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Comment Re:No programmers' typeface (Score 1) 175

The international dialing code for Kazakhstan from the UK would be 00 7 (I've just looked it up). I've never heard anyone quote a Kazakhstan telephone number to call from the UK but I would expect them to say oh oh seven, not double oh seven. Apart from anything else, if you did try to tell someone a Kazakhstan telephone number and started double oh seven I'd expect them to not hear the rest of the number while they were laughing.

Comment Re:No programmers' typeface (Score 1) 175

Saying oh for zero is common in (British) English.

Dialing code for London:
020 - Oh two oh.

Start of a telephone number:
700 - seven double oh.

International dialing code for the US:
00 1 - oh oh one. (Don't know why we don't say double oh but I've never heard it said that way.)

Bus number:
205 - two oh five

In normal spoken or written English you can usually determine whether it's a zero or a letter-o from the context and where you can't it rarely matters.

Comment Re:a crypto-token already in your wallet (Score 1) 210

In the UK for while we started getting little keypads - completely stand alone that you plugged your card into, entered the PIN, entered some other details (e.g. amount of transaction if necessary) and then got an 8 digit code back to use as a passcode.

Completely OS/browser agnostic.

Unfortunately, it never really took off. I think people just didn't find it convenient enough to have the keypad. Of course, had it taken off then people would have had multiple keypads and left one at work etc so they wouldn't have to carry them around. Also, of course, it was completely interchangeable between cards, so the business that paid to produce and distribute would have ended up subsidizing other businesses anti-fraud department.

I don't know whether something similar is possible now using a phone and near field communication with the card. But even if it is, I cannot see it taking off. The businesses that could do this are too concerned with locking customers into their app rather than getting together to solve a common problem in a common way.

Similar has happened with "smart meters" for electricity. We're in the middle of a national rollout (costing goodness knows how much) but change supplier and your smart meter will revert to a dumb meter.

Comment Re:I Think this article might be a bit misleading. (Score 1) 189

Sorry, I'm hopeless at explaining hence why I could never teach.

There aren't two identical "messages" in quantum teleportation. That would violate the no-cloning theorem. Instead there's one message that originally exists at point A and later exists at point B instead.

But - and this is the bit where it involves QM weirdness - there is no way to "read" a complete quantum state and record it classically. Think of it as a two bit word in a computer where every time you read one bit the reading circuit randomly disturbs the other bit.

QM teleportation lets us move that word from one place to another without changing either bit (but note that the original word (letter) is destroyed in the process.)

Comment Re:I Think this article might be a bit misleading. (Score 1) 189

I don't know what else you saw but basically the entanglement leaves the target (teleportation) end in a superposition of four states, only one of which is the one you want the others are complementary states.

The sender makes a measurement at their end to determine which one of the four states is the correct one and then transmits it to the receiver. The receiver can then isolate the correct state from the others that would otherwise cancel out all knowledge of the original state.

Comment Re:Can Anyone Explain This To Me? (Score 2) 189

Oh well. I tried to write a comment with a diagram but hit submit instead of preview :-(

Consider four directions on a plane. x axis (we'll call that |+>), y axis (we'll call that |->) y=-x (we'll call that |0>) and y=x (we'll call that |1>)

Modulo some constant factors, I hope it's obvious that you can build up some of those vectors from others:

|1> = |+> + |->
|-> = |0> + |1>

These are the directions of a plane polarized photon.

We setup some photons that are polarized in the |1> direction and then pass them through a polarization filter.

If the filter points along the |1> direction then all of them pass. If the filter passes along the |0> direction then none of them pass.

Now we put the filter along the |-> direction. What happens.

|1> = s|+> + s|-> (s is 1/sqrt(2) - which can be deduced from standard trig - the lines must be the same length)

When we measure along the |-> direction the s|-> part will pass the filter but the s|+> part wont.

But an individual photon can't get dimmer therefore it must either pass or not. Half the photons do pass and half don't (and it's random whether any one photon gets through the detector)

The ones that do get through are now in state |-> which is also |0>+|1> (again with factors of sqrt 2)

If we now measure along the |1> direction again we now lose half the photons again (due to that |0> component)

Quantum teleportation involves taking a photon in state a|0> + b|1> (for unknown values of a and b) and taking very careful measurements that don't destroy a and b but instead transfer them to another photon without us actually knowing what they are.

Comment Re:Coincidence circuit again, i.e. filtering (Score 3, Informative) 189

You got the first paragraph right. But then got sidetracked by tennis balls.

There are *two* complementary quantum states that you can measure. Measuring one destroys all knowledge of the other.

There is no classical system that behaves like this, therefore any analogy that doesn't invoke some magic artificial property of a classical object won't represent what happens in QM.

In your example you need tennis balls that randomly change colour when you measure their spin and can magically reverse spin when you look what colour they are.

Comment Re:Confused (Score 1) 189

Quantum teleportation requires the use of a classical channel. The entangled particles can be exchanged in advance (provided they can be stored without breaking the entanglement which is difficult in practice but trivial in theory)

The classical data can only be transferred at the time the teleportation is done - hence that limits the speed of the teleportation to the speed of light.

Comment Re:I Think this article might be a bit misleading. (Score 5, Informative) 189

It's effectively** equivalent to having two identical letters containing a random message

No. you're describing entanglement.

Teleportation is subtly different.

Teleportation consists of transferring the quantum state of one particle to another particle via the use of entangled particles (and a classical channel)

The beauty of this is that the entangled state can be set up in advance. You then give me a particle that you might or might not know something about its quantum state (but importantly, I do not know what you know about it so cannot measure that quantum state in advance). I can transfer the state of that particle to another particle that Bob has via some entangled particles we exchanged earlier *plus* some standard classical information that goes over classical channels (it's this classical information that limits the teleportation to the speed of light)

The particle that Bob ends up with is in an identical state the the one you gave me (and which I still have).

N.B. This is quantum teleportation, not quantum cloning which is not possible. The act of getting the quantum state to Bob affects my particle in a way that means I cannot also extract any information from it about the original state of your particle.

Comment Re:Coincidence circuit again, i.e. filtering (Score 2) 189

I think you misunderstand.

The experiments that are discarded are where the two end points don't measure the same quantum variable.

For photons, for example, you can measure whether linear polarization is up-down/left-right or diagonal-left-up diagonal-right-down/diagonal-right-up diagonal-left down.

If both ends measure the up-down/left-right state then one will get up-down, one left-right. If both measure the diagonal polarization then again they will get complementary results. But if one measures up-down and the other measures diagonal then we cannot tell anything useful any more than trying to compare two sweets where one person says what shape it is and the other says what flavour it is so those results get discarded.

There is additional statistical analysis - due to the fact that these experiments are done on single photons and sometimes detectors fire when there is no photon and sometimes they don't fire when there is so we cannot expect 100% correlation - but that's nothing to do with discarding some of the results.

Comment Re:Nobody knows yet (Score 1) 165

Basically, they have promised to veto any Article 50 agreement that doesn't continue to allow free travel (with ID) for their citizens to the UK, as is currently the case. Any Article 50 agreement requires a unanamous vote in favour - all 27 remaining countries

This isn't quite correct. An article 50 agreement requires, iirc at least 50% of member states representing at least 66% of the EU population.

However, I think disconnecting access to the free market from freedom of travel does require unanimity. That's an independent rule of the EU IIUC unrelated to article 50.

What isn't obvious at this point is whether the UK can negotiate some (acceptable) restrictions in trade in return for some (acceptable) restrictions in movement.

It may well end up with WTO rules due to the 2 year negotiating period expiring. Britain will then, of course, lose it's passporting rights to the financial markets. Whether the finance industry will have relocated in time is debatable - it probably depends on how early on failure of negotiations becomes apparent.

Comment Re:points of interest (Score 1) 532

How does the energy efficiency of this drive compare to a normal rocket?

Utter crap. But what it would give (assuming it works) is freedom from having to carry reaction mass.

But if it works, then it's going to open a whole new world in physics that hasn't been considered up until now - and it's likely to be obsolete within a few years once a theory that explains it comes to light.

(I'm betting on measurement error but hoping for something much more exciting)

Could this allow interstellar travel, by humans, within a normal human lifespan?

In theory yes - provided you can carry enough energy in a small enough mass. But interstellar travel precludes the use of solar energy so it's most likely to be useful in manoeuvring spacecraft around the inner solar system.

What kind of reletavistic effects happen at high speed? I would assume thrust would drop as you approach C.


Comment Re:I hate Apple, but no (Score 1) 564

However, you can't claim you're owed past money when Apple wasn't hiding anything.

I don't know about EU law but in the UK this is, indeed the case.

Tax avoidance schemes have to be registered with HMRC. If they are deemed to be invalid then you have to pay the tax that was due.

If you decide to fight it through the courts and the courts find in HMRCs favour then your tax liability is a multiple (greater than or equal to 1) of the tax that you tried to avoid. (plus any legal fees)

There was a very recent case along exactly these lines:

And another that looks like it will go HMRCs way.

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