Year: 2019

It Starts with a Paradox

Part 2 of World Build­ing for Sci­ence Fiction

Part 2—It starts with a paradox

 

Pho­to by Rakice­vic Nenad from Pex­els

 

 

The Fer­mi para­dox tries to answer: Where are they (the aliens)? It looks at how fast trav­el is across the galaxy.  It says by infer­ence the time to explore the 100 bil­lion solar sys­tems with­in the galaxy. The para­dox assumes that the first civ­i­liza­tion to emerge will find itself alone the cos­mos.  Because they find them­selves alone, the civ­i­liza­tion will try to fig­ure out the answer to the ques­tion: Where are they?  This arti­cle will show pos­si­ble for a civ­i­liza­tion to answer this question.

First off, we show that this ques­tion is not an unrea­son­able one.  Using the laws of nature, a civ­i­liza­tion real­izes that anoth­er sci­en­tif­i­cal­ly advanced civ­i­liza­tion could exist else­where.  They’ll real­ize their star is one of 100 bil­lion with­in the galaxy.  They’ll build tele­scopes and dis­cov­er oth­er plan­ets orbit­ing those stars.  They’ll con­tem­plate life on those plan­ets and won­der about intel­li­gent life.  The first civ­i­liza­tion to emerge will lis­ten to the cos­mos.  Fail­ing to detect anoth­er civ­i­liza­tion, they’ll ques­tion their assump­tions. Even­tu­al­ly, they will ask and answer it.

To car­ry out the answer, the civ­i­liza­tion needs to explore every solar sys­tem in the galaxy.  Can this be done?  One solu­tion is by col­o­niz­ing every solar sys­tem and prepar­ing to explore as they move out­ward.  The home world sends out col­o­niz­er space­ships to two near­by solar sys­tems. Each of the col­o­niz­ers estab­lish­es a colony to build col­o­niz­ers that explore two more solar sys­tems and so forth.  If it takes 10 years to make the jour­ney and two gen­er­a­tions before the next col­o­niz­ers are ready, then the dou­bling time for explored sys­tems is 50 years.  So, 50 years at a pace, the num­ber of ships explor­ing dou­bles, and fifty years at a time, the num­ber of sys­tems dou­bles.  If the galaxy were spher­i­cal with the civilization’s home world at the cen­ter of the sphere, the dou­bling pro­ceeds for 1850 years until they explore 100 bil­lion suns.  Since the galaxy is not spher­i­cal, we must account for the size and shape of the galaxy in the calculations.

The diam­e­ter of our galaxy’s disk is over 100,000 light years. The light cross­ing time is 100,000 years.  If a rea­son­able largest speed (using Einstein’s spe­cial rel­a­tiv­i­ty) is half the speed of light, then the space­ship takes 200,000 years to cross it.  Using the fifty-year delay to set up the next colony, the cross­ing time is about two mil­lion years.  If civ­i­liza­tions last hun­dreds of mil­lions of years, two mil­lion years seems less than daunting.

An impor­tant con­sid­er­a­tion of this idea is look­ing at the escape speed of a solar mass star.  The escape speed is the speed leav­ing the solar sys­tem deter­mined from Newton’s uni­ver­sal law of grav­i­ty.  That speed for our sun is 42.1 kilo­me­ters per sec­ond (km/s).  Let’s use that speed to trav­el a light year or 6 tril­lion kilo­me­ters (that is 6 with 12 zeros or 6x1012 km).  We find it takes nine thou­sand years to trav­el that distance.

A space­craft leav­ing at the escape speed of the sun will take longer than human civ­i­liza­tion has exist­ed to trav­el the dis­tance.  Scal­ing up to the size of the galaxy makes the jour­ney across the galaxy at 900 mil­lion years. With the uni­verse being 13.5 bil­lion years old, 900 mil­lion years is short.  Even the Earth, at 4.5 bil­lion years old, is old­er than the time it takes an object to cross the galaxy at 42.1 km/s—such a speed means it can hap­pen over four and a half times over the cur­rent age of the Earth.

We will con­sid­er the trav­el times com­put­ed in the last para­graph with great inter­est when we exam­ine pansper­mia in a future arti­cle.  We real­ize that a long lived (bil­lion-year plus) civ­i­liza­tion will cross the galaxy at an eas­i­ly attain­able speed.  The key point of the Fer­mi para­dox is that thor­ough­ly explor­ing a galaxy is doable in enough time.
As an emerg­ing civ­i­liza­tion, human­i­ty has sent probes on inter­stel­lar jour­neys (e.g. Voyager’s 1 and 2).  Humanity’s largest speeds are on order of 42 km/s, slow­er than the 300 thou­sand km/s of the speed of light.  Going faster makes the journey’s short­er.  And short­er dis­tances make the explo­ration of the galaxy eas­i­er.  So, we can con­tem­plate our even­tu­al explo­ration of the galaxy.  If we con­tem­plate it, why could not anoth­er alien civ­i­liza­tion con­tem­plate it?  If they could con­tem­plate it, why is there no evi­dence?  Hence, this is Fermi’s para­dox.  The first civ­i­liza­tion might ask: Are we alone?

A recent tele­vi­sion sci­ence fic­tion series revolved around a space­ship strand­ed on the far side of the galaxy after acci­den­tal­ly trav­el­ing through a worm­hole.  The space­ship esti­mat­ed that their jour­ney time back home to take sev­en­ty years—an aver­age speed of 1,429 times the speed of light.  The series last­ed sev­en years for them to return home—an aver­age speed of 14,290 times the speed of light.

We can con­tin­ue with the sci­ence fic­tion exam­ple. We need to deter­mine the time to explore all the solar sys­tems in the galaxy using their tech­nol­o­gy. We first assume a neg­li­gi­ble time to explore a solar sys­tem and the aver­age star sep­a­ra­tion of 4 light years. The jour­ney will explore twen­ty-five thou­sand solar sys­tems. They cross the entire breadth of the galaxy. Explor­ing four hun­dred-bil­lion solar sys­tems requires six­teen mil­lion ves­sels to com­plete the task.

To dou­ble the num­ber of space­ships, to reach 100 bil­lion requires you to dou­ble the num­ber thir­ty-sev­en times.  But the num­ber of dou­bling to reach 16 mil­lion is twen­ty-four.  Now it becomes a mat­ter of how rapid the dou­bling takes place. In our orig­i­nal exam­ple at half the speed of light and a fifty-year dou­bling time, it takes 1850 years to dou­ble to 100 bil­lion, or 1200 years to dou­ble to 16 mil­lion. The con­clu­sion for cal­cu­lat­ing the dou­bling times is to show that some­times, such as the half the speed of light, the speed of trav­el is lim­it­ing.  But, with the super­lu­mi­nal speeds, the abil­i­ty to build inter­stel­lar space­ships (AKA the dou­bling time) is limiting.

The main take-away from this arti­cle is that a civ­i­liza­tion capa­ble of a jour­ney to the stars can vis­it every solar sys­tem in the galaxy in a short time com­pared with cos­mic time scales.  A rea­son­able con­clu­sion based on the size of the galaxy; some civ­i­liza­tion would have made this effort.  The para­dox is why we haven’t found the evi­dence for that occurring—and if we cre­ate a sci­ence fic­tion uni­verse, what is the evidence?

As a sci­ence fic­tion world builder, the first deci­sion is how fast can a space­ship cross the galaxy.  This amounts to mak­ing a hard choice.  Is faster than light trav­el pos­si­ble?  Once we know the largest speed, we find the time it takes a civ­i­liza­tion to explore the galaxy com­plete­ly. There are more con­sid­er­a­tions beyond these, but they will wait for future articles.

In future arti­cles, we will revis­it the Fer­mi para­dox.  We’ll try to esti­mate the expan­sion rate of a civ­i­liza­tion across the galaxy and what this will mean if mul­ti­ple civ­i­liza­tions exist. We’ll exam­ine at the Fer­mi para­dox as it applies to pansper­mia.  Next time, we’ll look at the lev­els of civ­i­liza­tions based upon their tech­nol­o­gy.  We know it as the Kar­da­shev scale.

The Science of “Golf and Outgassing”

Repub­lished from APRIL 14, 2018

* SPOILER ALERT *

It’s dif­fi­cult to talk about the sci­ence involved in a sto­ry with­out actu­al­ly dis­cussing some of the aspects of the sto­ry. So as a fore­warn­ing, I rec­om­mend that you read the sto­ry first and come back to this arti­cle. I’ll con­tin­ue with the arti­cle in the next para­graph. The sto­ry Golf and Out­gassing is avail­able here.

* * * * * *

Golf and Out­gassing is a sto­ry regard­ing the return to the moon some­time in the next decade of an alter­nate his­to­ry.   It revolves around the land­ing site Fra Mau­ro, the loca­tion of the 1971 land­ing of Apol­lo 14 i ii. The title itself is sug­ges­tive of the event end­ing the two-day stay of Apol­lo 14 — Alan Shep­ard’s famous lunar golf shots iii. The out­gassing piece is from part of the pre­lim­i­nary sci­ence results for the mission.

Fra Mau­ro high­lands is a region on the east­ern edge of the Ocean of Storms, near the cen­ter of the disk of the full moon. It was select­ed because of the rel­a­tive­ly recent (and deep) impact crater called Cone Crater. Cone Crater seemed to be deep enough that it might have punched through the under­ly­ing sur­face geol­o­gy and blast­ed pieces of the bedrock dur­ing the impact. One of the sci­ence goals of Apol­lo 14 was to trav­el to the rim of Cone Crater and sam­ple the rocks from with­in. The bulk of the sec­ond EVA involved Alan Shep­ard and Edgar Mitchell work­ing their way up the Cone Crater slope iv v

The rest of the sci­ence back­ground for the Golf and Out­gassing sto­ry is the Apol­lo Lunar Sur­face Exper­i­men­tal Pack­age ALSEP vi. One of the ALSEP exper­i­ments detect­ed water vapor. This occurred weeks lat­er after Shep­pard and Mitchel had depart­ed the moon and returned to the earth. An exper­i­ment called the Suprather­mal Ion Detec­tor Exper­i­ment vii (SIDE) detect­ed the water sig­na­ture viii. It’s like­ly that the result was con­sid­ered void because of no equiv­a­lent event at anoth­er Apol­lo land­ing site. Also, the dry moon par­a­digm became stan­dard. It remained in effect until the Clemen­tine mis­sion sug­gest­ed oth­er­wise ix.

The crawler, or pres­sur­ized rover, is based on a vehi­cle that has been con­sid­ered by NASA as part of the can­celed Con­stel­la­tion pro­gram. It had been devel­oped as part of the desert rats exer­cis­es. The crawler’s capa­bil­i­ties enables lunar explo­ration in a shirt sleeve envi­ron­ment, leav­ing EVA’s to han­dle spe­cial cir­cum­stances that could not be han­dled by robot­ics x

The exis­tence of a sky­light cave struc­ture under Cone Crater is made up for pur­pos­es of the sto­ry. There are sky­light caves on the moon, dis­cov­ered by the Selene (a Japan­ese Lunar Mis­sion) xi They are expo­sures of sub-sur­face lava tubes. Like polar craters, a lava tube could act as a cold trap, allow­ing the volatile sub­stances such as water to accu­mu­late inside of the caves. The expla­na­tion that is inferred in “Golf and Out­gassing” is that the water detect­ed by the SIDE was from a cave con­cealed under Cone Crater that released vapor after the Apol­lo 14 mis­sion. If such a cave exist­ed, dis­cus­sion about return to the moon would like­ly include Fra Mauro.

Ref i: NASA Apol­lo 14 page. 

Ref ii: Wikipedia Apol­lo 14 page 

Ref iii: PGA News Lunar Golf Shots 

Ref iv: Fra Mau­ro land­ing site

Ref v: Report on Geol­o­gy of Fra Mauro 

Ref vi: Apol­lo 14 Sci­ence Experiments 

Ref vii: Suprather­mal Ion Detec­tor Experiment 

The Science of Morgan’s Road

 

Repub­lished from DECEMBER 14, 2017
* SPOILER ALERT *
It’s a lit­tle hard to talk about the sci­ence involved in a sto­ry with­out actu­al­ly dis­cussing some of the aspects of the sto­ry. So as a fore­warn­ing, I rec­om­mend that you read the sto­ry first and come back to this arti­cle. I’ll con­tin­ue with the arti­cle in the next para­graph. The sto­ry “Mor­gan’s Road” is avail­able here.

* * * * *

Mor­gan’s road began as a sto­ry about the lunar regolith. Regolith is essen­tial­ly lunar dust. Due to repeat­ed bom­bard­ment by objects rang­ing in size of moun­tains to micro­scop­ic grains, the moon’s soil has been beat­en down into tiny dusty grains. This dust is every­where, and as expe­ri­ence by the crews of the Apol­lo land­ings, it gets onto every­thing. Most of the sam­ple con­tain­ers returned to the moon did not seal prop­er­ly. Con­se­quent­ly, there was sig­nif­i­cant con­t­a­m­i­na­tion of the soil by the atmos­phere of the space­craft and lat­er the Earth­’s atmos­phere [1].

 

The moon’s lack of atmos­phere has ensured that any dis­tur­bance of the regolith will last for years. In fact, the dis­tur­bance in the regolith asso­ci­at­ed with the Apol­lo mis­sions remain to this day. The lunar recon­nais­sance orbiter LRO, imaged each of the Apol­lo land­ing sites, show­ing the tracks left by the astro­nauts and lunar rovers[2].   Morgan’s road is an exten­sion of this idea of long last­ing or per­ma­nent tracks. Nel­son will be able to track Mor­gan back to his secret – the ice that allows him to sur­vive on the moon. The tracks asso­ci­at­ed with Morgan’s crawler would be a per­ma­nent record of every place that Mor­gan vis­it­ed, includ­ing the source of the ice.

 

The moon held a secret until long after the Apol­lo mis­sions had con­clud­ed. In fact the sci­en­tif­ic par­a­digm of the era held for a dry moon. Use of radar from the Earth, and the flight of the Clemen­tine mis­sion past the moon revealed hints of water ice exist­ing in the per­ma­nent­ly shad­owed cre­ators of the lunar poles. Lat­er mis­sions, notably the LCROSS mis­sion con­firmed the dis­cov­ery [3].

 

Part of Morgan’s Road deals with the eco­nom­ics of space­flight in gen­er­al and lunar explo­ration specif­i­cal­ly by look­ing at the issue of Lunar sup­plies. Sup­pos­ing that water was nev­er dis­cov­ered on the moon, any water used by the peo­ple on the moon would have to be shipped there. Includ­ing water and oxy­gen, twen­ty five thou­sand pounds of sup­plies are need­ed to sup­port one per­son for one year on the moon. To put that in per­spec­tive, that is about the mass deliv­ered to the sur­face by the Apol­lo Lunar mod­ule. So, that would mean that the equiv­a­lent of a Sat­urn V launch every year to sup­port one per­son on the sur­face. To make this viable the sup­port costs need to be reduced by in situ resource uti­liza­tion ISRU [4] capa­bil­i­ty and the abil­i­ty to recy­cle the water [5].

 

In Morgan’s Road, Nel­son pays approx­i­mate­ly a hun­dred dol­lars a gal­lon for water. The price seems extreme, since enough water for a per­son to sur­vive a month would be fif­teen hun­dred dol­lars a month. This would seem almost unsus­tain­able for all but the rich­est indi­vid­u­als going to the moon on their own dime. But its even more finan­cial­ly dif­fi­cult than that. The price per gal­lon in Morgan’s road has to be heav­i­ly sub­si­dized. For exam­ple, to put a pound of pay­load on the moon for Apol­lo was over sev­en­ty thou­sand dol­lars. So at ten pounds per gal­lon, it would cost Apol­lo sev­en hun­dred thou­sand dol­lars to ship a gal­lon of water to the moon. Even the most aggres­sive schemes in the mod­ern era sug­gest that the price per pound to the sur­face of the moon would be about a thou­sand dol­lars.  Morgan’s Road shows that unless there is a sig­nif­i­cant shift of the bur­den of resource man­age­ment, an unsup­port­ed pop­u­la­tion on the lunar sur­face is dif­fi­cult to achieve.

 

Though it makes for a good sto­ry, Morgan’s secret is hard­ly a secret to us. The moon has water and some inter­est­ing mech­a­nisms for gath­er­ing it. It also has been a sur­prise to find water in the lunar soil at equa­to­r­i­al lat­i­tudes. This dis­cov­ery, using the moon min­er­al­o­gy map­per and the Cassi­ni space probe, changed all per­cep­tions of the moon. The exis­tence of this water is a major game chang­er for the eco­nom­ics of space flight [6]. The water can be used to make pro­pel­lant, which in turn changes the cost func­tion for activ­i­ties in cis­lu­nar space, since that pro­pel­lant does not come from Earth.

References:

  1.  https://www.hq.nasa.gov/alsj/TM-2005–213610.pdf

  2.  https://www.nasa.gov/mission_pages/LRO/news/apollo-11.html

  3.  http://“https://www.nasa.gov/mission_pages/LCROSS/main/prelim_water_results.html

  4.  https://www.nasa.gov/exploration/analogs/isru/

  5.  https://www.nasa.gov/content/water-recycling

  6.  https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930004795.pdf