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lightspeed

January 1st, 2015 Comments off

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Aon Tower, as seen from Lurie Garden in Millennium Park

Millennium Park in Chicago is a remarkable place. Skyscrapers shoulder together and soar up steeply to the north and to the west. The vertiginous effect of their cliff faces is reminiscent of Yosemite Valley.

Lurie Garden is at the center of the park, and is given over largely to native plants that carpeted the Illinois landscape in the interval between the retreat of the glaciers and the advance of the corn fields. In the silence of a photograph with a narrow field of view, it is as if the city never existed.

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Lurie Garden

Restore the sound, and the the buzz and hum of insects are superimposed on the wash of urban noise. A swarm of bees, algorithmic in their efficiency, and attuned to the flowers’ black light glow, collect the nectar. 55% sucrose, 24% glucose and 21% fructose.

When viewed in microwaves and millimeter waves, say from 1 to 100 GHz, the Millennium Park scene displays a similarly jarring juxtaposition. The sky glows with the ancient three degree background radiation — the cosmic static of the Big Bang explosion — subtly brightest in the direction of the Virgo Supercluster. All around, the buildings, the roads and the sidewalks are lit up with manically pulsating wireless transmitters: routers, cell phones, myriad sensors. In highly focused 6 GHz and 11 GHz beams, billions of dollars in coded securities orders streak above the urban canyons on line-of-sight paths linking the data centers of Chicago, Aurora, and suburban New Jersey. The fastest path of all runs through the top of the monolithic Aon Tower, where the signal is amplified and launched onward across the Lake and far into Michigan.

The microwave beams are a new development. In mid-2010, price movements at the Chicago Mercantile Exchange generated reactions in New Jersey nine milliseconds later. The signals traveled on fiber optic cables that meandered along railroad rights-of-way.

stockResponse2010

Now, the messages arrive within a few microseconds of the time it would take light to travel in vacuum, galvanizing the swarm of algorithms that are continually jostling and buzzing in the vicinity of the match.

stockResponse2013

Categories: worlds Tags:

optical data transmissions

November 28th, 2014 2 comments

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The amount of information that can be carried on a laser diode-driven fiber optic cable is staggering. The current state-of-the-art is of order a petabit per second over 50 km, with a direct power consumption of order 100 milliwatts, as described in this press release from NTT, and in primers on optical communication.

When data is transmitted via optical fiber, no signal leaks into space at all (other than a trivial quantity of waste heat). From the standpoint of eavesdropping civilizations, Earth is going dark, presenting a fashionable and much-remarked potential solution to the Fermi Paradox.

To order of magnitude, fiber optic cables currently employ 10^-16 ergs to transmit one bit of information over a distance of one centimeter. It’s interesting to compare this with the energy throughput and transmission efficiency of the first recorded description of an optical information transmission network.

In The Information — A History¬† A Theory A Flood, James Gleick draws attention to a passage that appears in¬†Aeschylus’ Agammemon describing how a chain of eight signal bonfires transmitted the news of Trojan defeat over the course of a single night to Clytemnestra, scheming, four hundred miles away in Sparta.

Aeschylus’ full passage is worth tracking down and is thrilling to read; a satisfyingly direct antecedent to NTT’s press release describing their record-setting petabyte per second optical data transmissions.

LEADER:

Yet who so swift could speed the message here?

CLYTEMNESTRA:

From Ida’s top Hephaestus, lord of fire,
Sent forth his sign; and on, and ever on,
Beacon to beacon sped the courier-flame.
From Ida to the crag, that Hermes loves,
Of Lemnos; thence unto the steep sublime
Of Athos, throne of Zeus, the broad blaze flared.
Thence, raised aloft to shoot across the sea,
The moving light, rejoicing in its strength,
Sped from the pyre of pine, and urged its way,
In golden glory, like some strange new sun,
Onward, and reached Macistus’ watching heights.
There, with no dull delay nor heedless sleep,
The watcher sped the tidings on in turn,
Until the guard upon Messapius’ peak
Saw the far flame gleam on Euripus’ tide,
And from the high-piled heap of withered furze
Lit the new sign and bade the message on.
Then the strong light, far-flown and yet undimmed,
Shot thro’ the sky above Asopus’ plain,
Bright as the moon, and on Cithaeron’s crag
Aroused another watch of flying fire.
And there the sentinels no whit disowned,
But sent redoubled on, the hest of flame
Swift shot the light, above Gorgopis’ bay,
To Aegiplanctus’ mount, and bade the peak
Fail not the onward ordinance of fire.
And like a long beard streaming in the wind,
Full-fed with fuel, roared and rose the blaze,
And onward flaring, gleamed above the cape,
Beneath which shimmers the Saronic bay,
And thence leapt light unto Arachne’s peak,
The mountain watch that looks upon our town.
Thence to th’ Atreides’ roof-in lineage fair,
A bright posterity of Ida’s fire.
So sped from stage to stage, fulfilled in turn,
Flame after flame, along the course ordained,
And lo! the last to speed upon its way
Sights the end first, and glows unto the goal.
And Troy is ta’en, and by this sign my lord
Tells me the tale, and ye have learned my word.

Given that the message was one bit, the signal coding was at the Shannon Limit. The route can be correlated with current-day geographic features,

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and then traced out in Google Earth:

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The bonfire on Mt. Ida that signaled the end of the Trojan War probably consumed about a cord (3.62 cubic meters) of wood and emitted about 5×10^12 ergs/sec over a span of an hour, for a transmission efficiency of order 10^9 ergs per centimeter per bit. A mere three thousand years has brought twenty five orders of magnitude of improvement.

With the take-away being that the quality of the message is likely superior in importance to the quantity.

Categories: worlds Tags:

1215095

January 25th, 2014 2 comments

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Above: A Google Data Center Image source.

A few weeks ago, there was an interesting article in the New York Times.

On the flat lava plain of Reykjanesbaer, Iceland, near the Arctic Circle, you can find the mines of Bitcoin.

To get there, you pass through a fortified gate and enter a featureless yellow building. After checking in with a guard behind bulletproof glass, you face four more security checkpoints, including a so-called man trap that allows passage only after the door behind you has shut. This brings you to the center of the operation, a fluorescent-lit room with more than 100 whirring silver computers, each in a locked cabinet and each cooled by blasts of Arctic air shot up from vents in the floor.

The large-scale Bitcoin mining operation described in the article gravitated to Iceland in part because of the cheap hydroelectric power (along with natural air conditioning, the exotic-location marketing style points, and a favorable regulatory environment). Bitcoin mining is part of a emergent global trend in which the physical features and the resource distribution of the planet are being altered by infrastructure devoted to the computation that occurs in data centers. As an example, here is a map showing new 6, 11, and 18 GHz site-based FCC microwave-link license applications during the past three years.

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The Western terminus of the triangle is a mysterious building (read data center) just a mile or so south of Fermilab (for more information see this soon-to-be-published paper of mine co-authored with Anthony Aguirre and Joe Grundfest).

Data Centers are currently responsible for about 2% of the world’s 20,000 TWH yearly electricity consumption, which amounts to roughly 1.4×10^24 ergs per year. If we use the Tianhe 2 computer (currently top of the list at top500.org, with a computational throughput of 33.8 petaflops, and a power usage of 17,808 kW) as a forward-looking benchmark, and if we assume that a floating-point operation consists of ~100 bit operations, the data centers of the world are carrying out 3×10^29 bit operations per year (70 moles per second).

I’ll define a new cgs unit:

1 oklo = 1 artificial bit operation per gram of system mass per second

Earth, as a result of its data centers, is currently generating somewhat more than a microoklo, and if we take into account all of the personal devices and computers, the planetary figure is likely at least several times that.

I think it’s likely that for a given system, astronomically observable consequences might begin to manifest themselves at ~1 oklo. The solar system as a whole is currently running at ~10 picooklos. From Alpha Centauri, the Sun is currently just the nearest G2V star, but if one strains one’s radio ears, one can almost hear the microwave transmissions.

Landauer’s principle posits the minimum possible energy, E=kTln2, required to carry out a bit operation. The Tianha-2 computer is a factor of a billion less efficient than the Landauer limit, and so it’s clear that the current energy efficiency of data centers can be improved. Nevertheless, even if running near the Landauer limit, the amount of computation done on Earth would need to increase several hundredfold for the Solar System to run at one oklo.

So where to look? Three ideas come to mind in increasingly far-out order.

(1) Dyson spheres are the perennial favorite. Several years ago, when the WISE data came out, I worked with two high-school students from UCSC’s Summer Internship Program to search the then newly-released WISE database for room-temperature blackbodies. To our surprise, it turns out that the galactic disk is teeming with objects that answer to this description:

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(Some further work revealed that they are heavily dust-obscured AGB stars.)

(2) Wait long enough, and your data center will suffer an impact by a comet or an asteroid, and computational hardware debris will begin to diffuse through the galaxy. In the event that this happened regularly, then it might be possible to find some interesting microscopic things in carbonaceous chondrites.

(3) The T in Landauer’s principle suggests that cold locations are better suited for large-scale computation. Given that here on Earth a lot of cycles are devoted to financial computation, it might also be relevant to note that you get a higher rate of return on your money if your bank is in flat space time and you are living in a region of highly curved spacetime.

Categories: worlds Tags: ,