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Wat is swaartekrag regtig?

Wat is swaartekrag regtig?


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Wat is swaartekrag? Ek wil meer weet as dat dit bloot die 'misterieuse krag' is wat dinge na die aarde lok. Is dit 'n deeltjie, 'n golf of iets anders?


Dit is een van die groot oorblywende raaisels van die heelal. Ek het 'n idee hieroor dat ons bekende vergelykings vir swaartekrag kan aflei, soos hieronder beskryf (dit is nie bewys nie, maar ek glo dat dit waarskynlik die geval sal wees). Ander mense het ook hieraan gedink, maar dit is nog nie die algemene siening nie. In werklikheid het iemand 'n referaat daaroor geskryf, wat hier bespreek word: http://www.angelfire.com/pq/spaceflow/part2.html

My gravitasie-idee (vereenvoudig):

Hierdie onlangse YouTube-video van ScienceClic English illustreer my idee eintlik baie goed:

Ek glo dat swaartekrag die vloei van die ruimte self in massa is. Per ruimte verwys ek na die drie dimensies van die ruimte wat ons in die heelal waarneem. Ek glo dat alle massa die ruimte rondom dit "absorbeer" en alles nader aan homself bring. Om dit te konseptualiseer, stel jou voor dat massa 'n stofsuier is, die lug suig en die stof in die lug rondom. Dit het die grootste uitwerking op die lug wat die naaste aan die vakuum is, en ek glo dat massa ook so met die ruimte optree. Aangesien die gekoppelde video Relativiteit verduidelik, is my idee miskien eintlik 'n verklaring van Relativiteit.

Verskeie dinge verklaar dit:

  1. Dit verklaar waarom voorwerpe met meer massa meer swaartekrag het (bv. Elke bietjie massa absorbeer 'n klein hoeveelheid ruimte, so ook swaartekrag). Hoe meer massa u het, hoe meer erns het u.

  2. Dit verklaar waarom swaartekrag sterk is naby 'n voorwerp (bv. Naby die aarde), en omgekeerd eweredig aan die vierkante afstand van die voorwerp afneem. As u dink dat 'n "sferiese golf" van die ruimte na binne beweeg, neem die oppervlakte van die sfeer toe in verhouding tot die vierkant van die afstand. Die effek versprei egter oor hierdie verhoogde oppervlakte, dus verminder dit met die vierkant van die afstand vanaf die voorwerp. 'N Redelik eenvoudige (maar 2D versus 3D) analogie is dat wanneer 'n klip in die water gegooi word, die rimpel eers sterk sal wees, naby die toegangspunt, en dan versprei die rimpel as dit uitbrei in die omliggende dam. 'N Goeie 3D-analogie is hoe klank (of lig) sferies uitbrei en flouer is hoe langer jy van die bron af is.

  3. Die wentelbaan van "binêre" stelsels, insluitend die dinamika tussen die aarde en die maan. Die aarde is massiewer as die maan en absorbeer meer ruimte as die maan. Daarom beweeg dit die maan redelik vinnig daarheen (maar die maan het genoeg momentum dat dit in 'n wentelbaan bly teenoor die aarde). Die maan trek egter ook na die aarde, dus val die aarde ook 'n bietjie na die maan toe. Weereens het die aarde genoeg momentum om nie 'in die maan te val' nie. Dit het meestal tot gevolg dat die maan om die aarde wentel, maar die aarde wentel ook 'effens' om die maan, wat as 'n effense wankel gesien kan word.

  4. Dit verklaar waarom groot massa voorwerpe en klein massa voorwerpe dieselfde beïnvloed word deur swaartekrag. Aangesien dit die ruimte is wat beweeg, sal die ruimte wat daar is, daarvolgens geskuif word. As dit 'n aambeeld is, sal dit net soos 'n veer beweeg word. Daarom (as dit nie ander effekte soos lugweerstand was nie), sou 'n veer dieselfde spoed as 'n aambeeld op die aarde val. In die praktyk maak lugweerstand die veer kleiner baie stadiger (maar herhaal die eksperiment op die maan, en hulle moet terselfdertyd tref omdat dit geen lug het nie).

  5. Dit verklaar selfs waarom dinge sonder massa (bv. Lig) ook deur swaartekrag beïnvloed word. Aangesien die ruimte self beweeg, beweeg lig daarmee saam. Dit verklaar gravitasie-lens, en waarom lig nie aan 'n swart gat kan ontsnap nie.

Tweede deel van my idee (meer spekulatief):

Ek glo ook dat antimaterie op die een of ander manier voortdurend ruimte in die heelal uitstoot. Stel u voor dat die omgekeerde in die video gebeur (byvoorbeeld as u dit agteruit kon speel). Ek glo dat wanneer materie en antimaterie gevorm word, dit op die een of ander manier "gekoppel" word sodat die ruimte wat deur materie geabsorbeer word deur die ooreenstemmende antimaterie deeltjie uitgegooi word. Dit sal antimateriale 'n 'negatiewe' swaartekrag-effek gee. Ek glo dat daar gelyke hoeveelhede materie en antimaterie in die heelal is, en dat die antimaterie in 'n diffuse wolk versprei is deur die heelal, waar materie nie voorkom nie. Ek glo dat dit donker energie verteenwoordig - die vinnige uitbreiding van die heelal.


Ek kan probeer om die tweede gedeelte van u aanvanklike vraag aan te spreek (* "Is dit 'n deeltjie, 'n golf, ...?") Einstein se teorie van algemene relatiwiteit stel dat massa en energie ruimtetyd buig. Ruimtyd vertel op sy beurt saak hoe om te beweeg (John Wheeler stel dit meer elegant).

Hierdie konsep verskil heeltemal van die teorieë van die ander drie fundamentele kragte (elektromagnetisme en die sterk en swak kernkragte). In hierdie kwantumteorieë word kragte bemiddel deur deeltjies wat maatbosone genoem word. Elektromagnetisme word deur fotone gedra, die sterk kernkrag deur gluone en die swak kernkrag deur W +, W- en Z-bosone. Daar is al vele pogings aangewend om 'n kwantumteorie van swaartekrag te vind - dit wil sê om kwantumbeginsels te gebruik om 'n veldteorie van swaartekrag te konstrueer. In hierdie teorieë sal swaartekrag wel bemiddel word deur 'n deeltjie, genaamd die graviton. Stringteorie is een voorbeeld van hierdie teorieë; die fisika-gemeenskap is verdeeld daaroor.

U het waarskynlik al die ander terme gehoor wat interessante begrippe bevat. A swaartekraggolf is in wese 'n rimpel in die tyd wat deur 'n voorwerp of stelsel van voorwerpe uitgestraal word. Daar is streng beperkings oor watter soort voorwerpe hierdie golwe kan uitstraal; binêre neutronsterre is 'n konsekwente voorbeeld. Hierdie golwe moet nie verwar word met die voorgenoemde hipotese gravitons; terwyl swaartekraggolwe energie dra, "bemiddel" hulle nie swaartekrag nie. Hulle moet ook nie verwar word met die onverwante swaartekraggolwe nie.

Die basiese siening in die fisika-gemeenskap is dus basies dat algemene relatiwiteit die beste beskrywing van swaartekrag is; op die oomblik word swaartekrag beskou as die buiging van ruimtetyd, dus is dit inderdaad 'iets heeltemal anders'. Baie teorieë oor kwantum-swaartekrag, insluitend tou-teorie, poog egter om deeltjies genaamd gravitons as kragdraende bosone te skep. As daar bewyse gevind word wat verband hou met hierdie teorieë, kan ons goed leer of gravitons bestaan ​​al dan nie. Nog iets oor golwe: Vanweë die kwantumbegrip van golfdeeltjie-dualiteit kan enige deeltjie beskryf word as 'n golf met 'n golffunksie. As swaartekrag dus deur 'n deeltjie gedra word, dan word dit ook deur 'n golf gedra!


Gedagtes van 'n planeet: So, soos, wat is swaartekrag?

U het waarskynlik botsende dinge oor swaartekrag gehoor. In die popkultuur word dit gelyktydig as triviaal eenvoudig en ongelooflik kompleks behandel. Ons leer op 'n jong ouderdom van Isaac Newton en sy appel en dit alles. Maar die werklike wiskunde raak ons ​​gewoonlik nie tot die fisikaklas nie.

Ons praat die heeltyd oor die "swaartekrag", maar u het miskien ook gehoor dat "swaartekrag 'n illusie is" of miskien iets in die nuus oor swaartekraggolwe gesien het.

Wat is swaartekrag? Is dit 'n krag of is dit iets anders?

Deel van hoekom Ek praat hieroor omdat mense my gereeld hierdie vrae oor swaartekrag vra, maar dit is ook 'n goeie beginpunt om te praat oor hoe wiskunde en wetenskap saamwerk om voorspellings oor die heelal te maak.

Swaartekrag is 'n waargenome verskynsel. Swaartekrag is ons term vir die ding waar voorwerpe met energie (meestal in die vorm van massa) oor tyd nader aan mekaar beweeg. Dit is nie 'n krag nie, en dit is 'n baie werklike ding wat ons sien, wat mense vir ewig gesien het.

Wat het Newton dan 'ontdek'?

Hy het al ontdek hoe om die beweging van alledaagse voorwerpe te voorspel deur die kragte daarop te definieer as die produk van hul massa en die waargenome versnelling - in fisiese terme het hy die verhouding reeds beskryf F = ma.

Newton het toe agtergekom dat swaartekrag gemodelleer kan word as 'n krag wat op elke voorwerp inwerk in verhouding tot die massa van ander voorwerpe: dat as jy voorgee dat die swaartekrag eintlik 'n krag is wat dinge saamtrek, dan verklaar dit die pad van 'n appel wat van boom of 'n pyl uit 'n boog of waarom die maan om die aarde wentel.

In wese het hy ontdek dat jy wiskunde kan gebruik om die gevolge van swaartekrag te voorspel as jy dit soos 'n krag behandel.

Is swaartekrag dan tog 'n krag? Nope. Dis die waargenome verskynsel dat energieke voorwerpe na mekaar beweeg. Die meeste van die gevolge daarvan kan voorspel word deur dit as 'n krag te behandel, maar dit beteken nie dat dit nie is 'n krag.

Waarom praat fisici dan oor "die swaartekrag"?

Die kort antwoord is dat hulle lui is.

Die lang antwoord is dat fisika die wetenskap is om wiskunde te gebruik om materie en die beweging daarvan deur ruimte en tyd te verklaar. In daardie konteks word swaartekrag meestal beskryf as 'n krag wat voorwerpe saamtrek. Aangesien dit is hoe ons dit in wiskunde gebruik, praat fisici daaroor.

As u byvoorbeeld 'n brug wil ontwerp, moet u 'n klomp dinge soos druk, inwendige spanning, windskuif en swaartekrag balanseer. Jy gee nie regtig om oor die konsep van swaartekrag, gee jy om of jou brug gaan val of nie, en om swaartekrag as 'n krag te hanteer, sal dit vir jou beantwoord.

Toe kom Einstein saam. Einstein het 'n akkurater manier uitgevind om die gevolge van swaartekrag te voorspel. Newton se model (om swaartekrag as 'n krag te behandel) is regtig goed die meeste dinge, maar spreek nie korrekte voorspellings op groot skale of naby baie massiewe voorwerpe nie. Einstein se gereedskap, wat hy gesamentlik Algemene Relatiwiteit noem, is beter om daardie dinge te voorspel.

'N Eenvoudige manier om Algemene Relatiwiteit te beskryf, is dat energie die ruimte (en tyd) verdraai op 'n manier wat veroorsaak dat andersins reguit paaie deur die ruimtetyd gebuig lyk. Die beweging van voorwerpe wat langs daardie geboë paaie beweeg, word beskou as swaartekrag.

Is dit ingewikkelder? Verseker. Eerlik gesê, dit is die spul nagmerries. Maar as dit gaan om voorspellings, word die doeltreffendheid daarvan slegs oortref deur een ander wetenskaplike teorie - die kwantumveldteorie, wat dit fundamenteel stem nie saam nie. Oeps!

Beteken dit dat Newton verkeerd was? Nee nie regtig nie. Sy eenvoudiger model is slegter om die relatiewe bewegings van sterrestelsels en planete te voorspel, maar dit beteken nie dat dit verkeerd is nie. As dit met Einstein beter is om dinge te voorspel, beteken dit dan dat swaartekrag regtig die kromtrekking van die ruimte is as gevolg van energie?

Nee, swaartekrag is die waargenome verskynsel dat voorwerpe met energie na mekaar beweeg. Onthou jy?

Ons "ontdek" nie die fisika van die Heelal nie, ons bou gereedskap om ons te help om dit te voorspel en in hierdie geval wiskunde uit te dink wat baie akkuraat is om dit te voorspel. En dit is nogal hoe dit alles werk.

As ons die gedrag van gasse voorspel, behandel ons dit dikwels as 'n versameling geïdealiseerde, puntagtige deeltjies sonder intermolekulêre aantrekking. Dit is eintlik nie, maar die resultate werk redelik goed as u 'n opblaasballon of 'n stoomenjin wil beskryf. In die kwantumveldteorie behandel ons die heelal as bedekte kwantumvelde, met elke deeltjie as 'n opgewekte toestand in sy onderliggende veld. Beteken dit die heelal? is oorvleuelende kwantumvelde? Wel, nee. Die Heelal is die Heelal, maar dit is effektief om dit so te modelleer.

Dit is baie nuttig om swaartekrag as 'n krag voor te stel dit werk. En dit kan u help om allerhande werklike probleme op te los. U kan 'n brug bou wat die swaartekrag ignoreer, maar wees nie verbaas as dit val nie.


Wat is swaartekrag?

Ons weet almal wat swaartekrag is en dit is wat ons op die aarde hou. Dit is die krag wat appel langs die boom laat val. Maar wat is die definisie van swaartekrag in fisika? Dit is een van die fundamentele interaksies in die heelal. Fundamentele interaksies in fisika is vier heeltemal verskillende aard-interaksies tussen elementêre deeltjies en liggame wat hulle bou. Baie pogings in die moderne fisika is gefokus op die vind van 'n gemeenskaplike verenigde teorie wat alle interaksies sal verenig. Tot dusver word so 'n teorie nie gevind nie. Hier is hulle:

  • Gravitasie-interaksie
  • Elektromagnetiese interaksie
  • Sterk kerninteraksie
  • Swak kerninteraksie

Die gravitasie-interaksie, of swaartekrag, word uitgedruk in die bestaan ​​van 'n krag van wedersydse aantrekkingskrag tussen alle materiële voorwerpe wat massa het.

Die eerste wiskundige model wat swaartekrag beskryf, geskep deur Sir Isaac Newton en is uiteengesit in die gepubliseerde werk in 1687. Wiskundige beginsels van die natuurfilosofie (Philosophia Naturalis Principia Mathematica). Die belangrikste implikasies van hierdie werk is die bewegingswette van Newton en die wet van Newton. van universele aantrekkingskrag (swaartekrag).

Newton aanvaar die bestaan ​​van 'n krag van & # 8220universal gravitational pull. & # 8221 Sy wet van swaartekrag lui: & # 8220 Die sterkte waarmee die twee materiële punte mekaar aantrek, is direk eweredig aan die produk van hul massas en omgekeerd eweredig aan die vierkant van die afstand tussen hulle. & # 8220 Hierdie vergelyking was egter nie so akkuraat toe dit geïmplementeer is vir die wentelbaan van Mercurius wat probeer om presies te bereken wanneer die planeet na die son sal vervoer nie. Wetenskaplikes erken selfs die bestaan ​​van 'n ander planeet wat Mercurius beïnvloed om hul berekeninge aan te pas.

Wat is swaartekrag in die fisika deesdae?

Gelukkig bied Einstein egter 'n heel ander siening van die swaartekrag en die algemene relatiwiteitsteorie keer al ons idees daaroor. Die raaisel is opgelos deur sy teorie oor Mercurius toe te pas. Volgens die algemene relatiwiteitsteorie in plaas van 'n mate van krag, word die effek van Gravity gesien as 'n vervorming van die ruimtetyd. Die grondslag van algemene relatiwiteit lê die beginsel van ekwivalensie wat vrye val met traagheidsbeweging verenig.

In 'n eenvoudige taal vertaal, skep elke liggaam iets soos 'n deuk in ruimtetyd wat alle ander bewegende liggame moet volg om daarin te val. En so vir elke liggaam in die heelal, van die massiewe swart gat tot die kleinste stofkol. Daarom val die maan op die aarde, die aarde val op die son en die sonnestelsel val in die middel van die melkweg. En as ons kon neerkyk op die hele prentjie, die hele veld van die Heelal, sou dit lyk soos 'n eindelose bergreeks, gevorm deur die grootste beeldhouer en haar majesteit swaartekrag.

Ek hou regtig van die Gravity-soort wat daarop val. En dit is omdat ek oral waar ek draai, 'n wonderlike wêreld sien wat daaruit geskilder is. Alle pragtige landskap word meesterlik deur Gravity geskilder. Snags as ek na die sterrehemel kyk, sien ek 'n ongelooflike mooi prentjie, en die dryfkrag van die geverfde kwas is weer die Swaartekrag. Dit is 'n groot kunstenaar en die skepper van die wêreld. Dit is omdat dit die enigste krag in die heelal is wat deur die groot afstand in die ruimte kan beweeg en die stof verbind om planete, mane, sterre en sterrestelsels te skep.


Is swaartekrag regtig? Die wetenskap is op die punt om uit te vind

Die verdraaiing van ruimtetyd, in die Algemene Relativistiese prentjie, deur swaartekragmassas is wat. [+] veroorsaak die swaartekrag. Daar word aanvaar, maar nie eksperimenteel geverifieer nie, dat antimateriale massas dieselfde sal optree as materiemassas in 'n swaartekragveld.

Een van die verstommendste feite oor die wetenskap is hoe die natuurwette universeel toepaslik is. Elke deeltjie volg dieselfde reëls, ervaar dieselfde kragte en sien dieselfde fundamentele konstantes, ongeag waar of wanneer dit bestaan. Gravitasioneel ervaar elke enkele entiteit in die heelal, afhangende van hoe u daarna kyk, dieselfde gravitasieversnelling of dieselfde kromming van die ruimtetyd, ongeag watter eienskappe dit besit.

Ten minste is dit hoe dinge in die teorie is. In die praktyk is sommige dinge moeilik meetbaar. Fotone en normale, stabiele deeltjies val albei soos verwag in 'n gravitasieveld, met die Aarde wat veroorsaak dat enige massiewe deeltjie teen 9.8 m / s 2 na sy middelpunt versnel. Ondanks ons beste pogings, het ons egter nog nooit die swaartekragversnelling van antimateriale gemeet nie. Dit moet presies op dieselfde manier versnel, maar totdat ons dit meet, kan ons nie weet nie. Een eksperiment is om die saak eens en vir altyd te probeer beslis. Afhangend van wat dit vind, is dit dalk die sleutel tot 'n wetenskaplike en tegnologiese rewolusie.

Bane van antiwaterstofatome uit die ALPHA-eksperiment. Ons kan hulle tot 20 stabiel hou. [+] minute op 'n slag is die volgende logiese stap om te meet hoe hulle in 'n gravitasieveld optree.

Chukman So / Universiteit van Kalifornië, Berkeley

U besef dit miskien nie, maar daar is twee verskillende maniere om oor massa te dink. Aan die een kant is daar die massa wat versnel wanneer u 'n krag daarop uitoefen: die m in Newton se beroemde vergelyking, F = ma. Dit is dieselfde as die m in Einstein s'n E = mc 2 , wat jou vertel hoeveel energie jy nodig het om 'n deeltjie (of antipartikel) te skep en hoeveel energie jy kry as jy dit vernietig.

Maar daar is nog 'n massa daar buite: swaartekragmassa. Dit is die massa, m, wat in die vergelyking vir gewig op die aarde se oppervlak voorkom (W = mg), of in die gravitasiewet van Newton, F = GmM / r 2 . Vir normale aangeleenthede weet ons dat hierdie twee massas - traagheidsmassa en swaartekragmassa - gelyk moet wees aan iets soos 1 deel in 100 miljard, danksy eksperimentele beperkings van 'n opstelling wat meer as 100 jaar gelede deur Loránd Eötvös ontwerp is.

Newton se wet van universele gravitasie (L) en Coulomb se wet vir elektrostatika (R) het amper. [+] identiese vorms. As die 'm' in die gravitasiekrag 'n negatiewe teken vir antimaterie kry, behoort komende eksperimente dit te openbaar.

Dennis Nilsson / RJB1 / E. Siegel

Vir antimateriale kon ons dit egter nog nooit meet nie. Ons het nie-gravitasiekragte op antimaterie toegepas en gesien hoe dit versnel, en ons het antimaterie ook geskep en vernietig. Ons is seker hoe die traagheidsmassa daarvan optree, en dit is presies dieselfde as die traagheidsmassa van normale materie. Albei F = ma en E = mc 2 werk net dieselfde vir antimateriale as vir normale materie.

Maar as ons wil weet hoe antimateriaal swaartekrag optree, kan ons nie net afgaan op wat ons teoreties verwag om dit te meet nie. Gelukkig is daar nou 'n eksperiment wat ontwerp is om presies dit te doen: die ALPHA-eksperiment by CERN.

Die ALPHA-samewerking kom die naaste van enige eksperiment om die gedrag van neutraal te meet. [+] antimaterie in swaartekragveld. Met die komende ALPHA-g-detector weet ons miskien uiteindelik die antwoord.

Een van die groot vordering wat onlangs geneem is, is die skepping van nie net deeltjies antimaterie nie, maar ook neutrale, stabiele gebonde toestande daarvan. Anti-protone en positrone (anti-elektrone) kan geskep word, vertraag en gedwing word om met mekaar te kommunikeer, waar dit neutrale anti-waterstof vorm. Deur 'n kombinasie van elektriese en magnetiese velde te gebruik, kan ons hierdie anti-atome beperk en dit stabiel hou, weg van die saak wat hulle kan vernietig.

Ons het hulle ongeveer 20 minute op 'n slag stabiel gehou, wat die mikrosekonde tydskale oortref wat onstabiele, fundamentele deeltjies oorleef. Ons het hulle met fotone getref en ontdek dat hulle dieselfde emissie- en absorpsiespektrum as atome het. In elke opsig wat belangrik is, het ons vasgestel dat die antimateriale se eienskappe presies is soos standaardfisika voorspel.

Die ALPHA-g-detektor, gebou by die Kanada se deeltjiesversneller-aanleg, TRIUMF, is die eerste daarvan. [+] soort wat ontwerp is om die effek van swaartekrag op antimateriale te meet. As dit vertikaal gerig is, moet dit kan meet in watter rigting antimaterie val en in watter grootte.

Behalwe natuurlik swaartekrag. Die nuwe ALPHA-g-detektor, wat in die TRIUMF-fabriek in Kanada gebou is en vroeër vanjaar na CERN gestuur is, sou die grense vir die swaartekragversnelling van antimateriale tot op die kritieke drempel moes verbeter. Versnel antimateria, in die teenwoordigheid van die swaartekragveld op die aardoppervlak, op +9,8 m / s 2 (af), by -9,8 m / s 2 (op), by 0 m / s 2 (geen gravitasieversnelling by alles), of 'n ander waarde?

Vanuit 'n teoretiese en 'n toepassingsperspektief, sal enige ander resultaat as die verwagte +9,8 m / s 2 absoluut revolusionêr wees.

As daar een of ander soort materie was wat negatiewe gravitasielading gehad het, sou dit afgestoot word deur. [+] die saak en energie waarvan ons bewus is.

Muu-karhu van Wikimedia Commons

Die antimaterie-eweknie van elke stofdeeltjie moet:

  • dieselfde massa,
  • dieselfde versnelling in 'n swaartekragveld,
  • die teenoorgestelde elektriese lading,
  • die teenoorgestelde draai,
  • dieselfde magnetiese eienskappe,
  • moet op dieselfde manier saambind tot atome, molekules en groter strukture,
  • en moet dieselfde spektrum positron-oorgange hê in verskillende konfigurasies.

Sommige hiervan is al lank gemeet: die traagheidsmassa, die elektriese lading, die draai en die magnetiese eienskappe van die antimaterie is bekend. Die bindings- en oorgangseienskappe daarvan is tydens die ALPHA-eksperiment deur ander detektors gemeet en stem ooreen met wat deeltjiefisika voorspel.

Maar as die gravitasieversnelling negatief in plaas van positief is, sal dit die wêreld letterlik onderstebo laat draai.

Die moontlikheid om kunsmatige swaartekrag te hê, is tergend, maar dit is afhanklik van die bestaan. [+] van negatiewe swaartekragmassa. Antimaterie is miskien die massa, maar ons weet dit nog nie eksperimenteel nie.

Tans bestaan ​​daar nie iets soos 'n swaartekraggeleier nie. Op 'n elektriese geleier leef gratis ladings op die oppervlak en kan hulle rondbeweeg en hulself herverdeel in reaksie op enige ander ladings. As u 'n elektriese lading buite 'n elektriese geleier het, sal die binnekant van die geleier teen daardie elektriese bron beskerm word.

Maar daar is geen manier om jouself te beskerm teen die swaartekrag nie. Daar is ook geen manier om 'n eenvormige swaartekragveld in 'n ruimte op te stel nie, soos u ook tussen die parallelle plate van 'n elektriese kondensator kan doen. Die rede? Want in teenstelling met die elektriese krag, wat deur positiewe en negatiewe ladings gegenereer word, is daar net een soort gravitasielading, en dit is massa-en-energie. Die gravitasiekrag is altyd aantreklik, en daar is eenvoudig geen manier om dit te omseil nie.

Skematiese diagram van 'n kondensator, waar twee parallelle geleidingsplate gelyk en teenoorgestelde is. [+] laai, wat 'n eenvormige elektriese veld tussen hulle skep. Hierdie konfigurasie is onmoontlik vir swaartekrag, tensy daar een of ander vorm van negatiewe swaartekragmassa is.

Wikimedia Commons-gebruiker Papa November

Maar as u 'n negatiewe swaartekragmassa het, verander dit alles. As die antimateriaal antigravitasie-effekte is, val op in plaas van af, dan sien die swaartekrag dit asof dit van antimassa of anti-energie is. Volgens die wette van die fisika wat ons tans verstaan, bestaan ​​daar nie hoeveelhede soos antimassa of anti-energie nie. Ons kan hulle voorstel en praat oor hoe hulle sou optree, maar ons verwag dat antimateriale normale massa en normale energie sal hê as dit by swaartekrag kom.

As daar egter teenmassa bestaan, sou 'n klomp groot tegnologiese vooruitgang, wat generasies deur wetenskapfiksieskrywers voorgestel het, skielik fisies moontlik word.

Die Virtual IronBird-instrument vir die CAM (Centrifuge Accommodation Module) is een manier om te skep. [+] kunsmatige swaartekrag, maar benodig baie energie en laat slegs 'n baie spesifieke, middagsoekende soort krag toe. Ware kunsmatige swaartekrag sou iets vereis om met negatiewe massa op te tree.

Ons kan 'n swaartekraggeleier bou en ons teen die gravitasiekrag beskerm.

Ons kan 'n gravitasiekondensator in die ruimte opstel en 'n eenvormige kunsmatige swaartekragveld skep.

Ons kan selfs skeefaandrywing skep, aangesien ons die vermoë sou hê om die ruimtetyd te vervorm presies soos 'n wiskundige oplossing vir Algemene Relatiwiteit, wat Miguel Alcubierre in 1994 ontdek het, vereis.

Die Alcubierre-oplossing vir algemene relatiwiteit, wat beweging soortgelyk aan skering aandryf. Hierdie oplossing. [+] benodig negatiewe swaartekragmassa, wat presies die antimaterie kan wees.

Wikimedia Commons-gebruiker AllenMcC

Dit is 'n ongelooflike moontlikheid, wat prakties deur alle teoretiese fisici as onwaarskynlik beskou word. Dit maak nie saak hoe woes of mak u teorieë is nie, u moet hulle absoluut slegs met eksperimentele gegewens konfronteer deur die heelal te meet en dit op die proef te stel, u kan ooit akkuraat bepaal hoe die natuurwette werk.

Totdat ons die swaartekragversnelling van antimateriale meet tot die presisie wat nodig is om te bepaal of dit op of af val, moet ons onsself oop hou vir die moontlikheid dat die natuur nie kan optree soos ons verwag nie. Die ekwivalensiebeginsel is miskien nie waar vir antimaterie nie, maar in werklikheid 100% anti-waar. Maar as dit die geval is, sal 'n hele nuwe wêreld van moontlikhede ontsluit word. Ons kan die huidige limiete verander wat mense in die heelal kan skep. En ons sal die antwoord binne 'n paar jaar leer deur middel van die eenvoudigste eksperimente: om 'n anti-atoom in 'n swaartekragveld te plaas en te kyk in watter rigting dit val.


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Wat is swaartekrag regtig? - Sterrekunde

Wanneer ons met fisika te doen het en probeer om die werking van swaartekrag te verweef, moet ons ons idee van swaartekrag uitbrei om nie net die verskynsel van val te omvat nie, maar ook 'n begrip van die oorsaak, bron, snelheid van beweging (beweging) en die verband daarvan. met buite-voorwerpe en die omgewing.

Sir Isaac Newton is die histories bekende Britse wetenskaplike en wiskundige wat wette geformuleer het rakende beweging en swaartekrag.

Newton het bepaal dat swaartekrag een van die universele kragte van die natuur is. Hy het ontdek dat dit 'n krag van aantrekkingskrag geassosieer met alle materie. Hierdie krag is afhanklik van die massa van die onderskeie voorwerpe.

Deur ons onopgeleide oog alleen kan ons nie swaartekrag aan die werk sien nie. Dit is eers wanneer een van die voorwerpe geweldig groot is (soos die Aarde) dat ons getuig van sy swaartekrag.

Met behulp van wiskundige vergelykings het Newton sy Wet op Universele Gravitasie geformuleer, wat lui:

"Swaartekrag is die sterkste tussen twee baie massiewe voorwerpe, en word baie swakker namate hierdie voorwerpe verder uitmekaar kom."

B. Ontsnap snelheid

Met sy oorspronklike formule het Newton die innerlike werking van die wet omlyn, soos waarna hy verwys het ontsnap snelheid, die snelheid wat 'n voorwerp moet bereik om aan die swaartekrag van 'n ander voorwerp te ontsnap. Die ontsnappingssnelheid van 'n voorwerp kan gevind word deur die Wet op Gravitasie van Newton te gebruik.

Oorweeg vir 'n oomblik swart gate. Wanneer ons die konsep van ontsnaptoerusting op hierdie boeiende strukture toepas, kom ons agter dat die ontsnappingssnelheid gelyk is aan die snelheid van die lig omdat dit so baie klein en dig is. Daarom ontsnap slegs lig aan die donker afgrond van 'n swart gat.

C. Krag van swaartekrag

Die term swaartekrag verwys na die trek tussen voorwerpe en aarde. As mense ervaar ons hierdie krag, dit is wat ons voete stewig op die grond geplant hou in plaas van in die ruimte rond te sweef. As ons opwaarts spring, geld dieselfde krag. As ons opstaan, vertraag die swaartekrag ons, maar versnel ons weer as ons voete na die grond terugkom. Hierdie krag word versnelling genoem. Ons noem hierdie verskynsel "versnelling van swaartekrag (g)." Dit is die versnelling wat 'n voorwerp ervaar as daar geen ander kragte van buite is wat daarop inwerk nie.

Dit is interessant dat die versnellingswaarde vir alle voorwerpe presies dieselfde is, ongeag hul individuele massa.

Die studie van wrywing staan ​​bekend as tribologie.

Wrywing is die neweproduk van atoom- en molekulêre kragte wat in wisselwerking tree wanneer oppervlaktes met mekaar in aanraking kom. Wrywing kom byvoorbeeld voor wanneer u met u kaal voete op die mat loop of deur 'n vloeibare medium (water, lug, ensovoorts).

Wrywing word beskou as 'n weerstandstipe krag wat op liggame inwerk wat geneig is om beweging te weerstaan ​​en (of) te demp.

In wese bestaan ​​daar twee soorte wrywing:

1. Die Statiese krag van wrywing (fs). Die wrywingskrag tussen twee voorwerpe wanneer daar is geen beweging.

2. Die Kinetiese krag van wrywing (fk). Die wrywingskrag tussen twee voorwerpe wanneer daar is beweging.

Wrywing word gewoonlik onderskei as óf statiese wrywing (die teenoorgestelde wrywingskrag as liggaam gaan van rus na beweging) of kinetiese wrywing (die wrywingskrag wat geneig is om 'n liggaam in beweging te vertraag). Ter vergelyking is statiese wrywing groter as kinetiese wrywing.

Die krag wat toegeskryf word aan kinetiese wrywing is geneig om eweredig te wees met die toegepaste krag. Daarom word 'n "koëffisiënt van kinetiese fiksie" gedefinieer as die verhouding van wrywingskrag tot die normale krag op die liggaam.

In kinetiese wrywing is daar onderafdelings van wrywing: gly, rol en vloeibare wrywing. Weereens, as die voorwerp roerloos bly, is dit staties.

Glywrywing. Dit vind plaas wanneer twee soliede voorwerpe met mekaar in aanraking kom en 'n buitekrag word toegepas wat een van die voorwerpe in die ander skuif. Vergelykings wat dui op glywrywing word uitgedruk met F as die krag wat weerstand teen die voorwerp uitoefen en Fr as die krag van die wrywing.

Gly wrywing. Oorsake

Die oorsake van glywrywing kan 'n rowwe oppervlak, 'n molekulêre aantrekkingskrag, hechting tussen die materiale of vervormingsweerstand insluit (soos die geval is met sagte materiale).

As 'n krag toegepas word, alhoewel dit nie genoeg is om die statiese wrywingskrag in te haal nie, sal die wiel begin rol. As die krag groter is as die statiese weerstand, sal die wiel uiteindelik gly of draai. En hoewel dit nog steeds sal rol, sal dit teen 'n laer snelheid doen.

'N Demonstrasie van hierdie konsep kan gesien word deur 'n motor te laat versnel op 'n gladde, nat lappie beton. As u die versnellerpedaal te hard druk, dien dit net om die wiele te laat draai, eerder as om die motor vorentoe te beweeg, maal dit net op sy plek.

Once the wheel (think automobile) is set in motion (rolling), friction occurs at the point of contact with the other surface (in our example this would be the pavement), slowing the motion of the wheel. Typically, rolling friction is much less powerful than sliding friction. This is why a wheel can roll for some distance before slowing down and coming to a complete halt.

Rolling Friction. Causes

Similar to those of sliding friction, the causes of rolling friction include roughness of the surface, molecular attraction or adhesion between the materials, and deformation resistance as is the case with soft materials.

E. Fluid Friction.

When a solid object is in contact with a fluid (regardless of whether it is a liquid or a gas) and a force exerts pressure on either the object or the fluid, the result is a friction force that defies the motion. Examples of fluid friction include water flowing through a pipe, an airplane flying through the clouds or atmosphere, and oil lubricating an automobile engine parts.

F. Static and Kinetic Friction

If the viscosity (thickness) of the fluid is substantial, there may be zero movement on account of the presence of static friction. An example is trying to push oil up through a drill pump. At first, a great deal of pressure may be needed to cut through the static friction so that the oil can gush forth.

Going from static to kinetic friction, once the oil begins to move through the pump, the resistance shifts gears. Even though the oil may now be flowing, it will still be traveling at a slower speed than a fluid that has a low viscosity, like water.

Nota: It is also possible for fluid friction to occur in cases where one fluid comes into contact with another fluid. This type of scenario is usually categorized as part of the field of Fluid Dynamics.

Causes of fluid friction include the effects of turbulence caused from surface roughness and deformities, molecular attraction, or adhesion between the materials, and deformation that exerts resistance against the fluid.


Sir Isaac Newton

Isaac Newton was born in England in 1643. As a young man he went to Trinity College in Cambridge, enrolling first as a student and eventually staying on as a fellow. During this period he developed the first versions of his three laws of motion, including the law of gravity. During his career, he also made significant advances in the field of optics and the understanding of centrifugal force. He eventually became the first English scientist to be knighted for his work.


Is gravity not actually a force? Forcing theory to meet experiments

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How are controversial ideas handled by modern science? A common charge leveled against science (generally by those who are unhappy with its conclusions) is that the only way to get funding or continue your research is by going along with the current theories and not rocking the boat. For those who spend their careers in science, this is laughable—it is those who successfully rock the boat who are the most successful. In this article, we are going to look at a manuscript that purports to overturn hundreds of years of accepted ideas about gravity, and use it as an illustration of how controversial ideas are dealt with in modern physics.

It was Isaac Newton who first proposed a universal law of gravitation, where every massive body in the universe was attracted to every other one. This simple law proved extremely powerful, able to explain the orbits of planets and the reason the apocryphal apple fell on his head. However, Newton was never able to explain why gravity worked or what exactly it was. Two hundred plus years later, Albert Einstein was able to offer a more complete description of gravity—one where Newton's laws are a limited case. According to Einstein, gravity was due to the warpage of spacetime by mass and energy all objects followed straight paths, just on curved spaces.

With the advent of quantum theory over the past 100 years, scientists have been able to develop an elegant mathematical framework capable of uniting three of the four fundamental forces that are thought to exist in the universe. The fourth, gravity, still remains the fly in the ointment, and has resisted unification to this point. Early last year, Dutch theoretical physicist Erik Verlinde published a manuscript to the arXiv that purports to explain why science cannot reconcile all four fundamental forces. According to him, it is simple: "gravity doesn’t exist."

Some background reading

Before we dive into this seemingly unphysical statement, we need to take a detour to discuss some of the ideas from modern physics that form the basis of Dr. Verlinde's argument: black hole thermodynamics and the holographic principle. Black hole thermodynamics was worked on extensively in the 1970s. It's needed in order to reconcile the second law of thermodynamics with the idea of a black hole event horizon. To do this, one has to admit that a black hole must have finite, non-zero entropy. If a black hole has zero entropy, then throwing mass into a black hole would violate the second law of thermodynamics, as the sum total entropy of the universe would decrease by the amount of entropy contained within the mass.

This also demands that, oddly, black holes cannot be purely black. If something has a non-zero entropy, then it must also have a non-zero temperature. This temperature is the temperature of the Hawking radiation that is given off due to the quantum nature of the black hole itself. A simple way to imagine Hawking radiation involves considering the particle-antiparticle pairs that spontaneously form the vacuum fluctuations. If one forms near the event horizon, it can fall in, never to be seen again, while its mate flies off into the Universe. To a faraway observer, the black hole just emitted a particle (even trippier is the fact that the particle that fell in must have had negative energy, and decreased the total energy of the black hole—something that could cause the black hole to evaporate over time).

Leading us further down the (black) rabbit hole are other results of Stephen Hawking's calculations, which fixed the maximum entropy that a black hole can have. Since that's a (quasi) measurement of how much information can be stored by an object, a black hole represents the most informationally dense object possible in the Universe. Surprisingly, the maximum entropy a black hole can obtain is exactly Planck's constant times one quarter of its area in Planck lengths—not its volume, an important distinction. This result implies that every bit of information the black hole can contain (as an Infosphere) is described entirely by its surface, the event horizon.

An extension to this line of surface-focused thinking came in the 1990s, when Gerardus 't Hooft, and later Leonard Susskind, postulated that the universe is a form of a hologram, a lower dimensional object that looks like a higher dimensional one (think of the two dimensional hologram images that look three dimensional). The holographic principle says that all space and time contained within an N dimensional body is emergent and can be described by a completely separate set of physics on the N-1 dimensional surface of the body.

This is one of those mind-bending ideas that float around and form the basis of a not-insignificant portion of modern physics, so I'll try and give a simple example. Imagine the entire Universe is a beach ball, and all physics within it—space, time, matter, energy—is described by the ideal gas law. The holographic principle then states that the entirety of the Universe (the inside of the beach ball) can also be described by a different set of equations that describe only the surface of the ball, the vinyl part itself as an example, maybe a set of equations linking the surface tension to the area of the ball.

There's a corollary to this (one that will be heavily relied on in a minute): all the information about the Universe (in this case the beach ball) is encoded on the two dimensional surface of the ball. Another analogy I have seen used to describe this is that of a soup can: everything you could know about what is in the can of soup is printed on its label.

Tying this back to the black holes we started with: the holographic principle suggests that everything we could want to know about the interior of a black hole is encoded in some manner on the surface of its event horizon. Since we can never recover information from beyond the veil of the event horizon, everything that can be known about a black hole, and everything that has ever fallen into it, must be represented on the event horizon itself. In fact, in some variants of string theory, this concept resolves the black hole information paradox.

This idea may sound completely abstract (and it is), but it has turned out to be remarkably useful, because it has produced what is called the AdS/CFT correspondence. This uses the holographic principle to show a direct correspondence between problems in what is known as Anti-deSitter space, where gravity is present (a cosmological way of describing the Universe) and problems in conformal field theory in a lower dimensional space where gravity does not exist (used heavily in quantum mechanics). Problems not solvable in one regime (cosmology, the AdS portion) have an equivalent problem that may be trivially solvable in the other (quantum field theory, the CFT portion).

A mind-bending proposal

Dr. Verlinde's proposition is not entirely unique. Others have argued that gravity, instead of being a fundamental force of the Universe, is instead an emergent phenomenon. A good deal of this thinking comes from the fact that the equations that describe gravity (in the Newtonian limit, at least) are mathematically similar to those that describe other emergent phenomena, such as fluid mechanics or thermodynamics. Where Dr. Verlinde goes the next step forward is by arguing for a definite mechanism behind gravity: differences in entropy.

In his freely available manuscript, entitled "On the Origin of Gravity and the Laws of Newton,"—the title seemingly paying homage to Einstein's famous paper whereby special relativity was laid out—Verlinde sets out his case for why gravity is, as he terms it, an "entropic force." The manuscript uses a combination of the holographic principle and black hole thermodynamics to (re)derive the basic equations of motion that Newton presented over 300 years prior.

Verlinde makes extensive use of the holographic principle in his derivations. He works with a thought experiment that assumes one has a holographic screen—one where all the information about what is contained inside of it is encoded as bits on its surface—and asks how it would interact with matter or energy that is being held net outside of it.

To show how Newton's equations of universal gravitation are derived, Verlinde begins with the difference in entropy between a mass M and a spherical holographic screen with entropy S—the information encoded on the screen would describe the emergent space inside, which would be "viewed" as equivalent to a mass M at its center. The attractive force between the the mass and the screen—what we would commonly call gravity—becomes, as Verlinde describes it, an entropic force due to the different informational densities between the two regions.

Not being content to leave it there, Verlinde goes further and rederives Newton's famous second law, F=ma (fun historical note: F=ma appears exactly zero times in Newton's famous Principia). Through that derivation, Verlinde is able to associate acceleration with an entropy gradient. According to his work, a particle at rest will stay at rest because there is no entropy gradient around it. This allows him to identify Newton's potential—the negative of the gradient, which is the acceleration a particle feels—as a potential that "keeps track of the depletion of the entropy per bit."

With such a description, extending the idea further becomes feasible. The entropic potential previously identified is shown to follow the common Poisson equation that describes the distribution of matter about a system. So he concludes that, if temperature and informational density on the holographic screen are chosen properly, then the laws of gravity fall out of this theory in a straightforward fashion.

Up to this point in the manuscript, everything Verlinde has derived applies to non-relativistic cases. How well does such a radical departure hold up when viewed through the lens of relativity theory? Here, Verlinde starts with the general relativistic description of Newton's potential. He then goes on to derive the force required to hold a particle a fixed distance away from a holographic screen, and again is able to derive the commonly accepted equation with force now described by a difference in entropy between the point and the screen. Furthermore, the manuscript lays out a path—but does not explicitly follow it—for one to rederive the full set of Einstein's field equations that form the cornerstone of general relativity using the fact that gravity, in Verlinde's work, is an "entropic force."

The paper is clearly unconventional, but it provides a compelling argument, and backs it up with actual work. Despite the highly controversial ideas it puts forth and the fact that it has not gone through peer review, it has caused some people in the scientific community to sit up and take notice.

Clearly, one paper making extraordinary claims will not be taken as fact until others can replicate the work, or in the case of a theoretical paper such as this, verify it with experimental evidence. A paper published in a recent edition of Physical Review D has attempted to do just that.

Not so fast

Dr. Archil Kobakhidze, a research fellow in theoretical particle physics at the University of Melbourne, points to recent results that may undermine Verlinde's ideas. Kobakhidze acknowledges that Verlinde's work successfully reproduces gravity on the Newtonian scale, and possibly in the more general relativistic sense, but it must also work at the quantum level as well, or it's not going to change modern physics.

Kobakhidze attempts to apply Verlinde's ideas to see if they are in agreement with the results from experiments on ultra-cold neutrons falling in the Earth's gravitational field. Solving the conventional quantum mechanical equations that describe this system give results that are in good agreement with the experiment. Verlinde's paper does not fully explain how to work with microscopic systems in his modified view of gravity, but according to Kobakhidze, enough ideas are present to work it out as homework.

Kobakhidze uses Verlinde's approach to re-derive the wave equation that will describe the energy levels of neutrons falling in Earth's gravitational well. What he finds is that, in contrast to the more conventional equation, there are two extra terms now present. One would appear to account for the relativistic rest energy of the neutron the other is a form of an extreme suppression of certain parts of the neutron's wavefunction. Both of these additions result in problems for Verlinde's theory.

The first extra term, the relativistic rest energy, would manifest itself as a constant shift in the neutron's energy states (height above the bottom of the well)—this is not seen at all in the experiments. According to Kobakhidze, though, it is the second extra term that really throws a wrench into entropic gravity. The second term, if correct, would significantly change the dynamics of the experiment, essentially causing neutrons to fall through the small hole in the bottom of the potential well. There's no sign of this happening in any meaningful way in the experiment. Thus, Kobakhidze concludes, "we are driven to the conclusion that gravity is not an entropic force."

This is how science works. Ideas are proposed, they are backed up, they are shot down. Over time, it would not surprise me to see Verlinde defend his work. Perhaps Kobakhidze's derivation and its extension to the microscopic case is incorrect. Perhaps Verlinde will revisit his original work to revise how microscopic cases should be handled. Whatever happens, science will move on time, further arguments, and experiments will be the ultimate arbiter of which drastically different view of reality is correct.


What is the quantum theory of gravity?

To answer this question, one must first understand how it came to be. When it was discovered in the early twentieth century that Newtonian physics, although it had stood unchallenged for hundreds of years, failed to answer basic questions about time and space, such as 'Is the universe infinite?' or 'Is time eternal?', a new basis for physics was needed. This lead to the development of Quantum Theory by Bohr, Schr'dinger and Heisenberg and Relativity Theory by Einstein. This was the first step in the development of a new basis for physics. Both theories, however are incomplete, and are limited in their abilities to answer many questions. Quantum Physics deals with the behaviour of very small objects, such as atoms, why they do not disintegrate as Newtonian Physics wanted. The theory of Relativity, on the other hand deals with much large scales, celestial bodies and others. Both theories fail when confronted to the other's 'domain', and are therefore limited in their ability to describe the universe. One must unify these theories, make them compatible with one another. The resulting theory would be able to describe the behavior of the universe, from quarks and atoms to entire galaxies. This is the quantum theory of gravity.
Answered by: Christian Kaas, M.A., Phyics Grad Student, IRNP, Paris

There are two fundamental areas of modern physics, each describes the universe on different scales. First we have quantum mechanics which talks about atoms, molecules and fundamental particles. Then we have general relativity which tells us that gravity is the bending and warping of space-time. There has been much work on finding a theory that combines these two pillars of physics. There are three main aproches to quantum gravity all have there problems. 1) Loop quantum gravity.
2) String Theory.
3) Others Penrose spin networks, Connes non-commutative geometry etc.
1) Loop quantum gravity is a way to quantise space time while keeping what General Relativity taught us. It is independent of a background gravitational field or metric. So it should be if we are dealing with gravity. Also, it is formulated in 4 dimensions. The main problem is that the other forces in nature, electromagnetic, strong and weak cannot be included in the formulation. Nor it is clear how loop quantum gravity is related to general relativity. 2) Then we have string theory. String theory is a quantum theory where the fundamental objects are one dimensional strings and not point like particles. String theory is "large enough" to include the standard model and includes gravity as a must. The problems are three fold, first the theory is background dependant. The theory is formulated with a background metric. Secondly no-one knows what the physical vacuum in string theory is, so it has no predictive powers. String theory must be formulated in 11 dimensions, what happened to the other 7 we cannot see? ( Also string theory is supersymmetric and predicts a load of new particles). 3) Then we have other approches, such as non-commutative geometry. This assumes that our space-time coordinates no longer commute. i.e. x y - y x is not zero. This formulation relies heavily on operator algebras. All the theories have several things in common which are accepted as being part of quantum gravity at about Planck scale. i)Space-time is discrete and non-commutative ii)Holography and the Bekenstin bound. i) This is "simply" applying quantum mechanics to space-time. In quantum mechanics all the physical observables are discrete. ii) The holographic principle was first realised by Hawking. He realised that the entropy of a black hole was proportional to the surface area of the horizon and not the volume. That is all the information about a black hole is on the surface of the horizon. It is like a holograph, you only need to look at the 2-d surface to know everything you can about the black hole. Bekenstin showed that there is a maximum amount of information that can pass through a surface. It is quantised in Planck units.
Answered by: Andrew James Bruce, Physics Graduate, UK

'I have deep faith that the principle of the universe will be beautiful and simple.'


What is gravity really? - Sterrekunde

Huh? Magnetism is a force that is invisible to the eye, but can certainly be understood. Same goes for oxygen, radiation, the wind, etc. These don't need to be visible to our eyes to be explained.

Forces are mysterious only if when you do not take the time to fully research them. Don't ask us to reinvent the wheel go and read what the scientists and experts have solved. Of course man understands gravity and magnetism. I studied those decades ago, and they were clearly defined.

Huh? Magnetism is a force that is invisible to the eye, but can certainly be understood. Same goes for oxygen, radiation, the wind, etc. These don't need to be visible to our eyes to be explained.

Forces are mysterious only if when you do not take the time to fully research them. Don't ask us to reinvent the wheel go and read what the scientists and experts have solved. Of course man understands gravity and magnetism. I studied those decades ago, and they were clearly defined.

How does the earth move an apple toward it without touching it?

I understand an automobile can move a trailer because there is something tangible between the two vehicles serving as a link: it's called a hitch.

What is the TANGIBLE LINK between a planet and a falling object being pulled toward it? What is physically connecting the two masses together?


A non-contact force is a force which acts on an object without coming physically in contact with it. The most familiar non-contact force is gravity, which confers weight. In contrast a contact force is a force applied to a body by another body that is in contact with it.

It is as if the root causes of magnetism and gravity are some invisible forms of energy. Certainly, non-contact forces are to some degree paranormal phenomenon but still 100% natural phenomenon.

Paranormal means we can see and feel its effects but can't explain what causes it. We don't know how it ticks.

I can touch wind with my hands and face. The wind (a mass of air) is material. Is there something MATERIAL (something of substance) the earth uses to draw a falling object toward it?

Huh? Magnetism is a force that is invisible to the eye, but can certainly be understood. Same goes for oxygen, radiation, the wind, etc. These don't need to be visible to our eyes to be explained.

Forces are mysterious only if when you do not take the time to fully research them. Don't ask us to reinvent the wheel go and read what the scientists and experts have solved. Of course man understands gravity and magnetism. I studied those decades ago, and they were clearly defined.

Well, actually, no, we don't really understand the mechanism underlying force at a distance (gravity and magnetism). We have very accurately quantified the effects. But the best explanation to date of HOW gravity acts at a distance with no intervening medium (sorry, no luminiferous aethyr) is Einstein's concept that mass creates a warpage in space-time, which means that objects with mass move toward positions of lower gravitational potential. His quantification of this effect was proven when astronomical observations demonstrated the bending of light rays around the sun, but the underlying explanation still remains unsatisfying.

Of course everyone learns the inverse square law of gravitational attraction in high school, and many learn the related laws of magnetic fields in college (Maxwell), but no, the actual fundamental mechanism by which these forces act, at a distance, in a vacuum, is NOT truly understood in the way we understand how water boils or a beam bends under load.

Well, actually, no, we don't really understand the mechanism underlying force at a distance (gravity and magnetism). We have very accurately quantified the effects. But the best explanation to date of HOW gravity acts at a distance with no intervening medium (sorry, no luminiferous aethyr) is Einstein's concept that mass creates a warpage in space-time, which means that objects with mass move toward positions of lower gravitational potential. His quantification of this effect was proven when astronomical observations demonstrated the bending of light rays around the sun, but the underlying explanation still remains unsatisfying.

Of course everyone learns the inverse square law of gravitational attraction in high school, and many learn the related laws of magnetic fields in college (Maxwell), but no, the actual fundamental mechanism by which these forces act, at a distance, in a vacuum, is NOT truly understood in the way we understand how water boils or a beam bends under load.

Man doesn't know what causes it or how it works. We can only observe and measure its effects. Gravity, like another natural non-contact force, magnetism, seems to have no perceivable direct mechanical (material) connection between the two bodies being attracted to one another or repelled from one another.

I can tie a rope to a box and pull the box toward me over the ground. The rope in question is the material means which binds the force exerted by my body with the box. It's a force communication component. A car's transmission communicates force or driving energy through a mass, or a drive shaft, to the rear axle.

Gravity and magnetism both have no apparent ropes, wires, strings or shafts attached between two masses to cause movement between them.

How does the earth move the apple from a tree branch toward the ground without actually touching the fruit?

How does a magnet move a steel ball without touching it?

While they remain hypothetical because they are as yet undetectable, Gravitons, if they exist, are thought to be a massless, stable, spin-2 particle that travels at the speed of light which produce gravity.

In the video below, Neil deGrasse Tyson explains gravitational waves and gravitons. He was speaking before gravitational waves were actually discovered and detected multiple times, so his comment about gravitional waves never having been directly detected is no longer true.

Neil deGrasse Tyson Explains Gravitational Waves and Gravitons


Gravity varies a bit on different parts of the earth because areas of the earth with more mass have stronger gravity than areas with less mass.

Of interest is that some physicists think that dark energy could be a repulsive gravity rather than an attractive gravity and therefore drives the expansion of the universe.


Why is the Gravitational Constant so hard to pinpoint?

At first it may seem strange that the gravitational constant is so hard to determine. There are four fundamental forces in the universe:
• Strong Force
• Weak Force
• Electromagnetism
• Gravity

Gravity is by far the weakest of the four forces, which, may also sound a little strange considering what we see in the universe. When looking out into the cosmos, gravity appears to be the reigning king of all. Gravity is so strong that it causes stars to fuse hydrogen into helium, collapses stellar cores into neutron stars and black holes, creates quasars and dictates the flow of matter within the entire universe.

On a large scale, gravity wins. But, as was previously mentioned, gravity is the weakest of the four forces. The reason for this discrepancy is, as a force, gravity travels further and has a slower fall off. The strongest of the four forces, the Strong Force, becomes almost non-existent at distances outside of a nucleus. What makes gravity stronger in macro circumstances is that it is accumulative. The more matter there is, the more gravity.

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But still, gravity is weaker. Therefore, when trying to measure it, the other forces can cause systematic errors. It is akin to trying to measure the weight of a feather, outdoors, in a slight breeze, with an old pair of scales. The first thought would be to try to remove the other sources of error. We do this by doing several different experiments and then averaging the results. We are not yet aware of a single perfect test to measure the gravitational constant.

Over the last century, nearly every time the gravitational constant has been measured, we’ve observed a different value. At first glance, you may think that means we’re getting closer to its true value however, it is hard to tell. It is currently uncertain as to whether the constant has actually been changing marginally over time or just compounding systematic errors. Another theory is that there many be a correlation between dark energy and gravity. Yet another theory states that the constant is always fluctuating around an average value and that if we keep testing it over an even longer period of time, we will find the true average value.

It is nice to still have mysteries in the universe, things that we done quite understand. Incredibly small changes in the gravitational constant can affect the rate at which stars form, their size and how long they remain on their main sequence. Maybe we will never know for sure, remaining one of the universes true mysteries.

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