Origin of life

Fora ASTRO-FORUM NYT FRA VIDENSKABEN Origin of life

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  • #316584
    Bjarne
    Bjarne
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    • Super Nova

    Jack W. Szostaks ON THE ORIGIN OF LIFE er den korteste beskrivelse af en kemisk vej mod en RNA protocelle:

    Jack W. Szostak: ON THE ORIGIN OF LIFE

    Szostaks otte trin mod en udviklende RNA protocelle.

     

    #316601
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg er blevet opmærksom på IAU Symposium 345: From the Protosun to the First Steps of Life:

    The symposium will take place in Vienna at the 30th IAU General Assembly

    We are pleased to announce the following invited speakers, who will lead the main sessions:

    Mike Juvela (Finland): Star Formation in the solar neighborhood — surveys, generalities, simulations
    Christoph Federrath (Australia): Star formation in cloud cores – simulations and observations of dense molecular cores and the formation of solar mass stars
    Edward Young (USA): Early environment of the pre-solar nebula – isotopic anomalies in meteorites and the implications for nearby supernovae; physics of presolar nebulae, single versus binary star formation
    Laura Perez (Chile): Formation and evolution of protoplanetary disks – observations and modeling of jets, disks, and disk substructures
    Inga Kamp (Netherlands): Physical and chemical properties of protoplanetary disks – chemical composition, organics, planetesimals, planetary embryos; snow line; complex molecules; temperatures and densities; magnetic fields
    Eiichiro Kokubo (Japan): Formation of Earth and Earth-like planets
    Doris Breuer (Germany): Early planetary atmospheres and surfaces, origin of the Earth’s water, crust and atmosphere
    Helmut Lammer (Austria): Early conditions on the Earth; general conditions for habitability – young stellar output, stellar winds and activity
    Daniel Apai (USA): Earth-like planets – observations, properties
    Addy Pross (Israel): Early life on Earth – tracing the physical/chemical process from non-living to living

    Jeg bemærker især Addy Pross, som har skrevet en bog om emnet:

    What is Life?

    Reconsiders the big question: how did life emerge from non-life?
    Draws on recent results from the new field of systems chemistry to articulate an answer
    Shows how chemical systems become complex and acquire the properties of life
    Demonstrates that Darwinian evolution is the expression of a much deeper principle in the physical sciences
    With a new Epilogue highlighting the latest developments in the ideas discussed, and their implications
    Part of the Oxford Landmark Science range: ‘must-read’ modern science and big ideas, which have shaped the way we think.

    Bogen er en moderne opfølger til Schrodingers berømte bog af samme navn (fra 1944)

    Jeg køber begge bøger fra Amazon.

    Seventy years ago, Erwin Schrodinger posed a profound question: ‘What is life, and how did it emerge from non-life?’ This problem has puzzled biologists and physical scientists ever since.

    Living things are hugely complex and have unique properties, such as self-maintenance and apparently purposeful behaviour which we do not see in inert matter. So how does chemistry give rise to biology? What could have led the first replicating molecules up such a path? Now, developments in the emerging field of ‘systems chemistry’ are unlocking the problem. Addy Pross shows how the different kind of stability that operates among replicating molecules results in a tendency for chemical systems to become more complex and acquire the properties of life. Strikingly, he demonstrates that Darwinian evolution is the biological expression of a deeper, well-defined chemical concept: the whole story from replicating molecules to complex life is one continuous process governed by an underlying physical principle. The gulf between biology and the physical sciences is finally becoming bridged.

    This new edition includes an Epilogue describing developments in the concepts of fundamental forms of stability discussed in the book, and their profound implications.

    Jeg er tilhænger af anvendelsen af fysiske principper, men spørgsmålet er, om de kan forklare fremkomsten af celler med membraner.

     

    #316790
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg har modtaget Addy Pross’ bog What is Life, og jeg har læst første kapitet: Living things are so very stranges, set ud fra en fysikers synspunkt. Der er en bred kløft mellem en fysikers beskrivelse af den fysiske verden og en biologs beskrivelse af den levende verden. Hvis man skal give kløften et enkelt navn, er det begrebet Entropi. Navnet blev opfundet i 1865 af Rudolf Clausius, som en grænse for den nyttige mekaniske energi, som kan trækkes ud af varmeenergi, som flyder fra et varmt sted til et koldt sted. Sætningen siger, at den totale entropi for et isoleret system altid må vokse. Ludwig Boltzmann gav i det næste årti entropien en statistisk forklaring. Formlen for entropien for et fysisk system i termisk ligevægt står på Boltzmanns gravsten: S = k ln W, hvor W er antallet af måder, hvorpå det makroskopiske system kan realisetes. k er en konstant opkaldt efter Boltzmann. W er et udtryk for systemets sandsynlighed. Et isoleret system udvikler sig altid mod en større sandsynlighed, altså fra det mindre sandsynlige mod det mere sandsynlige.

    Selv den mest primitive levende celle er en molekylær nano-fabrik styret af et program lagret i DNA molekylet. Fabrikkens kemiske processer udføres af enzymer, som består af foldede kæder af aminosyrer i en ganske bestemt rækkefølde, som bestemmes af DNA molekylet. Det er her helt afgørende at forstå, at loven om entropiens vækst også gælder for RNA (ribonukleinsyre) molekylet, såvel som for de foldede enzymer. Den korrekte kopiering af RNA informationen kræver en fejlkorrektion ved specielle enzymer. Selv enzymerne mister hurtigt deres funktionsevne, så cellens enzymfabrik ribosomet reproducerer cellens enzymer hver time! Denne oplysning var ny for mig. Cellen består altså af nogle helt andre molekyler efter nogle få timer. Ribosomet har ikke udviklet sig under den naturlige udvælgelse. Sandsynligheden for at finde en levende celle som en tilfældighed er enormt lille selv med en logaritme foran.

    Den levende celle har en enormt lav entropi, men den er alligevel i en kontrolleret ligevægt. Dette strider mod alt, som en fysiker har lært. Hvordan kan et livløst molekylært system bevæge sig mod lavere og lavere entropi, så det ender på den anden side af kløften? Et molekyle er et kvantemekanisk system af atomer med elektroner. En levende celle er en molekylær fabrik, som også opfylder de kvantemekaniske love. Findes der en speciel lovmæssighed, som tillader, at et stort molekylært system at bevæge sig i ligevægt mod større og større organisering? Forfatteren skriver, at han vil afsløre omridset til en sådan hidtil overset lovmæssighed. Jeg læser videre med en vis skepsis.

    #317065
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg beklager, at læsningen går lidt langsom på grund af andre ting. Bogen fortæller, at ideen om livets træ baseret på den sidste universelle fælles stam-fader/moder (LUCA) er forkert. Træet blev udledt ud fra ribosomets RNA og enzymer under den antagelse, at generne arves af afkommet. Den totale genomsekvens viser imidlertid, at gener også udvikles horisontalt mellem arterne. Så livets træ er et resultat af antagelserne. Det er mere korrekt at kalde udvikling for livets spind eller Web of Life. Den første celles sande struktur forsvinder derfor i tågerne.

    Addy Pross mener, at det er en stor fejl at fokusere så meget på de kemiske forbindelser på den tidlige jord og andre planeter. En kemiker ville alligevel ikke være i stand til at konstruere en levende organisme ud fra de nødvendige byggesten. Nutidens organismer er alt for komplicerede. Man mangler et princip, som kan udvikle et kemisk system mod større og større termisk uligevægt (mindre entropi), indtil der dannes et kemisk system, som kan reprocucere og udvikle sig ved mutationer. Det er håbet, at man i laboratoriet kan udvikle en kunstig livsform, som er meget simplere en nutidens livsformer. En sådan livsform vil kunne udvikle sig efter Darwins principper.

    Hvis man selv kan udvikle en primitiv kemisk livsform, vil man meget bedre kunne forstå mulige livsformer på andre planeter. Jeg rapporterer, når jeg har fået læst de sidste to kapitler. Men der er ingen garanti for succes.

    #317091
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg har med en del besvær fundet denne artikel i Open Biology, som i nogen større teknisk detalje forklarer Addy Pross’ ideer om overgangen fra kemi til biologi:

    Towards an evolutionary theory of the origin of life based on kinetics and thermodynamics

    Abstract

    A sudden transition in a system from an inanimate state to the living state—defined on the basis of present day living organisms—would constitute a highly unlikely event hardly predictable from physical laws. From this uncontroversial idea, a self-consistent representation of the origin of life process is built up, which is based on the possibility of a series of intermediate stages. This approach requires a particular kind of stability for these stages—dynamic kinetic stability (DKS)—which is not usually observed in regular chemistry, and which is reflected in the persistence of entities capable of self-reproduction. The necessary connection of this kinetic behaviour with far-from-equilibrium thermodynamic conditions is emphasized and this leads to an evolutionary view for the origin of life in which multiplying entities must be associated with the dissipation of free energy. Any kind of entity involved in this process has to pay the energetic cost of irreversibility, but, by doing so, the contingent emergence of new functions is made feasible. The consequences of these views on the studies of processes by which life can emerge are inferred.

    2. Introduction

    The problem of the origin of life can be approached from two directions; from biology back or from chemistry forward. From biology back, Darwin proposed his Doctrine of Common Descent: ‘Probably all of the organic beings which have ever lived on this Earth have descended from some one primordial form…’. Woese pointed out that prior to a ‘Darwinian threshold’ being crossed, the earliest life was probably communal with extensive exchange of coded cellular componentry. The origin of this communal life is presumed to have occurred on the early Earth but a precise description of the transition from chemistry to biology will remain out of reach looking back from early living forms because very rudimentary life forms made of unstable organics are unlikely to leave fossil remains. Alternatively, from chemistry forward, the question of the transition may be explored as that of self-organization in chemical systems both through experimental and theoretical approaches. This approach connects with the requirement that the process must obey physical and chemical laws in the same way that life has been demonstrated to do, which is especially critical when considering metabolism, the way in which ‘living matter evades the decay to equilibrium’.

    The literature of the past 60 years is rich in publications reporting progress through both of these approaches. However, there is still no generally accepted model of the process that could lead to the emergence of life. We share the conviction that general theoretical insights into this evolutionary process can presently be identified without its details having to be disclosed, and we try to summarize the main principles governing this process. We also consider that these views constitute a basis by which systems chemistry can expand knowledge in this field unimpeded by historical constraints and potentially able to provide experimental examples of systems manifesting at least some of the features corresponding to those of the living state.

    3. The improbability of life

    The elucidation of the double helical structure of DNA 60 years ago provided a molecular explanation for the transmission of genetic information that accompanies cell division. But this breakthrough also prompted a series of discoveries, including that of the genetic code, revealing how nucleic acid sequences are translated into protein sequences using trinucleotide coding of amino acids. At that time, the main bases of biochemistry appeared to be understood and Monod developed a philosophy of biology deduced from all the knowledge that was acquired within two decades that gave a molecular interpretation of the Darwinian theory of evolution proposed a century before. Combined with evolutionary processes, these thoughts provided a profound insight into the most puzzling facets of living organisms, but gave no definitive characterization of the processes by which life originated. As a matter of fact, Monod resorted to a highly improbable random event generating a system possessing essentially all of the basic features of life in one step to explain the origin of life on our planet, and considered it therefore had to be an exception in the universe. If we comply with a probabilistic description of this event, it is possible to set loose limits on its likelihood by considering, for example, the random formation of biopolymeric components, for instance nucleic acids, from their building blocks. The probability of a single sequence of 50 nucleotides among all possibilities corresponds to 1/450 ≈ 0.8×10–30 meaning that the exploration of the complete set of sequences over 1 billion years would require the synthesis of more than 4 ×1013 different sequences every second. If we consider now that a sequence made up of 100 monomers was needed for a ribozyme to have the wide range of activity allowing the polymerization of the four ribonucleotides, the probability of one single sequence would be reduced to 0.6×10–60 and synthesizing all of them in one molecular unit over 1 billion years would lead to the synthesis of a mass of nucleic acid representing several tens that of the Earth per day. These simple virtual calculations clarify how improbable could be the emergence of even a single RNA strand capable of some sort of ribozyme activity within Monod’s first living organism, which corresponds to the situation proposed in a: a sudden transition from an inert state to the living state. This possibility seems virtually unattainable and it is hardly possible to state as scientific the investigation of a process that is considered as non-reproducible, thus invalidating any experimental study aimed at reproducing the origin of a life form. We thus face a dilemma; either Monod was right, life emerged as a consequence of an event that had almost no chance to occur during the lifetime of the universe, or the emergence of life is not a mere question of the probability of a single event, but a driving force exists—and can thus be discovered—to drive this process through its various stages. So the second possibility—the existence of some driving force governing the evolutionary process—needs to be investigated. It is axiomatic therefore that any scientific study of the origin of life must start from the principle that the transition towards life took place through non-zero probability events, and according to this principle, life would have emerged stepwise, through states of partial ‘aliveness’, rather than through some single sharp transition, as recently discussed by Bruylants et al. . Events, considered individually as having a non-zero, albeit possibly low probability, can then be strung together to constitute an evolutionary process avoiding any violation of this principle. A consequence of viewing the origin of life as a sequence of events rather than a single transition is that ‘a clear-cut frontier between a non-living state of matter and a living system’ becomes impossible. Choosing among the multiple steps in the process and choosing a clear limit separating the living world from inert things becomes a philosophical issue rather than a scientific one.

    Follow link to read more.

    • Dette svar blev ændret 5 måneder, 4 uger siden af Bjarne.
    • Dette svar blev ændret 5 måneder, 4 uger siden af Bjarne.
    #317096
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Artiklen konkluderer ikke med en ligning for livets oprindelse. Dette er ikke en tilfældighed. Formålet er at opstille regler for autokatalytiske kemiske systemer, som er analoge til reglerne for biologiske systemer.

    De kristne fundamentalister i USA fremfører argumentet: Darwins udviklingslære er kun en teori. Dette er imidlertid en fundamental fejltagelse. Darwins lære om arternes oprindelse er ikke en teori!

    Lovmæssigheder i biologi og økonomi baserer sig på Sir Francis Bacons induktive metode. Hvem var Francis Bacon? Han var blandt meget andet juridisk rådgiver for Elizabeth I. Induktiv betyder på almindeligt dansk: Anvendelse af eksperimentelle målinger til at gætte sig til en matematisk sammenhæng. Udledningen er på ingen måde baseret på logik. Lovmæssighedernes sandhedsværdi skal derfor til stadighed afprøves med nye og bedre målinger.

    Her er et par eksempler: a) Keplers love udledt ud fra målinger af marsbanens form, b) anvendelsen af det kopernikanske princip til at postulere spontan skabelse af liv overalt. a) blev anvendt af Newton til at udlede teorien for den universelle lov for tyngdekraften fra en punktmasse. b) blev 300 år senere modbevist af Pasteur, som dermed blev årsag til de store problemer med livets oprindelse.

    Men hvad er så en teori? En teori er en deduktiv hypotese, som logisk kan udledes ud fra nogle få axiomer/definitioner, og som kan forudsige systemets fremtidige udvikling ud fra den nuværende tilstand (et godt stykke ud i fremtiden). Man kan med en vis ret sige, at man har forstået et system, hvis der findes en teori for systemet.

    Det er pludseligt gået op for mig, hvorfor eksaminator i det nye karaktersystem ikke må undersøge, om eksaminanden har forstået stoffet. Det har altid forekommet mig en gåde, hvorfor eksaminator kun må undersøge, om eksaminanden kan beskrive stoffet.

    Eksamenskommisionen blev ledet af Kathrine Richardson, som er biolog, og læringsmålene blev udarbejdet af OECD, dvs af økonomer. Nå, dette var lidt af et sidespring, men det viser, at der er en dyb kløft mellem fysik og biologi. Addy Pross’ mission er at bygge bro over denne kløft ved at anvende biologiske lovmæssigheder på selvkopierende kemiske systemer. Det er derfor indlysende, at kløften kun kan overvindes ved eksperimenter.

    #317097
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg glemte at forklare, hvorfor den biologiske udvikling ikke kan forklares ved en teori, dvs en deterministisk udvikling. Forklaringen er ganske simpel. Arternes udvikling skyldes små tilfældige mutationer i generne. Tilfældige ændringer kan ikke forudsiges ved en deterministisk teori. Arternes udvikling kan ikke forudsiges. Det er et samspil mellem mutationer og miljø. Udviklingen af et selv-kopierende kemisk system er også drevet som et samspil mellem tilfældige mutationer og et miljø af de monomere byggesten. Udviklingen kan derfor heller ikke her forudsiges deterministisk.

    #317106
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Der er i mellemtide udkommet en artikel i Science, som direkte viser, at en bakteries celledeling producerer spontane mutationer med en konstant rate. Man kan derfor ikke forudsige et biologisk systems udvikling deterministisk:

    Mutating DNA caught on film

    DNA mutations cause tumor cells to grow out of control, but they also generate variety that enables organisms to adapt to their environments and evolve. Until now, biologists have only had crude methods for estimating the average rates and effects of mutations. But in a new study, biophysicists have documented individual mutations as they happen in bacterial cells.

    These changes occur at about the same rate over time—as opposed to in bursts—and only about 1% are deadly, the researchers report today in Science. Moreover, all bacteria in a given strain seem to have about the same mutation rate—about one mutation per 600 hours in normal bacteria, and about 200 mutations per 600 hours in bacteria engineered to mutate at a faster rate—they note.

    To see the mutations, the team built 1000 microscopic channels into a computerlike chip and placed a single bacterial cell at the closed end of each the channel, along with plenty of nutrients to survive. The bacteria carried a modified DNA repair protein that caused any mutations to glow yellow. Then, for 8 hours up to 3 days, the researchers took a picture every few minutes as new bacterial cells were formed, pushed down the channel, and then swept away by fluid flowing across the ends of these channels. Automated image processing let them count the number of mutations and assess how well the cells were doing. Dead cells signaled a deadly mutation; slower growing cells signaled a detrimental change.

    According to its developers, the technique can be applied to assess mutation dynamics in other types of cells, even human cancer cells. And the researchers eventually hope to be able to monitor mutation rates real time in entire organisms, such as zebra fish, to see whether different tissues have different mutation rates.

    Dette viser tydeligt, at et biologisk systems udvikling ikke kan beskrives ved en deduktiv hypotese, som forudsiger den fremtidige tilstand ud fra den øjeblikkelige tilstand. Denne type hypoteser er ifølge Poincare en teori. Et biologisk system kan kun beskrives ved en induktiv hypotese, som er en statistisk relation fundet ud fra måledata. En induktiv hypotese giver ikke en årsagssammenhæng.

    Addy Pross skaber i bogen total forvirring omkring betydningen af ordet teori. Han bruger betegnelsen “Darwins teori”. Jeg må indrømme, at jeg på dette punkt selv var ret forvirret. Men så kom meddelelsen om det kraftige globale 21cm-signal ved rødforskydningen z=17. Dette blev omtalt som en anomali. Jeg kom i tanke om gamle anomalier i forbindelse med skivegalaksers rotationskurver. Hvad er en anomali egentlig? Det er her nødvendigt at opsøge videnskabsfilosoffer, som anvender Poincares klassifikation af videnskabelige hypoteser. En anomali optræder, hvis måledata afviger fra en teoris forudsigelser. Anomalier forekommer ikke i forbindelse med induktive love, da disse ikke er forudsigelser, men kun statistiske relationer. Darwins udviklingslære kan derfor umuligt være en teori.

    • Dette svar blev ændret 6 måneder, 1 uge siden af Bjarne.
    • Dette svar blev ændret 6 måneder, 1 uge siden af Bjarne.
    #317119
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Forvirringen om induktive og deduktive (teoretiske) hypoteser i biologien fortsætter. I slutningen af bogen skriver Addy Pross: “The extraordinary powers of science and the inductive method in particular, have revolutionized our lives and our understanding of theworld”. I en epilog til bogen angiver han “one governing rule — the persistence principle”. Pross: “The view of biology as a separate science with a special methodology and philosophy of science, in vogue for much of the past century, can be confidently dismissed”. Biologiens specielle filosofiske metode bygger på, at dens love er baseret på induktive hypoteser. Er denne nye “åbenbaring” et udtryk for, at Darwins udviklingslære kan forudsiges af deduktive hypoteser? Hvad er argumentet?

    Pross: “there happen to be (to the best of our knowledge) just two mathematical formulations that stipulate in logical terms how increasingly persistent forms can come about — Boltzmann’s probabilistic way and Malthus’ exponential growth way”. Jeg kan godt forestille mig, at de koblede differentialligninger, som beskriver disse to principper kan udsættes for en teoretisk analyse, men hvor kommer de spontane mutationer ind i analysen? Grunden til, at biologiske systemer ikke kan forudsiges ved en deduktiv hypotese er netop, at mutationerne er tilfældige. Jeg har fundet denne artikel af Robert Pascal og Addy Pross:

    Stability and its manifestation in the chemical and biological worlds

    Bridging between the phenomenologically distinct biological and physical worlds has been a major scientific challenge since Boltzmann’s probabilistic formulation of the second law of thermodynamics. In this review we summarize our recent theoretical attempts to bridge that divide through analysis of the thermodynamic-kinetic interplay in chemical processes and the manner in which that interplay impacts on material stability. Key findings are that the term ‘stability’ manifests two facets – time and energy – and that stability’s time facet, expressed as persistence, is more general than its energy facet. That idea, together with the proposed existence of a logical law of nature, the persistence principle, leads to the mathematically-based insight that stability can come about through either Boltzmann’s probabilistic considerations or Malthusian kinetics. Two mathematically-based forms of material persistence then lead directly to the physical likelihood of two material forms, animate and inanimate. Significantly, the incorporation of kinetic considerations into the stability concept appears to bring us closer to enabling two of the central theories in science – the second law of thermodynamics and Darwin’s theory of evolution – to be reconciled within a single conceptual framework.

    Jeg har ikke læst artiklen, men den har tilsyneladende ingen formler. Jeg lægger måske for meget i formuleringerne. Biologien har måske både deduktive og tilfældige aspekter.

    • Dette svar blev ændret 6 måneder, 1 uge siden af Bjarne.
    • Dette svar blev ændret 6 måneder, 1 uge siden af Bjarne.
    #317133
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Ja, det er gået op for mig, at biologi er et fag, som spænder lige fra encellede organismer over planter og dyr til økologiske systemer med mange forskellige arter. Bogens erklærede mål var at bygge en bro over kløften mellem præbiotisk kemi til den simpleste encellede organisme. Antagelsen er, at overgangen er foregået via små skridt. Bogens mission er at finde fælles træk for bræbiotisk kemi og kemien i en encellet organisme. Det giver f.eks. ingen mening at finde de fælles træk for præbiotisk kemi og en giraf. En simpel celle kan beskrives som et selvkopierende (med mutationer) netværk af katalytiske kemiske reaktioner. Netværket befinder sig i en vedvarende tilstand langt fra termodynamisk ligevægt (lig med død). Dette er kun muligt, hvis der til stadighed tilføres cellen energi. De katalytiske evner nedbrydes hurtigt med tiden, så organismen ville hurtigt dø, hvis de katalytiske molekyler ikke hele tiden blev udskiftet. Det er autokatalytiske molekyler, som hurtigt bringer systemet langt fra termodynamisk ligevægt. Et autokatalytisk molekyle katalyserer sin egen dannelse, så antallet af molekyler vil vokse eksponentielt. (effekten ligner meget universets inflationsfase).

    Et præbiotisk kemisk system på vej mod en levende tilstand må derfor have de samme egenskaber. Det må bestå af et selvkopierende (med kopifejl) netværk af autokatalytiske kemiske reaktioner under tilførsel af energi. Hvis man i laboratoriet kan udføre et kemisk eksperiment, som ender med at have disse egenskaber, er man godt på vej til at forstå livets oprindelse. Biologien for en enkelt celles deling er ikke deduktiv og deterministisk, da mutationerne under celledelingen er telfældige. Det samme er tilfældet for det kemiske eksperiment på grund af kopifejlene, som også er tilfældige. Jeg kan helt gå ind for bogens konklusion, men så kom der en senere epilog.

    #317135
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Men så udkom artiklen i 2015, som hæver, at Darwins udviklingslære kan forklares ved en deduktiv og logisk teori på lige fod med den teoretiske fysiks love. Mutationer omtales slet ikke. Jeg vil citere konklusionen:

    The unorthodox conclusion which follows: that the living state, far from being a mysterious and seemingly inexplicable material state of matter, may be understood as a logically predictable state, no more phenomenological puzzling than the established and ubiquitous physical state of matter – solid, liquid and gas.

    Dette lyder unægteligt mærkeligt. Hvis den biologiske tilstand er teoretisk deterministisk, burde overgangen fra præbiotisk kemi til den biologiske tilstand være en simpel teoretisk sag. Men artiklen hævder, at overgangen fra kemi til et system med simple levende egenskaber stadig er et meget stort problem: Til now chemists have been unable to generate persistent chemical replicating systems of any kind, though van Esch et al. have been able to generate experimental dynamic non-equilibrium systems, though not replicative in nature.

    Forklaringen er sandsynligvis, at arternes udvikling er en økologist teori, hvor de enkelte elementer er dyr og planter, ikke katalytiske molekyler. Enkelte mutationer har en minimal betydning for en arts funktion i et økosystem, hvorimod en enkelt mutation i en bakteries genom har en langt større betydning for bakteriens stofskifte.

    Forfatterne omtaler til slut betydningen for astrobiologien: Until we better understand the detailed chemical character of replicative chemistry — how readily replicative systems are able to emerge from diverse chemical environments, and then how readily these systems can evolve — the answer to that tantalizing ‘are we alone’ question wil likely remain out of reach.

    En noget nedslående konklusion.

    #317204
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Vi er stadig lige uafklarede om de to ekstreme muligheder: (a) Livet er opstået ved en helt usandsynlig tilfældighed, så det kun findes på Jorden eller (b) Der findes en endnu ikke opdaget kemisk vej mod et selvkopierende netværk af kemiske processer, som i små skridt under tilførsel af energi kan udvikle sig til en encellet organisme. Dette er grunden til, at alle igangværende projekter søger efter beboelige planeter. Det er kun SETI, som springer de biokemiske processer over og søger direkte efter intelligent liv.

    Jeg køber en ret ny bog af Charles S. Cockell med titlen “Astrobiology: Understanding Life in the Universe”. Jeg bemærker ordet “Understanding” i titlen. Jeg er spændt på at se, om forfatteren kender Poincares skelnen mellem deduktive og induktive hypoteser.

    #317222
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Gaian bottlenecks and planetary habitability maintained by evolving model biospheres: The ExoGaia model

    The search for habitable exoplanets inspires the question – how do habitable planets form? Planet habitability models traditionally focus on abiotic processes and neglect a biotic response to changing conditions on an inhabited planet. The Gaia hypothesis postulates that life influences the Earth’s feedback mechanisms to form a self-regulating system, and hence that life can maintain habitable conditions on its host planet. If life has a strong influence, it will have a role in determining a planet’s habitability over time. We present the ExoGaia model – a model of simple ‘planets’ host to evolving microbial biospheres. Microbes interact with their host planet via consumption and excretion of atmospheric chemicals. Model planets orbit a ‘star’ which provides incoming radiation, and atmospheric chemicals have either an albedo, or a heat-trapping property. Planetary temperatures can therefore be altered by microbes via their metabolisms. We seed multiple model planets with life while their atmospheres are still forming and find that the microbial biospheres are, under suitable conditions, generally able to prevent the host planets from reaching inhospitable temperatures, as would happen on a lifeless planet. We find that the underlying geochemistry plays a strong role in determining long-term habitability prospects of a planet. We find five distinct classes of model planets, including clear examples of ‘Gaian bottlenecks’ – a phenomenon whereby life either rapidly goes extinct leaving an inhospitable planet, or survives indefinitely maintaining planetary habitability. These results suggest that life might play a crucial role in determining the long-term habitability of planets.

    Disse ideer er identiske med artiklen af Robert Pascal og Addy Pross om en deduktiv, logisk udvikling af et økologisk system.

    Men man kommer selvfølgelig ikke nærmere på en forståelse af overgangen fra kemi til den første celle.

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    #317269
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Biosfærens information i den samlede mængde DNA er blevet anslået i en artikel, som jeg tilfældigt faldt over. Den samlede kopihastighed er også blevet anslået og sammenlignet med tidens hurtigste supercomputere.

    An Estimate of the Total DNA in the Biosphere

    Modern whole-organism genome analysis, in combination with biomass estimates, allows us to estimate a lower bound on the total information content in the biosphere: 5.3 × 1031 (±3.6 × 1031) megabases (Mb) of DNA. Given conservative estimates regarding DNA transcription rates, this information content suggests biosphere processing speeds exceeding yottaNOPS values (1024 Nucleotide Operations Per Second). Although prokaryotes evolved at least 3 billion years before plants and animals, we find that the information content of prokaryotes is similar to plants and animals at the present day. This information-based approach offers a new way to quantify anthropogenic and natural processes in the biosphere and its information diversity over time.

    The Total DNA in the Biosphere

    Using information on the typical mass per cell for each domain and group and the genome size, we estimate the total amount of DNA in the biosphere to be 5.3 × 1031 (±3.6 × 1031) megabase pairs (Mb). This quantity corresponds to approximately 5 × 1010 tonnes of DNA, assuming that 978 Mb of DNA is equivalent to one picogram. Assuming the commonly used density for DNA of 1.7 g/cm3, then this DNA is equivalent to the volume of approximately 1 billion standard (6.1 × 2.44 × 2.44 m) shipping containers. The DNA is incorporated within approximately 2 × 1012 tonnes of biomass and approximately 5 × 1030 living cells, the latter dominated by prokaryotes. By analogy, it would require 1021 computers with the mean storage capacity of the world’s four most powerful supercomputers (Tianhe-2, Titan, Sequoia, and K computer) to store this information.

    The Computational Power of the Biosphere

    Finding the amount of DNA in the biosphere enables an estimate of the computational speed of the biosphere, in terms of the number of bases transcribed per second, or Nucleotide Operations Per Second (NOPS), analogous to the Floating-point Operations Per Second (FLOPS) metric used in electronic computing. A typical speed of DNA transcription is 18–42 bases per second for RNA polymerase II to travel along chromatin templates and elsewhere suggested as 100 bases per second. Precisely how much of the DNA on Earth is being transcribed at any one time is unknown. The percentage of any given genome being transcribed at any given time depends on the reproductive and physiological state of organisms, and at the current time we cannot reliably estimate this for all life on Earth. If all the DNA in the biosphere was being transcribed at these reported rates, taking an estimated transcription rate of 30 bases per second, then the potential computational power of the biosphere would be approximately 1015 yottaNOPS (yotta = 1024), about 1022 times more processing power than the Tianhe-2 supercomputer, which has a processing power on the order of 105 teraFLOPS (tera = 1012). It is estimated that at 37°C, about 25% of Open Reading Frames in Escherichia coli are being transcribed, but this is in a metabolically active population. In the natural environment, the percentage of DNA being transcribed is likely to be much less. Nevertheless, it is clear that even if the total DNA in the biosphere being transcribed at any given time was orders of magnitude less, the biosphere has many orders of magnitude more computational power than the fastest electronic computers yet built.

     

    #317274
    Bjarne
    Bjarne
    Moderator
    • Super Nova

    Jeg har medtaget dette indlæg af to grunde: (a) Eksponentiel vækst under tilførsel af energi er en absolut nødvendighed, hvis et netværk af kemiske reaktioner skal kunne udvikle sig mod negativ entropi og en kvasistabil tilstand, som man forstår ved liv. (b) Ray Kurzweil påstår, at en eksponentiel vækst i den kunstige intelligens kvalitet i løbet af blot 30 år vil udvikle sig til en superintelligens, som ikke længere er baseretr på biokemi. Denne udviklings eksponentielle vækst omtales som en singularitet, der medfører “disruption” af alle kendte forestillinger om den fysiske verden. Forestillingen om en accelererende eksponentiel vækst i kunstig intelligens har fascineret verdens økonomer, herunder Danmarks statsminister, som mange sikkert har bemærket.

    The Singularity Is Near: When Humans Transcend Biology

    En bog af Ray Kurzweil om kunstig intelligens. Endemålet kan hurtigt forklares ved Kurzweils svar på spørgsmålet: Does God exist? Not yet!

    Bogen omhandler i virkeligheden “Livets oprindelse” og intelligensens efterfølgende frigørelse fra biologi og kemi.

    Kurzweil says the law of accelerating returns suggests that once a civilization develops primitive mechanical technologies, it is only a few centuries before they achieve everything outlined in the book, at which point it will start expanding outward, saturating the universe with intelligence. Since people have found no evidence of other civilizations, Kurzweil believes humans are likely alone in the universe. Thus Kurzweil concludes it is humanity’s destiny to do the saturating, enlisting all matter and energy in the process.

    Sådanne ideer er ikke nye inden for Science Fiction. SF-forfatteren:

    Vernor Steffen Vinge

    opfandt begrebet “The Coming Technological Singularity“.

    The 2010s public figures such as Stephen Hawking and Elon Musk expressed concern that full artificial intelligence could result in human extinction. The consequences of the singularity and its potential benefit or harm to the human race have been hotly debated.

    Man kan her læse mere om

    Raymond “Ray” Kurzweil

    Man kunne affærdige sådanne ideer som luftige spekulationer om livets videre udvikling, hvis ikke en græsk læge og opfinder

    Peter H. Diamandis

    havde startet en bevægelse omkring Ray Kurzweils ideer om eksponentiel vækst:

    Singularity University

    In 2015, Singularity University and Yunus Social Business (YSB) announced a partnership at the World Economic Forum to use “accelerating technologies” and social entrepreneurship for global development in developing areas of the world where YSB is active.

    Her er World Economic Forum særlig interessant:

    The forum is best known for its annual meeting at the end of January in Davos, a mountain resort in Graubünden, in the eastern Alps region of Switzerland. The meeting brings together some 2,500 top business leaders, international political leaders, economists, celebrities and journalists for up to four days to discuss the most pressing issues facing the world. Often this location alone is used to identify meetings, participation, and participants, with such phrases as “a Davos panel” and “Davos man” being used.

    Det er altså det erklærede formål med “Singularity University” at overbevise verdens ledere og økonomer om, at den kunstige intelligens inden for de kommende 30 år vil forvandle menneskeheden til Gud eller udslette menneskeheden, hvis Elon Musk har ret.

    Her er så den officielle hjemmeside for Singularity University:

    Preparing Global Leaders & Organizations for the Future

    Denne forbløffende historie minder om en anden Science Fiction fortatter:

    Lafayette Ronald Hubbard

    som endte med at starte

    The Church of Scientology

     

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