have said in the articles, I often want to ask them various questions. Sometimes I have sent them very polite emails asking them the questions I wanted to ask them but the vast majority of the time, I have never received a reply. Can you understand my frustration?

I would, however, like to point out that I am actually deeply appreciative and grateful for the time that you and your colleges on this forum have all given me with this with your expertise. Thank you very much indeed for this.

1 minute ago, swansont said:

Speculating requires more rigor than you have supplied. A lot more than just tossing out some terminology and coming up with an analogy. We need some combination of an actual model, some specific predictions, and/or evidence that your idea is correct.

The fact that you are building on an unconfirmed proposal weakens your case. And from what I can tell, your analogy is not consistent with that proposal. The wormhole would facilitate communication, not travel of the particle.

And relativity/simultaneity isn't typically an issue here. It doesn't matter who measures the state first. Simultaneity is only an issue of you are trying to confirm that the correlation exists faster than could be communicated, and you can set up your experiment so that simultaneity isn't an issue. If simultaneity is an issue, then you will have trouble doing that specific test.

 

 

 

Hi Swansont

Thank you very much for your reply.

I fully realise that what I have proposed is not a sharply defined model and I have no way of obtaining any evidence that it is correct. I am merely exploring a possibility. I expect that many important scientific ideas have emerged as a result of, at first, taking the first few tentative humble baby steps which is what I am doing here with this analogy.

13 minutes ago, swansont said:

And from what I can tell, your analogy is not consistent with that proposal. The wormhole would facilitate communication, not travel of the particle.

The "spinning coin" in my metaphorical analogy is only meant to represent a piece of information or mechanism which gives information to the entangled particles at either end. It is not meant to represent an actual particle which can travel through the wormhole.

3 hours ago, Eise said:

No, you did not misinterpret me. And 3. is the case, more or less. The problem with QM is that it does not obey the logic we are used to when working with macro, i.e. classical objects. On one side, as long as a quantum particle does not interact with other objects (particles or measuring devices) many of its properties are not (exactly) determined. On the other side (within the bounds of the Heisenberg Uncertainty Principle), some conservation laws apply just as rigidly as in classical mechanics, like conservation of momentum, angular momentum, energy, etc.

Applied to entanglement: in the first place one must create an entangled pair of particles. Here is the 'Something else causes A and B' part. Classically, one would be ready with this: the particles have exactly the same value for some observable, (or exactly the opposite depending on the property you are observing, or the way you entangle the particles), because the particles have this property that is observed. But in QM that is not the case: the exact values of what you observe are only definitely determined at the moment of measurement. But still the conservation laws must hold. And this leads to the classically not understandable situation that on one side the measurements are correlated, but are not (completely) fixed by some property that the particles posses in themselves. And even stronger, and this makes the weird situation empirically provable, QM predicts a stronger correlation than all possible classical theories.

Hi Eise

Thank you very much for your reply.

After reading what you have said and also reading about the "wormholes" or "gravity channels" mentioned by other people in this thread, I think that I may have managed to combine what you have said and the "wormholes" into a metaphorical analogy about what I think may be going on. I hope you don't mind me speculating here.

Firstly, I get the impression that the most important concept that you mentioned was the conservation laws.

Here is my metaphorical analogy: Imagine that there is a coin spinning fast in such a way that the axis of its spin is exactly half way along a "wormhole" between two entangled particles. When one of the two particles gets "measured", the coin stops spinning and gets sliced along its edge and the "head" of the coin emerges from one end of the "wormhole" and the "tail" of the coin emerges from the other end. Hence the correlation. This therefore preserves the laws of conservation.

One remaining problem with this is that according to Einstein's relativity, absolute simultaneity does not exist. This means that there will be times when both particles are measured close enough together in time that there is disagreement as to which of the two particles was measured first. I think that the solution to this is to ask the following question: "Which particle was measured first from the perspective of the wormhole?" Another way of putting this is as follows: "From which end of the wormhole was the "spinning coin" measured first?"

How plausible do you think my metaphorical analogy is?

EDIT: Can you see any problems with it?

2 hours ago, Eise said:

Quantum entanglement does not 'work'. Sounds maybe as nitpicking, but it is not meant like that.

'Working' generally suggests a causal relationship. But there isn't one in entanglement. FTL is not just FTL, it's also 'FTC': faster than causality. Entanglement is a relationship of correlation. It means a.o. that it is the way nature is, not how it works. 

In my opinion there can't be an answer, because there simply is no way that entanglement 'works'. Entanglement follows directly from the formalism of Quantum mechanics, and so was derived before it was empirically proven. 

Hi Eise

Thank you very much for your reply. However, I'm afraid I don't understand it.

As I see it, if two things (A and B) are correlated then at least one of the following three statements is true:

1. A causes B.

2. B causes A.

3. Something else causes A and B.

What you are saying (correct me if I am wrong) seems to suggest that in the case of quantum entanglement, none of the above three statements are true. Have I misinterpreted you?

1 hour ago, Itoero said:

The ER=EPR conjecture states that entangled particles are connected by a wormhole. And according to MIT physicists by creating two entangled black holes, then pulling them apart, you form a wormhole. Such a wormhole might enable FTL communication. But it's a big 'what if'. http://news.mit.edu/2013/you-cant-get-entangled-without-a-wormhole-1205

Hi Itoero

Thank you very much for your reply. Sounds like a very interesting idea.

2 minutes ago, swansont said:

If there is no means to test it, it will always be hidden. QM already indicates that there are some things that we cannot know.

2 minutes ago, Strange said:

If we come up with some more "fundamental" theory, then you will still be able to ask "how does that work". So no, there will never be any "ultimate answer"; there can't be.

Hi Swansont and Strange

Thank you both very much for your replies.

7 minutes ago, swansont said:

That's not really a question of quantum mechanics, since QM is our description of how nature behaves. Not some behind-the-scenes view. Similar to how we don't have a description of what the universe looks like from the point of view of a photon, since we can never move at the speed of light. Our determination is limited to what we can measure. 

So we are not in a position to know how this "actually works" — that's a metaphysical question. What we do know is that the states are undetermined until measured, and as they are correlated, you only need one measurement to determine the states. 

Hi Swansont

Thank you very much for your reply.

So I guess that we do not currently have the means to answer this question. Do you think we ever will be able to answer it or do you think that there is some sort of fundamental barrier that will always be in the way of the answer?

Hi Everyone

I would firstly like to start by saying that I fully understand why us humans are not able to use quantum entanglement for FTL communication. It is because we can't force an outcome without breaking the entanglement and we can't detect as soon as a measurement has been made at the other end.

My question is this: Does quantum entanglement mean that the Universe itself has privileged access to a means of FTL communication for its own administrative purposes? (I can't see how quantum entanglement would work otherwise.)

Thank you very much

Kind regards

Tim

28 minutes ago, swansont said:

Yes, I can see that. But it is still A reference frame, not THE reference frame. One of convenience, not necessity.

There are many situations where one reference frame is convenient to use, but it doesn't mean you have to use it. 

Hi Swansont

Thank you very much for the clarification.

12 minutes ago, studiot said:

No I didn't say the spacetime block was radical, I said the idea of pre drawing something on it or in it was radical.

I even empahsised the 'pre'.

Pre means 'before.', usually in time but also in other contexts such as sequence.

Sorry, I misunderstood. Yeah, I agree with you that the idea of everything that we have ever experienced being prewritten into the Universe is a very radical idea because it is all so complicated and intricate. It might be the result of mathematics which are way more complicated than the mathematics that produces the Mandelbrot Set. It implies we are living inside mathematics. Anyway, remember that as I mentioned previously, I am being a devil's advocate about the SpaceTime Block concept as I don't personally believe in it. I might be wrong though.

4 minutes ago, studiot said:

This is a representation not the reality.

What we perceive might be misleading . "Reality" at the most fundamental level might be be much closer to the representation I mentioned than what we perceive.

5 minutes ago, studiot said:

 

     If they were 'predrawn' then they have a separate existence from what they are drawn on.

 

I don't know if the analogy of ink on paper can be extended this far. The events prewritten into the SpaceTime Block (if that is really what the Universe is) would be an integral part of the SpaceTime Block, they would  not be separate from it.

15 minutes ago, studiot said:

Predrawn also implies something rather radical.

I agree that the SpaceTime Block is a pretty radical idea.

12 minutes ago, studiot said:

How is a timeline 'outside time' ? 

Hi Studiot

The timelines themselves are not outside time. The hypothetical perspective i mentioned from which we are viewing it is outside time. It is like looking at a piece of paper with a graph with an x axis and a t (time) axis. By looking at the piece of paper, we are outside the time represented by the t axis because we can see the whole of the graph at once.

12 minutes ago, studiot said:

What I am saying is that there is a state or situation in which you could (in principle) hold both particles in your hand together.

And there is another state where you could only hold one of them.

And since you could observe both states

1) Change exists

2) What we call Time must exist to permit this. 

Your two particles would be represented by two lines of different lengths drawn on the piece of paper I mentioned above which represent the different lifespans of the two particles. This drawing does not change.

The debate the scientific philosophers are having is whether the Universe at the most fundamental level is like the unchanging piece of paper with unchanging timelines predrawn on it or the Universe is as we perceive it (we perceive it changing).

10 minutes ago, studiot said:

 

Well that's easy then.

Consider two c- existent sub atomic particles, one with a significantly longer life than the other.

When the shorter lived one expires, the relationship of co-existence ceases.

 

Hi Studiot

Very interesting reply.

From the perspective outside of time (I am being a devil's advocate here because I don't actually believe in such a perspective), this can be seen as two time lines (one for each particle) where one line is shorter than the other. From the perspective outside of time, these lines do not change.

57 minutes ago, swansont said:

That tells you if you are at rest with respect to the CMB. You can do that for any two frames of reference. It will not tell you if that rest is absolute. That would require that physics itself behave differently in that one frame. Doppler shifts still follow the same formula, so they are not evidence of an absolute frame.

Hi Swansont

Thank you very much. You have made it somewhat clearer. What you seem to be implying (correct me if I am wrong) is that the CMB is not as much of a fundamental entity as I am thinking it may be. (I expect that you can probably see why it is very tempting to view the CMB as being the basis for a preferred reference frame.)

I think that we basically need to wait until more laws of physics are discovered and then run tests on the newly-discovered laws of physics to see if a preferred reference frame emerges. I am guessing there is not much else we can do to answer this question until then.

1 minute ago, swansont said:

We can always measure a speed with respect to another frame. What we can't do is tell which one is at rest. Are we moving and that frame is at rest, or is it the other way around.

A preferred frame is one where the physics tells you that you are definitely at rest. We can do this with accelerations — you can tell if you are accelerating. But not with velocity. 

I already fully understand what you have said here and that that it applies if there is no external indicator telling you whether or not you are at rest. However, it seems to me (perhaps wrongly) that the CMB can be used as an external indicator because I am theorising that you are absolutely at rest if you can't detect a cosmic dipole. Can you explain why I might be wrong?

21 minutes ago, swansont said:

Cosmic dipole? Do you mean the CMB dipole, which is caused by our motion WRT the CMB, and vanishes when the motion is removed? And does not, then, represent a preferred frame (in the sense provided by relativity)?

The fact that we can be either moving or stationary relative to something as fundamental as the CMB seems to suggest to me that a preferred frame does exist. Is there something I am not understanding here? If yes, I would be very grateful if you could explain it to me.

45 minutes ago, Strange said:

Beliefs are of no value. How would one test for a preferred frame? And why have all such tests failed?

I think that provided that you humbly accept that your beliefs and opinions might be wrong, there is no harm in having them. In various documentaries, I often see eminent scientists expressing their beliefs and disagreements with each other. It is all part of a healthy scientific debate. Science dies if this stops.

I might be wrong but I think that the cosmic dipole might be evidence for a preferred frame.

7 minutes ago, Eise said:

I know. The idea is derived from the fact that, because simultaneity is relative to the movement of the observer, so automatically past, present and future must be too. (Of course only when events do not lie in each others light cones.) But this does not follow:

Changes are differences when we follow the timeline. But timelines do not disappear suddenly when we look at the universe as a 'block universe'.

And as you see, it is notoriously difficult to talk about such things and not using time-like concepts again: in your sentence the word 'pass'.

Hi Eise

In my reply to Swasont earlier in this thread, I mentioned that for the sake of impartiality, I have actually been doing a certain amount of devil's advocacy in this thread. My previous reply to you was such an example so I actually agree with what you are saying. On various science documentaries, I have seen some very eminent scientists speaking about the SpaceTime Block as being a static object when viewed from a perspective outside of time. I suppose therefore the question is, does such a perspective really exist?

21 minutes ago, Eise said:

The idea is derived from the fact that, because simultaneity is relative to the movement of the observer, so automatically past, present and future must be too.

Hi Eise

Since my reply to you a few minuets ago, I have looked more closely at this particular part of your reply and have dome some more thinking about it. What you say here assumes that there does not exist a "special" or "preferred" reference frame. I know this is somewhat controversial but I personally believe that a "special" or "preferred" reference frame does actually exist. I might be wrong though.

5 minutes ago, studiot said:

 

I think the question to be ill defined.

What do you mean by change?

 

Consider the following situation.

A man possesses 7 white shirts, 7 black ties, seven pairs of black trousers, seven pairs of black socks and seven pairs of black shoes.

Every day he washes and changes his set of clothes but he always looks the same.

 

Is there any change of appearance?

Hi Studiot

Thank you very much for your reply.

Very interesting question.

I think I define change to be any alteration whatsoever (however small) of the relationship between at least two subatomic particles.

In your example, the man and his clothing are all large macroscopic objects consisting of gazillions of subatomic particles. So each shirt or each tie may look the same but they each consist of a unique pattern of subatomic particles. Also, the processes of washing and changing them entails a huge amount of change.