Friday, May 24, 2013

Bukti pertama (tentatif) adanya jagat raya lain

Bentangan angkasa luar yang dipindai dan dipetakan oleh wahana Planck

Telah cukup lama para astrofisikawan dan kosmolog memprediksi adanya jagat-jagat raya lain, selain jagat raya kita sendiri. Menurut prediksi teori dawai (string theory), bisa ada sampai 10 pangkat 500 jagat raya paralel, satu di antaranya jagat raya kita. Bilangan 10 pangkat 500 itu adalah angka 1 yang diikuti angka nol sebanyak 500. Ini dikenal sebagai konsep multiverse yang terdiri atas sejumlah level. Tetapi mereka belum dapat memberi bukti-bukti empiris tentang keberadaan multiverse ini. Kalangan yang menolak teori multiverse menyatakan kita tak akan pernah bisa mengobservasi keberadaan jagat-jagat raya lain secara langsung; dus, mereka mengabaikan begitu saja landasan-landasan teoretis yang telah dibangun untuk melahirkan teori multiverse. 


Wahana Planck dan foto angkasa luar yang berhasil dipindainya

Namun dalam minggu-minggu terakhir ini, diberitakan bahwa bukti pertama adanya jagat-jagat raya lain telah berhasil diperoleh lewat hasil pemindaian dan pemetaan angkasa luar dalam waktu panjang oleh wahana Planck (milik ESA). Bukti pertama adalah adanya anomali dalam pancaran radiasi purba yang tersisa dari big bang 13,8 milyar tahun lalu (radiasi yang disebut sebagai Cosmic Microwave Background Radiation/CMBR), anomali yang muncul (menurut fisikawan Laura Mersini-Houghton, dengan dukungan koleganya Richard Holman) karena adanya tarikan gravitasi dari jagat-jagat raya lain terhadap jagat raya kita ketika mulai terbentuk pada saat big bang. Menurut data wahana Planck, separuh angkasa memperlihatkan radiasi yang lebih kuat dibandingkan di separuh bagian lainnya; padahal seharusnya radiasi ini, kalaupun bervariasi, variasinya sangatlah kecil dalam lingkup galaksi-galaksi atau himpunan galaksi-galaksi; dan dalam lingkup yang jauh lebih luas radiasi ini haruslah tersebar dengan seimbang. Selain itu, ditemukan juga kawasan-kawasan langit yang temperaturnya lebih rendah dari temperatur rata-rata, kawasan yang dinamakan cold spot, yang mengindikasikan kawasan ini berbeda dari jagat raya kita, perbedaan yang dapat terjadi karena dampak adanya jagat-jagat raya lain.


Meskipun demikian, ada juga pakar-pakar lain yang menilai kesimpulan yang ditarik ini spekulatif kendatipun sangat menarik. Bagaimana juga, data Planck yang menunjukkan anomali-anomali statistik tersebut diakui tak dapat dijelaskan lewat cara-cara yang konvensional; jadi, sangat mungkin harus ada cara-cara lain yang masih harus ditemukan untuk menjelaskan fenomena anomali-anomali ini. Sementara ini, pendapat Laura Mersini-Houghton dan Richard Holman adalah pendapat terkuat yang bisa diajukan, meskipun diakui sebagai pendapat sementara (apa sih yang tidak bersifat sementara dalam dunia sains?). 
 

Sumber-sumber

Rose Taylor, "Is our universe merely one of billions? Evidence of the existence of 'multiverse' revealed for the first time by cosmic map", MailOnline, 19 May 2013, pada http://www.dailymail.co.uk/sciencetech/article-2326869/Is-universe-merely-billions-Evidence-existence-multiverse-revealed-time-cosmic-map.html.

Jonathan Leake, "Cosmic cold spots hint at other universes", The Australian News, 19 May 2013, pada http://www.dailymail.co.uk/sciencetech/article-2326869/Is-universe-merely-billions-Evidence-existence-multiverse-revealed-time-cosmic-map.html.



Cosmic cold spots hint at other universe 
by: JONATHAN LEAKE 
From: The Times 
May 19, 2013 11:50AM 

SCIENTISTS believe they have found the first evidence that other universes exist. 

The finding, based on data gathered by the European Space Agency’s Planck spacecraft, implies that our universe could be just one of billions - perhaps an infinite number. Such theories have been discussed by cosmologists for decades - but until now they have lacked any evidence.

A few weeks ago, however, scientists published a spectacular new map of the cosmic microwave background - the “radiation” left behind after the Big Bang that created the universe 13.8 bn years ago.

The map, based on Planck data, showed anomalies in the background radiation that, some cosmologists say, could only have been caused by the gravitational pull of other universes outside our own.

“These anomalies were caused by other universes pulling on our universe as it formed during the Big Bang,” said Laura Mersini-Houghton, a theoretical physicist at the University of North Carolina at Chapel Hill. “They are the first hard evidence for the existence of other universes that we have seen.”

Such ideas are controversial but are attracting growing interest among physicists. This is because Mersini-Houghton, and her colleague Professor Richard Holman, at Carnegie Mellon University, published a series of papers from 2005 predicting what Planck would see. In particular, they predicted that the ancient radiation permeating our universe would show anomalies generated by the pull from other universes.

The scientists analysing the Planck data have now published a paper acknowledging the anomalies exist and cannot be explained by conventional means. “It may be that the statistical anomalies described in this paper are a hint of more profound physical phenomena that are yet to be revealed,” it said.

Planck worked by gathering radiation from when the universe was just 370,000 years old - still glowing from the Big Bang. It has been travelling across space for 13.8 bn years and so is remarkably faint but still detectable. In theory, that radiation should vary a little on the scale of galaxies and clusters of galaxies, but at much larger scales it should be evenly distributed.

In practice, however, Planck’s data shows this is not the case. The radiation is stronger in one half of the sky than the other. There is also a large “cold” spot where the temperature is below average.

Mersini-Houghton will set out her findings in Britain, first at the How The Light Gets In festival in Hay-on-Wye, starting this week, and then at a cosmology conference in Oxford. They are likely to provoke a powerful reaction from other academics, some of whom have spent decades working on alternative theories that will be scrapped if Mersini-Houghton and Holman are proven right.

Malcolm Perry, professor of theoretical physics at Cambridge, said the idea needed work but was “very exciting”. “It is exactly right to say that this could be the first evidence for other universes.”

George Efstathiou, professor of astrophysics at Cambridge, who co-authored the papers setting out the Planck findings, said the suggestion that the data offered evidence for other universes was speculative but “very interesting”.

He added: “Such ideas may sound wacky now, just like the Big Bang theory did three generations ago. But then we got evidence and now it has changed the whole way we think about the universe.” ***