A new antiproton decelerator experiment has revealed stunning new insights into gravity and antimatter. <\/p>
According to first Newton, then Einstein, and now an experiment at CERN<\/a>, gravity is an attractive force that exists between all objects in the Universe.<\/p> That includes objects that have no mass, because gravity<\/a> acts on energy, and mass is just one form of energy (as Einstein\u2019s most famous equation states, energy is equal to mass multiplied by the square of the speed of light<\/a>). This is why even massless photons of light, travelling from distant stars, have their paths bent as they pass massive galaxies on the way.<\/p> Antigravity is a hypothetical repulsive gravitational force. In some ways, it sounds obvious that it should exist. There are both attractive and repulsive electric forces, so why not the same for gravity?<\/p> The difference is that electric charge comes in two types, positive and negative. Positive and negative charges attract each other, while charges that are alike repel each other. The equivalent of \u2018charge\u2019 for gravity is energy, and it only comes in one type \u2013 positive.<\/p> As these positive energies attract each other there, doesn\u2019t seem to be room for antigravity, which is a pity because it would be a great way of flying around without the need for rockets, jet engines or even wings.<\/p> However, there is (or was, until this month) a possible get-out clause for antigravity: antimatter.<\/p> Antimatter is not hypothetical, it is very real. Particles such as electrons have an antimatter equivalent. The antiparticle of the electron is the positron, and it has not only been observed, but is regularly used in hospitals for diagnostic purposes.<\/p> Positrons emitted from unstable elements injected into a patient\u2019s body will give off a very distinctive energy signal when they meet an electron and annihilate. The signal is so distinctive that the point of annihilation can be identified very precisely.<\/p> The whole process, known as Positron Emission Tomography, gives doctors unique information on the soft tissues and flow of material around a body.<\/p> Antimatter has the opposite electric charge to matter, so does it also have the opposite gravitational charge, and so experience antigravity? This was the question the ALPHA-g experiment at CERN was designed to answer. Does antimatter fall down or up?<\/p> Producing antiparticles is quite easy. Accelerators such as those at CERN can make many positrons and anti-protons. That\u2019s fine, but these particles have electric charge, and they are also in general moving at high speed. Neither of those things is good if you want to measure the effect of gravity, because gravity is really, really weak.<\/p> Just think: your muscles, which use the electromagnetic force, can pick up a pen or paper, thereby counteracting the combined gravitational attraction of an entire planet.<\/p> So any tiny stray electric field in your experiment could easily obscure the effect of gravity on a charged particle like a positron or antiproton. And anyway, they will have sped away before you could see which way they fall.<\/p> The antiproton decelerator at CERN is designed to combat this; to slow down antiprotons, and eventually bring them together with positrons to make electrically neutral antihydrogen. In a similar way in which an atom of hydrogen is made up of a single proton and an electron, an atom of antihydrogen is made up of a single antiproton and a positron.<\/p> Read more:<\/strong><\/p> The ALPHA experiment has been collecting antihydrogen atoms and studying them since 2013, and this month they published results from a new setup, called ALPHA-g, where the g stands for gravity.<\/p> The idea is very simple \u2013 trap a few hundred antihydrogen atoms in a vertical tube, let them diffuse around, and measure how many come out of the top and how many come out of the bottom.<\/p> The experimental set-up is such that if gravity affects antimatter in the same way it affects matter, 80 per cent of them should drop out of the bottom, while 20 per cent would diffuse out of the top of the experiment by ‘bouncing’ up.<\/p> Within the precision of the experiment, this is what happened. Antimatter falls down, like normal matter.<\/p> Now, is this the end of the road for antigravity?<\/p> Not really.<\/p> But it is the end for a certain type of antigravity. We won\u2019t be getting antigravity rockets (or hoverboards) riding on a cushion of antimatter.<\/p> However, while most scientists are profoundly unsurprised by this result, a form of antigravity is actually built into our current best understanding of cosmology.<\/p> Astrophysical measurements indicate that the rate of expansion of the Universe is increasing, meaning that some force is counteracting the gravitational attraction between the matter in the Universe, and actually pushing it apart. We call this dark energy but we could just as well have called it \u201cantigravity\u201d.<\/p> In fact, there were even cosmological theories which proposed that half the Universe was made up of antimatter, and this was repelling the matter and thus providing the dark energy effect.<\/p> Such ideas also potentially solved some other problems with our understanding of cosmology \u2013 although they created a whole bunch more. Either way, in light of the ALPHA-g result, it seems they are wrong, and there must be something else behind the antigravity effect of dark energy.<\/p> Read more about physics:<\/strong><\/p> A new antiproton decelerator experiment has revealed stunning new insights into gravity and antimatter. <\/p>\n","protected":false},"author":24,"featured_media":34976,"template":"","categories":[1],"acf":{"readingTimeMinutes":"5"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2023\/10\/why-dark-energy-could-keep-the-dream-of-anti-gravity-alive.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"A new antiproton decelerator experiment has revealed stunning new insights into gravity and antimatter.","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/rss_feed\/34975"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media\/34976"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media?parent=34975"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/categories?post=34975"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Why antimatter matters<\/strong><\/h2>
A new antigravity mystery<\/strong><\/h2>
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