OT: This Swift thing

[Steven D'Aprano]

I'm not sure where Chris' message comes from, I can't see the original,
so I'm guessing the context.

Air cooled cars don't just cool the engine when they are travelling at
100kmh. Some air-cooled engines used a fan to blow extra air over the
cooling fins, but many did not. Normal air flow is sufficient to keep
them in a safe operating temperature, the hot engine warms the air, which
flows away and is replaced by cooler air.

It's possible to design CPUs to work the same way. My wife is using a PC
right now with a 1.66GHz Atom CPU and no CPU fan. Even though the power
supply fan died, the machine is still running perfectly, with two laptop
HDDs, and no overheating. 1.66GHz is plenty fast enough for web browsing,
word processing, email, etc.

Go back 30 years, and I don't think that the average PC needed a CPU fan.
Possibly not even a case fan. Just the normal air flow over a small heat
sink was enough. And of course, your mobile phone has no room for a heat
sink, unless it's tiny, and no fan. And people expect it to keep working
even when shoved in their pocket.

If the car were *always* moving at 100km/h, it probably wouldn't need a
fan.

In practice, all cars do have fans (even the ones that aren't
air-cooled), for the occasions when they're not moving that fast.

That may be true of water-cooled engines *now*, but it's not a law of
engineering. Many air-cooled engines do not (did not) require a fan, or
only needed the extra cooling when stuck idling for long periods in hot
weather. E.g. Beetles didn't use a fan. (A great idea for Germany, not so
much for hot and dusty Southern California, as my wife can tell you.)

(BTW, so-called water-cooled engines are really air-cooled too, just not
by air flowing directly over the engine block. (Although marine engines
may be an exception.))

Yes, technically water-cooled engines are cooled by air too. The engine
heats a coolant (despite the name, usually not water these days) which
then heats the air.

 

[Roy Smith]

Yes, technically water-cooled engines are cooled by air too. The engine
heats a coolant (despite the name, usually not water these days) which
then heats the air.

Not water??? I'm not aware of any water-cooled engines which use
anything other than water. Well, OK, it's really a solution of ethylene
or propylene glycol in water, but the water is what does most of the
heat transfer. The glycol is just there to provide freezing point
depression and boiling point elevation.

 

[Steven D'Aprano]

With a car, the engine converts some of its energy to kinetic energy,
which is subsequently dissipated as heat, so it makes sense to talk
about the ratio of kinetic energy produced to energy wasted directly as
heat.

But when you flip a bit, there's no intermediate form of energy -- the
bit changes state, and heat is produced. So all of the heat is waste
heat.

Not the point. There's a minimum amount of energy required to flip a bit.
Everything beyond that is, in a sense, just wasted. You mentioned this
yourself in your previous post. It's a *really* tiny amount of energy:
about 17 meV at room temperature. That's 17 milli electron-volt, or
2.7×10^-21 joules. In comparison, Intel CMOS transistors have a gate
charging energy of about 62500 eV (1×10^-14 J), around 3.7 million times
greater.

Broadly speaking, if the fundamental thermodynamic minimum amount of
energy needed to flip a bit takes the equivalent of a single grain of
white rice, then our current computing technology uses the equivalent of
175 Big Macs.

(There are approximately 50 grains of rice in a gram, and a gram of rice
is about 1.3 Calories. A Big Mac is about 550 Calories. You do the maths.)

 

[Rustom Mody]

With a car, the engine converts some of its energy to
kinetic energy, which is subsequently dissipated as heat,
so it makes sense to talk about the ratio of kinetic
energy produced to energy wasted directly as heat.

But when you flip a bit, there's no intermediate form
of energy -- the bit changes state, and heat is produced.
So all of the heat is waste heat.

Actually the car-drive and the bit-flip are much more identical than
different. Its just that the time-scales are minutes/hours in one
case and nanoseconds or less in the other so our powers of
visualization are a bit taxed.

In more detail:

One drives a car from A to B for an hour (assume no change in
height above sea level so no potential difference).
All the energy that was there as petrol has been dissipated as heat.

A bit flips from zero to one. Pictorially
(this needs to be fixed-pitch font!):

+-------------
|
|
|
-----------+

However in reality that 'square' wave is always actually sloped


+----------
/
/
/
-----------+

Now for say CMOS technology, one may assume no currents in both zero
and one states (thats the C in CMOS). However when its neither zero
nor one (the sloping part) there will be current and therefore heat.

So just as the car burns energy in going from A to B, the flipflop
burns it in going from 0 to 1

Not the point. There's a minimum amount of energy required to flip a bit.
Everything beyond that is, in a sense, just wasted. You mentioned this
yourself in your previous post. It's a *really* tiny amount of energy:
about 17 meV at room temperature. That's 17 milli electron-volt, or
2.7×10^-21 joules. In comparison, Intel CMOS transistors have a gate
charging energy of about 62500 eV (1×10^-14 J), around 3.7 million times
greater.

Broadly speaking, if the fundamental thermodynamic minimum amount of
energy needed to flip a bit takes the equivalent of a single grain of
white rice, then our current computing technology uses the equivalent of
175 Big Macs.

Well thats in the same realm as saying that by E=mc² a one gram stone can yield
21 billion calories energy.

[Ive forgotten how the units stack up, so as usual relyin on google
instead of first principles:

http://en.wikipedia.org/wiki/Mass–energy_equivalence#Practical_examples

]

ie. from a a pragmatic/engineering pov we know as much how to use
Einstein's energy-mass-equivalence to generate energy as we know how
to use Landauer's principle to optimally flip bits.

 

[Dennis Lee Bieber]

Not water??? I'm not aware of any water-cooled engines which use
anything other than water. Well, OK, it's really a solution of ethylene
or propylene glycol in water, but the water is what does most of the
heat transfer. The glycol is just there to provide freezing point
depression and boiling point elevation.

The point was that said coolant is, itself, cooled via an air/water
heat exchanger (the radiator -- which in most cars proceeds to then pass
the now-heated air back over the engine <G>)

 

[Steven D'Aprano]

Not water??? I'm not aware of any water-cooled engines which use
anything other than water. Well, OK, it's really a solution of ethylene
or propylene glycol in water, but the water is what does most of the
heat transfer. The glycol is just there to provide freezing point
depression and boiling point elevation.

Would you consider it fair to say that, say, vinegar is "not water"?
Depending on the type of vinegar, it is typically around 5-10% acetic
acid, and the rest water. Spirit vinegar can be as much as 20% acetic
acid, which still leaves 80% water.

How about brandy, which is typically 35%-60% alcohol, with most of the
rest being water? Or household bleach, which is typically a 3-6% solution
of sodium hypochlorite? Or milk (85-90% water)? I think it is fair to
describe those as "not water". You shouldn't try to put out a fire by
pouring a bottle of brandy on it.

Automotive cooling fluid in modern sealed radiators is typically a
mixture of 50% anti-freeze and 50% water.

Back in the day, car radiators were *literally* water-cooled in the sense
that the radiator was filled with 100% water. You filled it from the tap
with drinking water. In an emergency, say broken down in the desert, you
could drink the stuff from the radiator to survive. If you tried that
with many modern cars, you would die a horrible death.

 

[Steven D'Aprano]

Not the point. There's a minimum amount of energy required to flip a
bit. Everything beyond that is, in a sense, just wasted. You mentioned
this yourself in your previous post. It's a *really* tiny amount of
energy: about 17 meV at room temperature. That's 17 milli
electron-volt, or 2.7×10^-21 joules. In comparison, Intel CMOS
transistors have a gate charging energy of about 62500 eV (1×10^-14 J),
around 3.7 million times greater.

Broadly speaking, if the fundamental thermodynamic minimum amount of
energy needed to flip a bit takes the equivalent of a single grain of
white rice, then our current computing technology uses the equivalent
of 175 Big Macs.

Well thats in the same realm as saying that by E=mc² a one gram stone
can yield 21 billion calories energy. [...]
ie. from a a pragmatic/engineering pov we know as much how to use
Einstein's energy-mass-equivalence to generate energy as we know how to
use Landauer's principle to optimally flip bits.

You know, I think that the people of Hiroshima and Nagasaki and Chernobyl
and Fukushima (to mention only a few places) might disagree.

We know *much more* about generating energy from E = mc^2 than we know
about optimally flipping bits: our nuclear reactions convert something of
the order of 0.1% of their fuel to energy, that is, to get a certain
yield, we "merely" have to supply about a thousand times more fuel than
we theoretically needed. That's about a thousand times better than the
efficiency of current bit-flipping technology.

We build great big clanking mechanical devices out of lumps of steel that
reach 25% - 50% of the theoretical maximum efficiency:

https://en.wikipedia.org/wiki/Thermal_efficiency

while our computational technology is something of the order of 0.00001%
efficient. I'm just pointing out that our computational technology uses
over a million times more energy than the theoretical minimum, and
therefore there is a lot of room for efficiency gains without sacrificing
computer power. I never imagined that such viewpoint would turn out to be
so controversial.

 

[Gregory Ewing]

Automotive cooling fluid in modern sealed radiators is typically a
mixture of 50% anti-freeze and 50% water.

Sometimes it's even more than 50%, at which point
you really have an antifreeze-cooled engine.

 

[Chris Angelico]

I'm just pointing out that our computational technology uses
over a million times more energy than the theoretical minimum, and
therefore there is a lot of room for efficiency gains without sacrificing
computer power. I never imagined that such viewpoint would turn out to be
so controversial.

The way I understand it, you're citing an extremely theoretical
minimum, in the same way that one can point out that we're a long way
from maximum entropy in a flash memory chip, so it ought to be
possible to pack a lot more data onto a USB stick. The laws of physics
tend to put boundaries that are ridiculously far from where we
actually work - I think most roads have speed limits that run a fairly
long way short of c.

ChrisA

 

[Gene Heskett]

Sometimes it's even more than 50%, at which point
you really have an antifreeze-cooled engine.

There have been cases where that 50% may have been exceeded actually
driving on the streets.

At least 3 decades back, not too long before caddy came out with the
northstar engine, which was rigged to get you home at a reasonable speed
even if the radiator had been holed & the coolant lost. They used a wee
bit of the knowledge gained from keeping Smokey Yunick is experimenting
cash. He had an old VW Rabbit that was both a parts car, and the test
bed. Two cylinder motor, I suspect built on a Harley 78cid crankcase, no
radiator, no air cooling. Ceramic cylinders and pistons, it ran at a
quite high internal temperature because the cylinders were insulated from
losing heat by fiberglass blankets. It displaced 78 cid, made about 150
HP, and got well over 120 mpg running around in Daytona Beach. The one
magazine article said it hadn't lost a stoplight grand prix ever but
Smokey stopped that by making whoever was driving it, 100% responsible for
any tickets it collected.

It would have been gawdawful expensive to put it into production since
those 2 cylinders & pistons cost more than the complete V8 Northstar
engine.

I thought it was one radically cool idea at the time. And I am amazed
that something like it has not invaded the automotive world what with all
the emphasis on both high mileage & decent horsepower caused by the high
petro prices. Today I'd imagine a new cat converter might need to be
built because at those temps and compression ratio's, I can see a hugely
illegal amount of the various nitrogen oxides the EPA wouldn't tolerate.

Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

 

[Steven D'Aprano]

The way I understand it, you're citing an extremely theoretical minimum,
in the same way that one can point out that we're a long way from
maximum entropy in a flash memory chip, so it ought to be possible to
pack a lot more data onto a USB stick.

Um, yes?

Hands up anyone who thinks that today's generation of USB sticks will be
the highest capacity ever, that all progress in packing more memory into
a thumb drive (or the same memory into a smaller drive) will cease
effective immediately?

Anyone?

The laws of physics tend to put
boundaries that are ridiculously far from where we actually work - I
think most roads have speed limits that run a fairly long way short of
c.

"186,000 miles per second: not just a good idea, it's the law"


There's no *law of physics* that says cars can only travel at the speeds
they do. Compare how fast a typical racing car goes with the typical
60kph speed limit in suburban Melbourne. Now compare how fast the
Hennessey Venom GT goes to that speed limit.

http://www.autosaur.com/fastest-car-in-the-world/?PageSpeed=noscript


Speed limits for human-piloted ground-based transport ("cars") are more
based on social and biological factors than engineering ones. Similarly,
there are biological factors that force keyboards to be a minimum size.
We probably could build a keyboard where the keys were 0.1mm square, but
what would be the point? Who could use it? Those social and biological
factors don't apply to computing efficiency, so it's only *engineering*
factors that prevent us from being able to run your server off a watch
battery, not the laws of physics.

It is my contention that, had Intel and AMD spent the last few decades
optimizing for power consumption rather than speed, we probably could run
a server off, well, perhaps not a watch battery, but surely a factor of
100 improvement in efficiency isn't unreasonable given that we're just
moving a picogram of electrons around?

 

[Gregory Ewing]

It is my contention that, had Intel and AMD spent the last few decades
optimizing for power consumption rather than speed, we probably could run
a server off, well, perhaps not a watch battery,

Current draw of CMOS circuitry is pretty much zero when
nothing is changing, so if you didn't care how slow it ran,
you probably could run a server off a watch battery today.
Users wouldn't like waiting a week for their web pages to
load, though...

 

[Rustom Mody]

I am bewildered by this argument...

[Heck Ive recently learnt that using ellipses is an easy way to
produce literature... So there...]

It is my contention that, had Intel and AMD spent the last few decades
optimizing for power consumption rather than speed, we probably could run
a server off, well, perhaps not a watch battery, but surely a factor of
100 improvement in efficiency isn't unreasonable given that we're just
moving a picogram of electrons around?

This is fine and right.
I personally would pay more if my PCs/laptops etc were quieter/efficient-er.
So we agree... upto here!

Um, yes?

Hands up anyone who thinks that today's generation of USB sticks will be
the highest capacity ever, that all progress in packing more memory into
a thumb drive (or the same memory into a smaller drive) will cease
effective immediately?

"186,000 miles per second: not just a good idea, it's the law"

There's no *law of physics* that says cars can only travel at the speeds
they do. Compare how fast a typical racing car goes with the typical
60kph speed limit in suburban Melbourne. Now compare how fast the
Hennessey Venom GT goes to that speed limit.

http://www.autosaur.com/fastest-car-in-the-world/?PageSpeed=noscript

Now you (or I) are getting completely confused.

If you are saying that the Hennessey Venom (HV) is better than some
standard vanilla Ford/Toyota (FT) based on the above, thats ok.

In equations:
maxspeed(HV) = 250 mph
maxspeed(FT) = 150 mph
so HV is better than FT.

Ok...

But from your earlier statements you seem to be saying its better
because:
250 mph is closer to 186,000 mps (= 670 million mph) than 150 mph

Factually this is a correct statement.

Pragmatically this is as nonsensical as comparing a mile and a
kilogram.

Speed limits for human-piloted ground-based transport ("cars") are more
based on social and biological factors than engineering ones. Similarly,
there are biological factors that force keyboards to be a minimum size.
We probably could build a keyboard where the keys were 0.1mm square, but
what would be the point? Who could use it? Those social and biological
factors don't apply to computing efficiency, so it's only *engineering*
factors that prevent us from being able to run your server off a watch
battery, not the laws of physics.

As best as I can see you are confused about the difference between
science and engineering.

Saying one car is better engineered than another on direct comparison
(150mph<250mph) is ok

Saying one car is better than another because of relation to physics
limits (c-150>c-250) is confusing science and engineering.

Likewise saying AMD and Intel should have done more due diligence to
their clients (and the planet) by considerging energy efficiency is right
and I (strongly) agree.

But compare their products' realized efficiency with theoretical limits like
Landauers is a type-wrong statement

 

[Steven D'Aprano]

Now you (or I) are getting completely confused.

If you are saying that the Hennessey Venom (HV) is better than some
standard vanilla Ford/Toyota (FT) based on the above, thats ok.

I'm not making any value judgements ("better" or "worse") about cars
based on their speed. I'm just pointing out that the speed limits on our
roads have very little to do with the speeds cars are capable of
reaching, and *nothing* to do with ultimate limits due to the laws of
physics.

Chris made the argument that *the laws of physics* put limits on what we
can attain, which is fair enough, but then made the poor example of speed
limits on roads falling short of the speed of light. Yes, speed limits on
roads fall considerably short of the speed of light, but not because of
laws of physics. The speed limit in my street is 50 kilometres per hour,
not because that limit is a law of physics, or because cars are incapable
of exceeding 50kph, but because the government where I live has decided
that 50kph is the maximum safe speed for a car to travel in my street,
rounded to the nearest multiple of 10kph.

In other words, Chris' example is a poor one to relate to the energy
efficiency of computing.

A more directly relevant example would have been the efficiency of heat
engines, where there is a fundamental physical limit of 100% efficiency.
Perhaps Chris didn't mention that one because our technology can build
heat engines with 60% efficiency, which is probably coming close to the
practical upper limit of attainable efficiency -- we might, by virtue of
clever engineering and exotic materials, reach 70% or 80% efficiency, but
probably not 99.9% efficiency. That's a good example.

Bringing it back to computing technology, the analogy is that our current
computing technology is like a heat engine with an efficiency of
0.000001%. Even an efficiency of 1% would be a marvelous improvement. In
this analogy, there's an ultimate limit of 100% imposed by physics
(Landauer's Law), and a practical limit of (let's say) 80%, but current
computing technology is so far from those limits that those limits might
as well not exist.

In equations:
maxspeed(HV) = 250 mph
maxspeed(FT) = 150 mph
so HV is better than FT.

"Better" is your word, not mine.

I don't actually care about fast cars, but if I did, and if I valued
speed above everything else (cost, safety, fuel efficiency, noise,
environmental impact, comfort, etc) then yes, I would say 250 mph is
"better" than 150 mph, because 250 mph is larger.

Ok...

But from your earlier statements you seem to be saying its better
because:
250 mph is closer to 186,000 mps (= 670 million mph) than 150 mph

Factually this is a correct statement.

And yet you're going to disagree with it, even though you agree it is
correct?

Pragmatically this is as nonsensical as comparing a mile and a kilogram.

This makes no sense at all.

Your two statements about speeds are logically and mathematically
equivalent. You cannot have one without the other.

Take three numbers, speeds in this case, s1, s2 and c, with c a strict
upper-bound. We can take:

s1 < s2 < c

without loss of generality. So in this case, we say that s2 is greater
than s1:

s2 > s1

Adding the constant c to both sides does not change the inequality:

c + s2 > c + s1

Subtracting s1 + s2 from each side:

c + s2 - (s1 + s2) > c + s1 - (s1 + s2)
c - s1 > c - s2

In other words, if 250mph is larger than 150mph (a fact, as you accept),
then it is equally a fact that 250mph is closer to the speed of light
than 150mph. You cannot possibly have one and not the other. So why do
you believe that the first form is acceptable, but the second form is
nonsense?

As best as I can see you are confused about the difference between
science and engineering.

Saying one car is better engineered than another on direct comparison
(150mph<250mph) is ok

Saying one car is better than another because of relation to physics
limits (c-150>c-250) is confusing science and engineering.

I do not understand what confusion you think you see here.

If we agree on the value judgement "greater top speeds are always
better", and the law of physics "c is the upper-limit to speeds", then
the following two statements are logically equivalent:

"Car HV is better than car FT because the HV has the greater top speed."

"Car HV is better than car FT because the HV's top speed is closer to c
than the FT's top speed."

These sorts of value judgments are independent of the *cause* of the
upper limit. Sticking to Chris' example of speed, if we agree that faster
travel is better than slower travel, then in the state of Victoria,
Australia, the ultimate upper-limit on (legal) speed is 110kph. If we
decide to value faster speeds, then the Hume Freeway with its 100kph
speed limit is better than my suburban back street with a 50kph speed
limit, even though the limit is a social restriction, not an engineering
limit or physics limit.

Likewise saying AMD and Intel should have done more due diligence to
their clients (and the planet) by considerging energy efficiency is
right and I (strongly) agree.

But compare their products' realized efficiency with theoretical limits
like Landauers is a type-wrong statement

If I were arguing that there are no engineering limits prohibiting CPUs
reaching Landauer's limit, then you could criticise me for that, but I'm
not making that argument.

I'm saying that, whatever the practical engineering limits turn out to
be, we're unlikely to be close to them, and therefore there are very
likely to be many and massive efficiency gains to be made in computing.

 

[Chris Angelico]

Chris made the argument that *the laws of physics* put limits on what we
can attain, which is fair enough, but then made the poor example of speed
limits on roads falling short of the speed of light. Yes, speed limits on
roads fall considerably short of the speed of light, but not because of
laws of physics. The speed limit in my street is 50 kilometres per hour,
not because that limit is a law of physics, or because cars are incapable
of exceeding 50kph, but because the government where I live has decided
that 50kph is the maximum safe speed for a car to travel in my street,
rounded to the nearest multiple of 10kph.

In other words, Chris' example is a poor one to relate to the energy
efficiency of computing.

The point isn't so much the legal or safe limit as that that's the
speed of most driving. That is to say: Around here, most cars will
travel at roughly 50 kph, which is a far cry from c. There are other
reasons than physics for choosing a speed.

Take three numbers, speeds in this case, s1, s2 and c, with c a strict
upper-bound. We can take:

s1 < s2 < c

without loss of generality. So in this case, we say that s2 is greater
than s1:

s2 > s1

Adding the constant c to both sides does not change the inequality:

c + s2 > c + s1

As long as we accept that this is purely in a mathematical sense.
Let's not get into the realm of actual speeds greater than c.

Subtracting s1 + s2 from each side:

c + s2 - (s1 + s2) > c + s1 - (s1 + s2)
c - s1 > c - s2

In other words, if 250mph is larger than 150mph (a fact, as you accept),
then it is equally a fact that 250mph is closer to the speed of light
than 150mph. You cannot possibly have one and not the other. So why do
you believe that the first form is acceptable, but the second form is
nonsense?

And at this point the calculation becomes safe again, and obvious
common sense. (Or alternatively, substitute Mach 1 for c; it's not a
hard limit, but there are good reasons for staying below it in
practical application - most airliners cruise a smidge below the speed
of sound for efficiency.)

If I were arguing that there are no engineering limits prohibiting CPUs
reaching Landauer's limit, then you could criticise me for that, but I'm
not making that argument.

I'm saying that, whatever the practical engineering limits turn out to
be, we're unlikely to be close to them, and therefore there are very
likely to be many and massive efficiency gains to be made in computing.

And this I totally agree with. The limits of physics are so incredibly
far from where we now are that we can utterly ignore them; the limits
we face are generally engineering (with the exception of stuff
designed for humans to use, eg minimum useful key size is defined by
fingers and not by what we can build).

ChrisA

 

[Gene Heskett]

On Fri, Jun 13, 2014 at 3:04 AM, Steven D'Aprano


And this I totally agree with. The limits of physics are so incredibly
far from where we now are that we can utterly ignore them; the limits
we face are generally engineering (with the exception of stuff
designed for humans to use, eg minimum useful key size is defined by
fingers and not by what we can build).

ChrisA

Thats a bit too blanketish a statement, we do see it in the real world.
Some of the electronics stuff we've been using for nearly 50 years
actually runs into the e=MC^2 effects, and it affects their performance in
pretty deleterious ways.

A broadcast power klystron, like a 4KM100LA, which is an electron beam
device that does its amplifying by modulating the velocity of an electron
beam which is being accelerated by nominally a 20,000 volt beam supply.
But because of the beam speed from that high a voltage brings in
relativity effects from e=MV^2 mass of the electrons in that beam, an
equal amount of energy applied to speed it up does not get the same
increase in velocity as that same energy applied to slow it down decreases
it. This has the net effect of making the transit time greater when under
high power drive conditions such as the sync pulses of the now out of
style NTSC signal. The net result is a group delay characteristic that is
uncorrectable when the baseband video is where you are trying to correct
it. In a few words, the shape of the sync signal is damaged. Badly.

Because most transmitters of that day used separate amplifiers for the
audio, and the receivers have used the 4.5 mhz difference signal to
recover the audio in the receiver for the last 63+ years, this "Incidental
Carrier Phase Modulation" noise is impressed into the detected audio. And
I am sure that there are many here that can recall back a decade that the
UHF stations in your area, all had a what was often called "chroma buzz"
in the audio that was only about 50 db down. Ear fatiguing at best.
Market share effecting too. And that translates directly into station
income minus signs.

It was fixable, but at an additional cost in efficiency of about -20%, but
consider what that 20% costs when a station using a 30kw rated
transmitter, actually pulls around 225 kwh from the powerline for every
hour it is on the air. Bean counters have heart attacks over such
figures.

Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS

 

[Rustom Mody]

As long as we accept that this is purely in a mathematical sense.
Let's not get into the realm of actual speeds greater than c.

You got a keen eye Chris -- didn't notice that!
And captures my point better than my long-winded attempts

 

[Steven D'Aprano]

On Fri, Jun 13, 2014 at 3:04 AM, Steven D'Aprano


As long as we accept that this is purely in a mathematical sense. Let's
not get into the realm of actual speeds greater than c.

Well, yes, it is in the mathematical sense, and it doesn't require any
actual physical thing to travel at faster than light speed. There is no
implication here that there is something travelling at (c + s1). It's
just a number.

But note that even in *real* (as opposed to science fiction, or
hypothetical) physics, you can have superluminal speeds. Both the phase
velocity and group velocity of a wave may exceed c; the closing velocity
of two objects approaching each other is limited to 2c. Distant galaxies
are receding from us at greater than c. There are other situations where
some measurable effect can travel faster than c, e.g. the superluminal
spotlight effect.

https://en.wikipedia.org/wiki/Faster-than-light

 

[Roy Smith]

Would you consider it fair to say that, say, vinegar is "not water"?
Depending on the type of vinegar, it is typically around 5-10% acetic
acid, and the rest water. Spirit vinegar can be as much as 20% acetic
acid, which still leaves 80% water.

In a car, the water is the important part (even if it's only a 50%
component). The primary job of the circulating coolant is to absorb
heat in one place and transport it to another place. That requires a
liquid with a high heat capacity, which is the water. The other stuff
is just there to help the water do its job (i.e. not freeze in the
winter, or boil over in the summer, and some anti-corrosive action
thrown into the mix).

When you said, "usually not water these days", that's a misleading
statement. Certainly, it's "not pure water", or even "just water". But
"not water" is a bit of a stretch.

With vinegar, the acetic acid is the important component. The water is
just there to dilute it to a useful working concentration and act as a
carrier. People are 90% water too, but I wouldn't call a person
"water". I would, however, as a first-order description, call the stuff
circulating through the cooling system in my car, "water".

Back in the day, car radiators were *literally* water-cooled in the sense
that the radiator was filled with 100% water. You filled it from the tap
with drinking water. In an emergency, say broken down in the desert, you
could drink the stuff from the radiator to survive. If you tried that
with many modern cars, you would die a horrible death.

But, I could do that right now, with my car (well, not the drinking
part) . In an emergency, I could fill my cooling system with pure
water, and it would work well enough to get me someplace not too far
away where I could get repairs done.

 

[Joshua Landau]

We know *much more* about generating energy from E = mc^2 than we know
about optimally flipping bits: our nuclear reactions convert something of
the order of 0.1% of their fuel to energy, that is, to get a certain
yield, we "merely" have to supply about a thousand times more fuel than
we theoretically needed. That's about a thousand times better than the
efficiency of current bit-flipping technology.

You're comparing a one-use device to a trillion-use device. I think
that's unfair.

Tell me when you find an atom splitter that works a trillion times.
Then tell me what it's efficiency is, because it's not nearly 0.1%.