![]() ![]() ![]() The conjecture, if true, would mean the density of dark energy in our universe cannot be constant, but must instead take a form called “quintessence”-an energy source that will gradually diminish over tens of billions of years. (So-called anti–de Sitter universes, with stable, negative doses of vacuum energy, are easily constructed in string theory.) You think you should be able to construct them, but you cannot.”Īccording to this “de Sitter swampland conjecture,” in all possible, logical universes, the vacuum energy must either be dropping, its value like a ball rolling down a hill, or it must have obtained a stable negative value. “They almost look like landscape you can be fooled by them. But if Vafa is right, such efforts are bound to sink in logical inconsistency de Sitter universes lie not in the landscape, but in the “swampland.” “The things that look consistent but ultimately are not consistent, I call them swampland,” he explained recently. String theorists have struggled mightily since dark energy’s 1998 discovery to construct convincing stringy models of stable de Sitter universes. Vafa and colleagues contend that universes with stable, constant, positive amounts of vacuum energy, known as “de Sitter universes,” aren’t possible. In addition, it looks like the amount of dark energy infused in empty space stays constant over time (as best as anyone can tell).īut the new conjecture asserts that the vacuum energy of the universe must be decreasing. Since 1998, telescope observations have indicated that the cosmos is expanding ever so slightly faster all the time, implying that the vacuum of empty space must be infused with a dose of gravitationally repulsive “dark energy.” But it violates two widespread beliefs about the actual universe: It deems impossible both the accepted picture of the universe’s present-day expansion and the leading model of its explosive birth. The rule appears to be true in all simple string-theory-based models of universes. The conjectured formula- posed in the June 25 paper by Vafa, Georges Obied, Hirosi Ooguri, and Lev Spodyneiko, and further explored in a second paper released two days later by Vafa, Obied, Prateek Agrawal, and Paul Steinhardt-says, simply, that as the universe expands, the density of energy in the vacuum of empty space must decrease faster than a certain rate. He recalls thinking, “This is so exciting. Wrase has already written two papers, including one that may lead to a refinement of the conjecture, and both mostly while on vacation with his family. Researchers have set to work trying to test the conjecture and explore its implications. Because if this conjecture was right, then it has a lot of tremendous implications for cosmology.” There was confusion, he adds, but “also, of course, huge excitement. “There were people who immediately said, ‘This has to be wrong,’ other people who said, ‘Oh, I’ve been saying this for years,’ and everything in the middle,” Wrase says. That same day, in Okinawa, Japan, Vafa presented the conjecture at the Strings 2018 conference, which was streamed by physicists worldwide. If the conjecture is correct, Wrase and other string theorists immediately realized, the cosmos must either be profoundly different than previously supposed or string theory must be wrong.Īfter dropping his kindergartner off that morning, Wrase went to work at the Vienna University of Technology, where his colleagues were also buzzing about the paper. * String theorists like Wrase and Vafa have strived for years to place our particular universe somewhere in this landscape of possibilities.īut now, Vafa and his colleagues were conjecturing that in the string landscape, universes like ours-or what ours is thought to be like-don’t exist. The theory permits some 10 500 different solutions: a vast, varied “landscape” of possible universes. The leading candidate for a “theory of everything” weaving the force of gravity together with quantum physics, string theory defines all matter and forces as vibrations of tiny strands of energy. The paper, by the prominent string theorist Cumrun Vafa of Harvard and his collaborators, conjectured a simple formula dictating which kinds of universes are allowed to exist and which are forbidden, according to string theory. STRINGS THEORY STILL STRING FULLOne title startled him into full consciousness. ![]() On June 25, Timm Wrase awoke in Vienna and groggily scrolled through an online repository of newly posted physics papers. ![]()
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