With the Higgs Boson in the bank, it’s time for the Large Hadron Collider to tackle physics’ next great unanswered question: why is gravity so weak?

 

On the face of it, gravity would seem to be a pretty impressive force – after all, it is responsible for the formation of planets, stars and galaxies.

Earth and all the other planets of our solar system are held on an invisible leash and forced by gravity to orbit the Sun. But compared to the other fundamental forces, gravity is really very puny.

In fact, it is so weak you would need to increase its strength by 1,000billion, billion, billion, billion times to bring it in line with the strength of the other forces.

While Wile E. Coyote can attest to the power of gravity every time he plunges from a cartoon cliff, when you compare it with electromagnetism you can see just how weak it is.

Gravity is a product of mass – the more massive the object, the greater its gravitational influence is. Gravity pulls matter towards an object’s centre of mass – planets and stars are round because they are made up of atoms of matter that are jostling to get as close as possible to a central point.

What stops all that matter reaching the centre is the electromagnetic force interacting with all those atoms. Gravity is powerless against the overwhelming strength of electromagnetism.

For gravity to overcome the electromagnetic force you need a truly massive object – such as a star. Only in the centre of a star is gravity strong enough to force atoms to overcome their electromagnetic repulsion.

But why is gravity so much weaker than the other forces? No one really really knows – and that irritates the hell out of scientists.

Physicists have a very effective theoretical framework to describe how the Universe works at the quantum level, called the ‘Standard Model’. The theory neatly explains what the fundamental particles do and how they interact with the other fundamental forces. Thanks to the Large Hadron Collider they now have the ‘Higgs Boson’ – a missing piece of the Standard Model, needed to explain where the particles get their mass. But, try as they might, physicists just can’t get gravity to fit.

 

Extra dimensions

To explain the mismatch between gravity and the other forces, physicists have suggested that their may be extra dimensions beyond the three that we are familiar with – up and down, left and right, forwards and backwards. 

In the science fiction world extra dimensions are depicted as alternate universes, or parallel worlds (usual inhabited by the hero’s evil alter ego – to be recognised by darkened eyes and a beard), but, in physics, an extra dimension is rather less dramatic.

For physicists, an extra dimension is just another direction in space on top of the three that we humans use to navigate the world. The extra dimensions are hidden from us because of the way we perceive the universe.

One theory, called string theory (or M-theory), predicts that there are up to ten dimensions and that the extra dimensions are hidden from us because they are curled up in really (really, really) small loops.

If that sounds bizarre, imagine an acrobat balancing on a tight rope. In essence, he is occupying a one dimensional world in which he can move only backwards and forwards.

Now, if we imagine a flea on the same tight rope. The flea can move backwards and forwards on the rope but he can also walk sideways and walk around the rope. The flea is living in a two dimensional world, but one of these dimensions is tiny closed loop.

The acrobat can’t detect the second dimension just as we can’t detect dimensions beyond the three we move about in.

Also, just as we are trapped within our three-dimensional world, so is everything we use to measure the world around us – such as light and sound. With nothing interacting with these other dimensions, we have no way of detecting them.

 

What does this have to do with gravity?

Although all the other fundamental forces are trapped in our three-dimensional world, gravity is thought to be free to travel through these extra dimensions.

As it spreads out through all the extra dimensions it becomes increasingly diluted – making its effect our three-dimensional world much weaker.

 

So how can we test this?

Well, according to the Standard Model, each of the fundamental forces has a special sort of particle called a force carrier associated with it. These force carriers are like messenger boys that carry instructions to other particles telling them how to be influenced by the force.

It is thought that gravity must also have a force carrier particle, called the ‘graviton’. Unfortunately, we have never actually seen a graviton, which is where particle colliders like the Large Hadron Collider come in.

When the LHC smashes protons together, all sorts of particle gubbins fly out the energy maelstrom. Given enough energy, there is a chance that (if it exists) a graviton will be spat out from the collision.

If gravity does permeate all those extra dimensions, there is a chance that the newly produced graviton will immediately disappear as it escapes into one of them. 

So, our best chance of detecting the extra dimensions (which we can’t see) is to find (from among all the other particle mess) a graviton (which may, or may not, exist) disappearing from our plane of existence. 

That is the LHC’s next big task. Sounds like a doddle.

Gravity Probe B gets heavy with gravity

It has taken 52 years, but one of Nasa’s longest-running projects has helped confirm Einstein’s genius once again.

The Gravity Probe B experiment used four perfectly engineered gyroscopic spheres to put two of Einstein’s key predictions about the nature of gravity to test.

His theory of relativity predicted that a massive object, such as Earth, would bend and twist the four-dimensions of space-time (three dimensional space merged with time) around it.

[Gravity Probe B was designed to make ultra-precise measurements of the Earth gravitational effect on space-time – ]
 

Gravity Probe B was launched in 2004, but its development started way back in 1964 and faced colossal technological challenges. The craft had to have the most precise star trackers and gyroscopes ever built and had to operate free from the effects of drag, magnetism and variations in temperature.

This level of precision was required because it was looking for shifts in the alignment of its gyroscopes that equate to the width of a human hair seen from 100 miles away.

The findings are published in the journal Physical Review Letters.

 

The trouble with gravity

For more than two hundred years, Isaac Newton’s law of gravity reined supreme. According to Newton’s theory, the force of gravity acts instantaneously – if the Earth were to become suddenly heavier, then every other object in the solar system would feel the change in the same instant.

But, in 1906, Einstein came along and published his theory of ‘special relativity’, which showed that nothing can travel faster than the speed of light.

The instantaneous nature of Newton’s gravity was incompatible with special relativity’s universal speed limit.

In 1916, Einstein published his theory of ‘general relativity’. According to Newton, space was just the stage on which the laws of physics played their parts. In his general theory, Einstein showed that space and time are also players on the stage. Mass causes space to curve and space causes mass to move.

 

What is ‘Einstein’s’ gravity?

According to Newton, all objects with mass have a gravitational influence on each other – a heavy object pulls lighter objects towards it; a light object is pulled toward a heavy object.

But, according to Einstein, massive objects have no direct influence on each other at all. Instead, gravity is caused by a massive object bending space-time.

Imagine the fabric of the universe to be like a bed sheet (but with more dimensions). If you place a large apple on that sheet, it will make a depression in the fabric of that sheet. Now, if you roll marbles along that sheet they will roll into the depression made by the apple.

Any massive object like a star, or planet, ‘bends’ the ‘fabric’ of the universe (known as space-time) and all less-massive objects travelling through space-time will be drawn into the depression caused by the mass of that object.

All objects with mass (even you and me) distort space-time to a greater, or lesser degree and all things in motion are subject to the influence they exert on space-time. The name we give to this influence is ‘gravity’.

 

What was Gravity Probe B looking for?

Gravity Probe B was designed to test two of Einstein’s predictions regarding the effect that a rotating massive object (like the Earth) has on space-time:

Geodectic effect:

This is the warping effect that a massive object has on space and time around it (like the depression made by the apple on the sheet)

Frame dragging:

This is the amount that a spinning object pulls space and time with it as it rotates (imagine that the apple on the sheet has a sticky surface – if you were to twist the apple, it would pull the fabric around with it)
 

Three Totally Mind-bending Implications of a Multidimensional Universe

10 Dec 2014

Nearly a century ago, Edwin Hubble’s discovery of red-shifting of light from galaxies in all directions from our own suggested that space itself was getting bigger. Combined with insights from a handful of proposed non-Euclidean geometries, Hubble’s discovery implied that the cosmos exists in more than the three dimensions we’re familiar with in everyday life.

That’s because parts of the cosmos were moving further apart, yet with no physical center, no origin point in three-dimensional space. Just think of an inflating balloon seen only from the perspective of its growing two-dimensional surface, and extrapolate to four-dimensional inflation perceived in the three-dimensional space that we can see. That perspective suggests that three-dimensional space could be curved, folded, or warped into a 4th dimension the way that the two dimensional surface of a balloon is warped into a 3rd dimension.

We don’t see or feel more dimensions; nevertheless, theoretical physics predicts that they should exist. Interesting, but are there any practical implications? Can they become part of applied physics?

1. Warp Drive

Teaching about the 4th dimension, physicists have used analogies, like drawings of something called a hypercube, and even the 19th century novella Flatland by Edwin Abbott Abbott. The book imagines two-dimensional beings living on a planar world that has only length and width. Unable to perceive a third dimension, the Flatlanders see only one plane of three-dimensional visitors, kind of like how computed tomography or magnetic resonance imaging shows the body in slices. Two slices through a leg, one a few millimeters up from the other, look almost the same, but a slice through the waist or chest gives a very different picture. We can relate to this analogy, imagining our three-dimensional environment as just one of an infinite number of slices of a four-dimensional environment.

But moving beyond four dimensions, it gets even weirder, and very hard to visualize. The main theory here is called M theory, which is a theory in physics that unites various types of what’s called superstring theory. In M theory there are a bunch of dimensions, either 10 or 11, depending on who explains it to you. In addition to the three we’re familiar with there are compact dimensions. It’s all related to phenomena called branes that vibrate like strings, but what’s most relevant to this discussion is that the extra or compact dimensions don’t necessarily have to remain compact. Like a jack-in-the box, it might be possible to unpack the extra dimensions, says Richard Obousy, director of Icarus Interstellar, a non-profit organization promoting starship research.

“If an advanced civilization learns how to manipulate higher dimensions, they might use them for technology, including warp drive,” Obousy noted to me, the idea being that some kind of controlled decompacting of extra dimensions could have the effect of squeezing or expanding one of the three big dimensions that we know. Engage the compacting effect in front of a starship and the expansion effect to the rear, and you’d have warp drive, like I discussed in a previous post.

But don’t start packing for your Alpha Centauri vacation just yet, because there’s one tiny little complication, which Obousy is the first to admit. So far, we don’t have a shred of evidence that the hypothesized extra dimensions even exist. Someday, soon, we might get some evidence from the Large Hadron Collider, but even then it’s anyone’s guess whether that would lead to a warp drive technology.

2. Time Travel

Time is usually considered a dimension, even if not a spatial dimension, and we’re certainly moving along the time axis just fine. We don’t possess technology to go backward and change history. If we could find a way to go through other dimensions, the balloon analogy tells us it should allow a kind of tunneling to locations that look distant from the perspective of the three dimensions that we perceive.

It is far less clear, however, whether we could tunnel into other time periods, future or past. Any fans of Star Trek know that the philosophy of time travel into the past is mind-boggling, because you could change history, prevent the series of events that caused your existence in the first place, yada, yada, yada. But time travel to the future – accelerating from the usual move into the future of one minute per minute, one year per year – requires no philosophy. Moreover, we know how to do it.

It’s called time dilation, it’s predicted by Einstein’s theory of special relativity, and it will happen, if we accelerate a spacecraft to a significant fraction of the speed of light. Travel very close to the speed of light (c), and time slows down from your perspective and the slowing is quantified by a variable known as the gamma factor. On a ship moving just under 0.87c, the gamma factor = 2; thus, from the perspective of Earth-bound observers, the traveler moves 2 minutes into the future for each minute that seems to go by aboard the ship. At 0.94c, gamma = 3, and it increases more dramatically as the ship approaches light speed asymptotically. At 0.9992c, for instance, gamma reaches 25, which can advance you noticeably into the future if you stay at that speed long enough. Make a round-trip to the star Vega, located 25 light-years away, and two years will pass by for you and your friends aboard the ship (you’ll age two years and accumulate two years of memories), but arriving on Earth you’ll find that you’ve jumped ahead by a half-century.

It really would happen; we’re certain, because time dilation has been proven with subatomic particles in accelerators. We can’t do it right now with people, but the capability for relativistic velocities is only a matter of time (excuse the pun), since it could happen with technology that may be just over the horizon, namely nuclear fusion.

3. Traversable Wormholes

Another means of transport made possible by a multidimensional cosmos is wormholes. When Carl Sagan needed a realistic way for humans to travel interstellar distances for his story Contact, he consulted theoretical physicist Kip Thorne. Working with a couple of his best graduate students at the California Institute of Technology, Thorne worked out the equations showing that, indeed, there was a way: a stable, traversable wormhole, or even a system of such tunnels linking different areas of space-time.

This was more than a decade before Miguel Alcubierre would demonstrate that Einstein’s general relativity theory allowed for Star Trek-style warp drive, so Sagan saw the wormhole concept as the only scientifically-valid means by which his protagonist, Ellie Arroway, could be shuttled through the galaxy quickly enough to meet storyline demands.

An advanced civilization could build a system of wormhole-dependent tunnels connecting different points of the space-time fabric, essentially drawing the departure and arrival points in the fabric into close proximity to one another through a 4th dimension. If we could do it, we could have an entry portal nearby, somewhere in the inner Solar System, that leads to an exit point at our destination, for instance a nearby star system with an Earth-like planet. In science fiction, it’s the concept of a star gate.

Because of mathematically complex findings derived from equations in general relativity known as the Einstein field equations, technology that can warp space, whether for warp drive or traversable wormholes, would require a phenomenon called negative energy. Intuitively it is difficult to visualize what negative energy is, but its existence is consistent with a well-established area of physics known as quantum field theory. In fact, using the technology of quantum optics and a phenomenon called the Casimir effect, physicists have actually produced a kind of negative energy already in tiny quantities (negative vacuum energy). Nature produces it in big quantities, but only by using huge concentrations of gravity, which we can’t produce artificially. According to Eric Davis, Senior Research Physicist at the Institute for Advanced Studies at Austin, Texas, who is an expert on faster-than-light propulsion concepts, the most promising way to do this is with a quantum optic device called a Ford-Svaiter mirror. It’s not something that anyone has built yet, but it can be built. It would concentrate the negative vacuum energy. If you do it with a small Ford-Svaiter mirror, it would produce a mini-wormhole, but Davis says that the device could then be scaled up to make wormholes bigger and bigger, eventually big enough for a spaceship to enter. Navigation to find an exit point would be tricky at first, but it’s theoretically possible to place the Ford-Svaiter mirrors in different points to create a kind of tuner, for instance from somewhere near Earth to a point near an Earth-like planet in a nearby star system. Once the first wormhole is built with stable entry and exit points we’d have a way to go back and forth between Earth and our first interstellar destination. We could explore that star system, and no doubt we would do so particularly if it contains a habitable planet that we could colonize, but we could also use it as a staging point to go further. Thus, little by little, we could create wormhole network of sorts, in our little corner of the galaxy. Or, perhaps, at some point, our tunneling might tap into an already existing network similar to what Sagan imagined. In that case, we’d better make sure to learn the rules, for there might be traffic.

Via Discover Magazine

 

Was our universe born in a wormhole in another universe?

Has science found its first white hole?

Now, five years later, a theory has emerged: it could be a white hole.
A white hole is a theoretical beastie that exists as a set of equations that were a by-product of Einstein’s theory of relativity. It is basically a black hole in reverse. If a black hole is an object from which nothing can escape, then a white hole is an object into which nothing can enter – it can only radiate energy and matter.

[Graphic: How white holes (might) be formed – click to bend spacetime and magnify]

It is relativity that makes white holes super-weird. A black hole represents a pinch in the fabric of the universe (spacetime) where everything is dragged into a single infinitely small point known as a singularity.

Relativity suggests the universe shouldn’t be allowed to get all pointy like this but should always continue in an infinite curve. The solution to this was to suggest that instead of terminating spacetime at a point, a black hole creates a funnel, or worm hole, which feeds out into a white hole in the universe’s past (don’t forget, spacetime is an amalgam of space and time, so if you can bend space, then you can also bend time).

Whether Ralph proves to be the first observed white hole remains to be seen. Many physicists would argue strongly it will not but, until then, it’sexciting to believe that it might be.

 

(excuse me Sir, my brain is full!)

A long time ago in a universe far, far away a giant star is in its death throws. It has shone undiminished for billions of years, faithfully illuminating its corner of the cosmos but, its fuel finally exhausted, it collapses. Its quiet implosion concentrates all of its formerly colossal bulk into a tiny speck, a black hole that bends the fabric of the universe to such a degree that it tunnels into another reality and the star becomes a wormhole. Within the wormhole’s womb, a seed of matter expands to become a whole new universe in which, one day, you will be born, live out your days and die.

This might sound pretty fantastic but a theoretical physicist believes that just such a scenario could answer some of cosmology’s most annoying problems.

One of those problems is gravity. For decades scientists – including Einstein – have struggled to mathematically unite this force with the other fundamental forces (electromagnetism and the strong and weak nuclear forces).

Another problem is the messy reality that our universe is expanding at an ever increasing rate when, theoretically, its expansion should be slowing. The last is more of a question than a problem – what came before the Big Bang?

Big Bang theory maintains that the universe was born from a single point of hyper-concentrated matter (a singularity) and has been expanding from that point ever since. But how did that point get there in the first place?

The answer might lie in an idea first suggested more than 30 years ago – that the seed of the Big Bang was created by a dying star in another universe. This dying star created a black hole with a cosmological plughole at the bottom called an Einstein-Rosen bridge, or wormhole. This wormhole tunnelled from that universe, carrying the seed of our universe with it. In the theoretical reverse of a black hole, known as white hole, it spat the seed out, allowing it to expand to create the universe we know and love.

Despite the age of this theory, physicist Nikodem Poplawski, publishing in the journal Physics Letters B next month, has for the first time made calculations that prove that (on paper at least) such a scenario is possible.

It would answer all those irritating cosmological conundrums. If another universe existed before our own, we could trace gravity back to a time when it was united with the other fundamental forces and it explains the universe’s continued expansion and even what came before the Big Bang.

‘But what came before the Big Bang that formed the universe that created our Big Bang?’, do I hear you ask?

Well, maybe it’s just black holes all the way down