Descobertas inesperadas no “pequeno” experimento do Big Bang deixam os físicos perplexos

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Conceito de Neutrino de Colisão de Partículas

Os cientistas conduziram experimentos ultraquentes no Relativistic Heavy Ion Collider, recriando temperaturas não vistas desde o Big Bang. Os resultados inesperados surpreenderam os físicos.

Uma temperatura não vista desde o primeiro microssegundo do nascimento do universo foi recriada pelos cientistas, e eles descobriram que o evento não se desenrolou da maneira que eles esperavam. A interação de energia, matéria e força nuclear forte nos experimentos ultraquentes conduzidos no Relativistic Heavy Ion Collider (RHIC) foi considerada bem compreendida. No entanto, uma investigação detalhada revelou que os físicos estão perdendo algo em seu modelo de como o universo funciona. Um artigo recente detalhando as descobertas aparece na revista Cartas de revisão física.

“São as coisas que você não esperava que estão realmente tentando lhe dizer algo na ciência”, diz Steven Manly, professor associado de física e astronomia na Universidade de Rochester e coautor do artigo. “A natureza básica das interações dentro do meio quente e denso, ou pelo menos a manifestação dele, muda dependendo do ângulo em que é visto. Não sabemos por quê. Recebemos algumas novas peças do quebra-cabeça e estamos apenas tentando descobrir como essa nova imagem se encaixa.”

“Eles disseram: ‘Isso não pode ser. Você está violando a invariância do boost.’ Mas revisamos nossos resultados por mais de um ano e eles confirmam. — Steven Manly

Manly e seus colaboradores no experimento PHOBOS no RHIC em Brookhaven, Nova York, queriam investigar a natureza da força nuclear forte que ajuda a unir os átomos. Eles esmagaram dois átomos de ouro juntos em velocidades próximas à velocidade da luz na tentativa de criar o que é chamado de “quark-gluon”.[{” attribute=””>plasma.” This is a very brief state where the temperature is tens of thousands of times higher than the cores of the hottest stars.

Particles in this hot-soup plasma stream out, but not without bumping into other particles in the soup. It’s a bit like trying to race out of a crowded room—the more people in your way, the more difficult to escape. The strength of the interactions between particles in the soup is determined by the strong force, so carefully watching particles stream out could reveal much about how the strong force operates at such high temperatures.

To simplify their observations, the researchers collided the circular gold atoms slightly off-center so that the area of impact would not be round, but shaped rather like a football—pointed at each end. This would force any streaming particles that headed out one of the tips of the football to pass through more of the hot soup than a particle exiting the side would. Differences in the number of particles escaping out the tip versus the side of the hot matter could reveal something of the nature of that hot matter, and maybe something about the strong force itself.

But a surprise was in store. Right where the gold atoms had collided, particles did indeed take longer to stream out the tips of the football than the sides, but farther from the exact point of collision, that difference evaporated. That defied a treasured theory called boost invariance.

“It may be that we have an actual clue here that something fundamental is different—something we just don’t understand.” — Steven Manly

“When we first presented this at a conference in Stony Brook, the audience couldn’t believe it,” says Manly. “They said, ‘This can’t be. You’re violating boost invariance.’ But we’ve gone over our results for more than a year, and it checks out.”

Aside from revealing that scientists are missing a piece of the physics puzzle, the findings mean that understanding these collisions fully will be much more difficult than expected. No longer can physicists measure only the sweet spot where the atoms initially collided—they now must measure the entire length of the plasma, effectively making what was a two-dimensional problem into a three-dimensional one. As Manly says, this “dramatically increases the computing complexity” of any model researchers try to devise.

Modeling and understanding such collisions are extremely important because the way that the plasma cools—condensing like steam turning into water against a shower door—might shed some light on the mechanism that gives matter its very mass. Where mass itself comes from has been one of physicists chief conundrums for decades. Manly hopes that if we can understand exactly why the quark-gluon plasma behaves as it does, we might gain an insight into some of the rudiments of the world we live in.

“Understanding all the dynamics of the collision is really critical for actually trying to get the information we want,” says Manly. “It may be that we have an actual clue here that something fundamental is different—something we just don’t understand.” Smiling, he adds, “Yet.”





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