Cosmology

Shortcomings of the Standard Cosmology

Despite the self-consistency and remarkable success of the standard Hot Big Bang model in describing the evolution of the universe back to only one hundreth of a second, a number of unanswered questions remain regarding the initial state of the universe.

The flatness problem

Why is the matter density of the universe so close to the unstable critical value between perpetual expansion and recollapse into a Big Crunch?

The horizon problem

Why does the universe look the same in all directions when it arises out of causally disconnected regions? This problem is most acute for the very smooth cosmic microwave background radiation.

The density fluctuation problem

The perturbations which gravitationally collapsed to form galaxies must have been primordial in origin; from whence did they arise?

The dark matter problem

Of what stuff is the Universe predominantly made? Nucleosynthesis calculations suggest that the darrk matter of the Universe does not consist of ordinary matter - neutrons and protons?

The exotic relics problem

Phase transitions in the early universe inevitably give rise to topological defects, such as monopoles, and exotic particles. Why don't we see them today?

The thermal state problem

Why should the universe begin in thermal equilibrium when there is no mechanism by which it can be maintained at very high temperatures.

The cosmological constant problem

Why is the cosmological constant 120 orders of magnitude smaller than naively expected from quantum gravity?

The singularity problem

The cosmological singularity at t=0 is an infinite energy density state, so general relativity predicts its own breakdown.

The timescale problem

Are independent measurements of the age of the Universe consistent using Hubble's constant and stellar lifetimes?

A Brief History of the Universe

The history of the Universe divides roughly into three regimes which reflect the status of our current understanding:

• Standard cosmology
• Particle cosmology
• Quantum cosmology

The standard cosmology is the most reliably elucidated epoch spanning the epoch from about one hundredth of a second after the Big Bang through to the present day. The standard model for the evolution of the Universe in this epoch have faced many stringent observational tests.

Particle cosmology builds a picture of the universe prior to this at temperature regimes which still lie within known physics. For example, high energy particle acclerators at CERN and Fermilab allow us to test physical models for processes which would occur only 0.00000000001 seconds after the Big Bang. This area of cosmology is more speculative, as it involves at least some extrapolation, and often faces intractable calculational difficulties. Many cosmologists argue that reasonable extrapolations can be made to times as early as a grand unification phase transition.

Quantum cosmology considers questions about the origin of the Universe itself. This endeavours to describe quantum processes at the earliest times that we can conceive of a classical space-time, that is, the Planck epoch at 0.0000000000000000000000000000000000000000001 seconds. Given that we as yet do not have a fully self-consistent theory of quantum gravity, this area of cosmology is more speculative.

Chronology of the Universe

The following diagram illustrates the main events occurring in the history of our Universe. The vertical time axis is not linear in order to show early events on a reasonable scale. The temperature rises as we go backwards in time towards the Big Bang and physical processes happen more rapidly. Many of the transitions and events may be unfamiliar to newcomers; we shall explain these in subsequent pages.

Orders of magnitude

The timescales and temperatures indicated on this diagram span an enormous range. A cosmologist has first to get the order of magnitude (or the power of ten) correct. Quantities which are given as 10 to some power 6 (say) are simply 1 followed by 6 zeros, that is, in this case 1,000,000 (one million). Quantities which are given as 10 to some minus power -6 (say) have 1 in the 6th place after the decimal point, that is, 0.000001 (one millionth). At extremely high temperatures we tend to use gigaelectron volts (GeV) instead of degrees Kelvin. One GeV is equivalent to about 10,000,000,000,000K.

Scientists create cloaking device that 'hides' whole events - making time itself disappear

Most of the human race don't have any problem making time disappear - but scientists have cracked a very hi-tech way of doing exactly that. 

Scientists have developed a 'temporal cloaking' device that can hide events from view.

The demonstration 'hid' events for 40 trillionths of a second - or 40 picoseconds - by speeding up and slowing down different parts of a light beam.

The different parts of the light beam were then put back together, so that any observers could not detect what happened during the 'hidden' time.

The information is simply not there to be read or reconstructed.

So far, the technique only works on periods of 0.00012 of a second - so the police can probably rest easy, as evildoers would have to move far faster than human beings ever could to 'conceal' their actions.

Instead, the 'hidden' fractions of a second could be used for ultra-secure communications.

The scientists think that the technique could even be combined with recent advances in optical 'cloaking' - to hide an event in both space and time.

 

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Professor Robert Boyd and Dr Zhimin Shi, of Rochester University in New York, reviewed the paper for the journal and said: ‘As if the idea of a device that makes an object seem invisible was not mind-boggling enough, researchers have now demonstrated a system that can conceal an event in time.

‘Because spatial and temporal cloaking work in different physical dimensions - space and time, respectively - there is no fundamental reason why the two techniques cannot be combined so that full spatial-temporal cloaking could be turned on or off at will.

In this 2011 illustration, provided by Cornell University, scientists demonstrate how they have have created, a new invisibility technique that doesnít just cloak an object but masks an entire event

‘Nonetheless, what Fridman et al. have demonstrated as a first temporal cloaking device could already be useful in some applications, such as enhancing the security of communication in fibre-optic systems.  

‘Future directions may include increasing the cloaking time towards the order of microseconds to milliseconds, and building a device that can work simultaneously for incident light coming from different directions.’ 

The demonstration 'hid' events for 40 trillionths of a second - or 40 picoseconds - by speeding up and slowing down different parts of a light beam

The effect is achieved using a split time-lens that breaks light up into slower and faster 'components' - thereby creating a tiny temporal gap. It works by compressing the light passing through a fibre optical cable with a special lens that causes some to speed up and some to slow down

They were able to conceal time for 40 trillionths of a second - or 40 picoseconds - by speeding up and slowing down different parts of a light beam.

Theoretically, anything happening in that tiny gap would be invisible and undetectable, because it would not exist in our perception of time.

The device could be used for ultra-secure communications - or, in one sci-fi scenario, could even be combined with an optical invisibility device, cloaking the user from both space and time, researchers say.

The effect is achieved using a split time-lens that breaks light up into slower and faster 'components' - thereby creating a tiny temporal gap.

Unlike other cloaking devices that work by bending light around objects, this works by compressing the light passing through a fibre optical cable with a special lens that causes some to speed up and some to slow down.

This makes the waves divide and another lens a little further up the cable then causes the light to be put back together.

The result is light emerging from the end of the cable that appears to be unaltered which means for the space between the lenses things have or could have gone on - with no record of it occurring.

Professor Moti Fridman, of Cornell University in New York, and colleagues said a 'time hole' in the probe beam hides the occurrence of an event from the observer.

They said: ‘This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap - inside which an event occurs - such that the probe beam is not modified in any way by the event.

‘The probe beam is then restored to its original form by the reverse manipulation of the dispersion.  ‘In summary we have presented the first experimental demonstration of temporal cloaking that successfully hides an event from a probe beam in the time domain.

‘Our results represent a significant step towards obtaining a complete spatio-temporal cloaking device.’ Physicists have already found ways to make invisibility cloaks by distorting electromagnetic fields and steering light around a volume of space so that, essentially, anything inside this space is invisible.

Prof Fridman's researchers were able to take that idea a step further and cloak time.

They built a device that has two lenses called an electro-optic modulator. Next, they sent a beam of light through the lenses. The first lens compressed the light, while the second lens decompressed it, leaving a short gap or hole, in time where any event went unrecorded.

To the naked eye, light coming out of the second time-lens appeared uninterrupted, as if no distortion had occurred.

In essence, between the two lenses exists a space-time void that cloaks any changes occurring in the short amount of time it takes the light to pass through both lenses.

If coded messages could be hidden in a series of these cloaks it would be very difficult to intercept them - making for very secure communications.

On the other hand if such a hidden time lag could be made to pulse on and off it could be used to intercept data passing through without there being a record of it.

And if the technology could be expanded in theory you could step between two lenses and do anything you wish and it would never be recorded in time - for the rest of the world it would never have happened.

But the researchers whose breakthrough is reported in Nature don't expect the technique could ever produce a gap that lasts any longer than 0.00012 of a second - not nearly enough time to do anything worth hiding.

Space Elevator Low Down

Mike Nowak  10.24.05

With the flick of a switch, a searchlight beam illuminated a photovoltaic array, and a prototype space elevator called Snow Star One lifted off the ground. As the humble assemblage of solar cells, metal braces and off-the-shelf rollers rose slowly from the launch pad and up a long blue tether, a small crowd of spectators let out a boisterous cheer.

The contraption, designed by University of British Columbia undergrads Steve Jones and Damir Hot, didn't get very far -- it managed to wriggle its way just 15 feet up the 200-foot-long tether before stalling out. But as the first competitor in the inaugural Space Elevator Games, even that modest performance was enough to cause a quite stir in the still-embryonic space elevator community.

The games, sponsored by the nonprofit Spaceward Foundation, were held over the weekend at the NASA Ames Research Center in Mountain View, California. Teams competed in one of two events: a light-beam-powered robot climbing competition and a tether-strength contest.

According to many engineers, within a couple of decades it will be both possible and cost-effective to construct a fixed line from the Earth's equator to a satellite 60,000 miles out in space. The tether would likely be made of carbon nanotubes, a still-experimental material with the potential to be 300 times stronger than steel. According to current imaginings, elevator cars weighing up to 20 tons would go up and down, powered by high-intensity earthbound lasers aimed at photovoltaic cells on their undersides.

But with both nanotubes and beam power still a long way off, NASA has decided to try to speed things up by offering prizes to innovators who reach key development milestones in the next few years.

On the beam-power side, the challenge at the games was to use a 10,000-watt light source to send a robot 50 meters up the ribbon in under 50 seconds. For the tether competition, the goal was to construct a 2-gram tether that would be tougher than a 3-gram band made from a high-strength material called Zylon. The best-performing robot and tether, had they beaten those figures, would have earned their owners $50,000 each.

At the climbing competition, however, it wasn't just Jones and Hot that had trouble making it all the way to the top. A contingent of engineering students from the University of Saskatchewan did manage to send their climber 40 feet in the air. But none of the five other teams was able to corral enough power from the searchlight even to get off the launch gantry.

Despite the lackluster performance, however, most participants were upbeat about the proceedings. Hot, for one, was ecstatic. "It's the first beam-powered climber ever," he said. "So we're very proud. In fact, we're beaming."

Entrants in the tether-strength competition had a bit more luck, with one group narrowly missing the prize with a tether made out of Spectra, a material often used in body armor.

But despite this near-victory, Spaceward Foundation rep Marc Schwager claimed that real advancements in tether strength won't be possible until carbon nanotubes arrive on the scene -- something he hopes will happen as soon as next year's games.

Schwager, however, was sanguine about the outcome of the games as a whole. "I would have loved to see somebody win the prize," he said. "But what we're about is bringing attention and focus in this area, and that was successful. And pretty much all the contestants want to come back next year."

Spaceward board member Michael Laine, president of a Bremerton, Washington-based company called LiftPort that is seeking to commercialize space-elevator technology, noted that next year's games will up the ante considerably. While the already daunting thresholds will be set even higher, there will also be more money to entice competitors -- $100,000 for first prize, $40,000 for second and $10,000 for third.

"I think that next year is going to be big," Laine said. "It's going to be harder, but I think there's going to be lots of people that rise to the challenge. We're at the beginning of something really great."