Have Scientists Really Discovered a Huge Source of Antigravity?

Transcript

Movement through space is inevitable. Right now,  you’re sitting on a planet that is spinning on its   axis, moving you at up to 1,600 km/h, depending  on your latitude. The Earth circles the Sun,   the Sun moves through the Milky Way, the Milky 

Way moves through the Local Group of galaxies,   and the Local Group moves through our local  Supercluster. And even that Supercluster of   galaxies is in motion, heading towards the Shapley  Supercluster, where scientists believe that there   is a particularly large concentration of galaxies. I hope all this motion isn’t making you too dizzy.  But on the grandest scales of our universe, 

something strange is happening. Scientists have   begun to realise that there is not enough mass in  the Shapley Supercluster to pull us towards it at   the rate that we see; about 50% of the cause  of that motion is unaccounted for. In 2017,   researchers discovered a possible 

source for the rest of that motion.  But it’s not something pulling  us. It’s something pushing.  I’m Alex McColgan, and you’re watching Astrum.  Join with me today as we explore the evidence   for the region of space known as the  Dipole Repeller, and try to understand   how in a universe filled with gravity, 

something can push us instead of pull.  Let’s start with a little context. It’s taken  a long time for astronomers to recognise that   this motion was taking place. To understand  that we were moving, scientists first had to   make a map of the regions of space around us, 

and although we as a species have been mapping   the stars since the beginnings of civilisation,  it was only thanks to Mr. Hubble in 1924 that   we proved there are actually stars in other  galaxies outside the Milky Way. Before then,   although astronomers had seen fuzzy little 

clusters of lights in the night sky that we   now know to be galaxies, the common wisdom was  that these were gas-cloud “spiral nebula” within   the Milky Way, not something that existed beyond  it. Hubble noticed several Cepheid stars - a type   of variable star with a cycle of variation  closely linked to their luminosity - within   one such spiral nebula, and used the fact that 

this luminosity was very predictable based on   distance to calculate very precisely how far  away they were. Surprising many, he proved   that they had to exist beyond the Milky Way. Since then, astronomers have been scrambling   to catch up with the new reality of galaxies  and superclusters, and set about mapping the   locations and distances to every galaxy they 

could find. Hubble had been studying Andromeda,   our closest neighbouring major galaxy, but there  were others. By the 1970’s, Stephen Gregory,   Laird Thompson, and William Tifft definitively  proved that galaxies didn’t just float randomly   in space, but converged into Superclusters – 

large filamentary or sheet-like structures that   exist between large bubbles of void. They mapped  the first Supercluster – the Coma Supercluster,   which covered a region of space 100 million  light-years across. A whopping 95% of all galaxies   are found in these superstructures.

It wasn’t until 2014 that our own   supercluster – the Laniakea Supercluster – was  fully mapped. You might be surprised to hear   it happened in that order. After all, wouldn’t  common sense say it’s easier to map regions of   space closer to us, rather than ones further 

away? Why was it only nearly a century after   the discovery of other galaxies existing, and  40 years after mapping the first supercluster,   that we finally turned to our own? The answer is  that mapping the local regions of space around us   is surprisingly challenging. And it’s all because  of the Milky Way getting in the (Milky) way.  The Milky Way is full of gas and dust, and 

these regions are so difficult to penetrate   that we can’t really see beyond them. Towards  the centre of the Milky Way, this effect gets   so bad that scientists have dubbed the whole area  the Zone of Avoidance – very little light gets   through it. Not being able to see in this area is 

particularly relevant to our current discussion,   for reasons we’ll get to later. In contrast to our local area,   distant galaxies are easier to study, as  all you have to do is point your telescope   at a single point in the night sky, and let it  drink in the light. Mapping the area around us   requires looking at every point in the night 

sky. It’s proved quite difficult, although   astronomers are now getting a better handle on it. Thanks to their efforts in looking at thousands of   galaxies in our galactic neighbourhood,  and by studying galaxies' “peculiar   motion” – their motion relative to the cosmic  background radiation, that ignores the expansion   of the universe – scientists have been able 

to group gravitationally bound galaxies into   Superclusters. At the centre of our Laniakea  Supercluster lies a point known as the Great   Attractor, an area 150-250 million light  years away from us, that we in the Milky Way   are slowly drifting towards. Sadly, the Great 

Attractor lies within the Zone of Avoidance,   so it’s tricky to see clearly what lies there. To confound things further, the Laniakea   Supercluster was also found to be moving. It  travels towards another supercluster, known as the   Shapley Supercluster, taking us along with it. At 

the centre of this supercluster lies the Shapley   Attractor, which also is believed to be incredibly  dense in terms of mass. But frustratingly,   this second attractor also lies in the  zone of avoidance, making it difficult   to see exactly what’s going on over there, too. Thankfully, as x-ray and infra-red telescopes   improved, it became possible to take a better 

look at these two attractors. But this is where   the mystery begins. What mass is there  is not quite massive enough to account   for our apparent motion in that direction.  Which is why a team of researchers from the   University of Hawaii published an article in 

Nature to attempt to explain this discrepancy. The team was made up of Yehuda Hoffman, Daniel  Pomarède, R. Brent Tully & Hélène M. Courtois.   Together they created a new kind of map of 

the local universe around us. This time,   instead of simply noting galaxies’ positions,  they highlighted their motions instead.   This allowed them to create a map of flow  lines, which after mathematical analysis,   allowed them to make assumptions about the  locations of masses in our nearby superclusters.   Their results were surprising.

A lot of our local  mass is moving towards the Shapley Supercluster,   which is what you would expect. But they also  found a lot of mass is moving away from another   specific region in space. They called this 

mystery patch of space the “Dipole Repeller.”  Together, the Dipole Repeller and the Shapley  attractor both contribute about 50% to our motion,   working together in tandem (hence the name  “Dipole”). But how? Gravity is a force that,   so far as we have observed, only pulls. What 

lies in this region of space that allows a push   to happen? Could it be a strange collection  of white holes, the theoretical opposite of   black holes that we’ve talked about in videos  before? Or perhaps, some source of anti-gravity?  Not quite. The answer is… nothing. The Dipole Repeller is a void – a bubble   about 100 million light years across, that does 

not contain many if any major galaxies. It’s one   of the bubbles that exists between the filaments  of the universe’s structures. But interestingly,   our galaxy’s current motion lines up much more  satisfyingly with the push from this region,   than it does from the pull of the Shapley 

attractor, which is a compelling argument   in this theory’s favour. So, how does nothing push?  The answer is actually that this could be  a pseudo-force, more than it is a real one.   Imagine a universe where all the galaxies  were spaced equally. While the gravity of   galaxies above you would pull you, the 

gravity of galaxies below you would do   the same. So would the pull of galaxies to your  left and to your right. In this way, the varying   forces of all these gravities would balance each  other, leaving you to not really travel in any   direction – you’d be in perfect equilibrium.

But what would happen if we removed the   galaxies from one of these directions?  What would happen if we added a void?  Well, then the scales would tip. There would be  one direction that no longer pulled you, leaving   the opposite direction’s pull to act on you  unimpeded.

As a result, you would move away from   the void, as if it were pushing you. Everything  near a void will thus move away from it,   making it seem to have a repelling gravitational  force. It is something of an optical illusion.  There is another explanation for why a void space 

might push you, which might work in tandem with   this pseudo force. The universe is expanding, and  that expansion shows no sign of slowing down – in   fact, it seems to be speeding up. However,  this expansion is counteracted by gravity,   and in areas where there is more gravity, less 

expansion seems to take place - stars aren’t   just being pushed away from each other, they  are also being pulled together. Conversely,   in a void, there is nothing to contain  this rampant expansion. As a result,   void spaces literally will swell compared to 

their supercluster counterparts. It might be   done by warping the fabric of reality,  but this also achieves a sort of “push”.  Since 2017, not much more has come to light about  the existence of the Dipole Repeller. As this is   still an expanding field of research, there’s 

some debate about whether it’s really there,   or how influential it might be on our galaxy’s  current motion. It is difficult to observe,   due to the Milky Way’s obscuring effect, and there  is always a challenge inherent in trying to spot   the absence of a thing, rather than its presence.  However, Tully and his fellow researchers hope   that with the aid of future ultra-sensitive 

surveys in multiple spectrums of light,   it will be possible to map out the few galaxies  that lie in this void, and generally confirm its   existence in the region they hypothesise. We are constantly moving through space,   but even the science of space is always in motion.  Each new galaxy, along with data regarding its   redshift and travel speed, helps us develop a  broader understanding of the movement of the   universe.

It’s fascinating to think that not all  of that motion is caused by the pull of gravity.  It might turn out that, sometimes, the  universe just needs a little push to get going. There have been a lot of awesome images in  Astrum videos over the years.

Sometimes,   the visuals we show in our videos are so  colourful, so grand, and so awe-inspiring,   that the short 3 second clip doesn’t  really do them justice. In those cases,   I felt it would be really cool if there was a  way to come back to these images again and again,   to relive the magic of those moments, and capture 

the power and enormity of space. To that end,   I’ve spent the last couple of months working  with artists to develop 70x50cm posters that   captures those epic moments. We’ve created a set  of premium prints that look great and act as a   daily reminder of the Universe that surrounds 

us, perfect for bringing grandeur to your wall   or as an inspiring motif in your office space.  Follow the link electrify.art/ASTRUM to check   them out and let me know what you think  of them actually in the comments below!