Megatrends Driven by Exponentially Growing Technologies

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Megatrends are large, transformative global forces that impact everyone on the planet.  EY Megatrends Report 2015

Some examples of megatrends:  To introduce the subject, I start by mentioning three megatrends that are not technology driven but are well established. Megatrends are like supertankers whose direction is very difficult to alter - once established they evolve with time and their consequences require co-operative efforts from all nations of the world.
1. Demographic Shifts:  It is projected that global population will increase by more than 1.5 billion by 2050.  There are three trends in this shift:  
     a.  Population increase will be highest in African and Middle Eastern countries who will be responsible for 50% of global population increase. Japan and Russia might actually see a decline of about 15%.   
     b.  65 years or older will triple from 500 million in 2010 to 1500 million in 2050.
     c.  Spending power of the global middle class will increase from US$21 trillion in 2010 to $56 trillion in 2030.  Middle Class in Asia-Pacific countries will increase their share from 24% to 56%.
2. Shift to Cities:  Global urban population will increase from 3.8 billion in 2010 to 4.9 billion in 2030 and 6.5 billion by 2050. 1.5 million people are added to global urban population every week. 

  
3. Climate Change: Climate change will impact on agriculture and food resources, demand for which is expected to increase by 40 percents by 2030.  Extreme weather will devastate many areas and rising sea levels will also seriously affect big cities near coastlines. Center for Global Development has an interactive website for mapping the impacts of climate change that is worth a visit and some mouse-work.

Megatrends happen as a result of complex interplay between social, industrial, economic and technological developments. This blog concerns with megatrends engendered and supported by growth in technology and analyses how these impact our social, industrial and personal development.

Not a day goes by when I do not come across the phrase - Technology is growing exponentially.  To my mind, exponential growth eventually brings an unimaginable rate of change.  Humans perceive the world in a linear fashion where things around them change in an incremental fashion and extrapolation over a period - days or even decades - may be easily perceived.  This is how humans have lived since the beginning - the past 100 years excepted when consequences of exponential growth have been felt. 
A good illustration of exponential growth is to work out how population of a bacterial colony increases with time. A single bacterium that doubles in number every minute will grow to a population of more than a trillion trillion after one hour - half of these will be produced in the final minute!

For a fascinating account of exponential growth - click here

Technology is now growing exponentially - the doubling rate of many capabilities follows the so called Moor's Law and is measured in a small number of years.  A technological capability that doubles every year will be a trillion trillion times more advanced in 60 years.  In the following, I show some trends in technologies in three area over the past half century:

The increased technological capability feeds itself into our society in many ways - industrially, it becomes more efficient and cheaper to produce goods, a far greater variety of products are possible, social norms, medical care, transport, forensics, leisure will all be impacted.  At the same time cybercrime, loss of privacy, psychiatric problems will be expected to impact the society in a negative way.  It might be interesting to project how life might change in the coming decades.  This might be a dodgy exercise as the exponential changes in technologies can create unknown unknowns that are things that we do not even know are possible but suddenly appear to have a major influence. Exponentially increasing technology has already reached a stage that, in many areas, it can improve itself without external human input - this creates a higher growth rate -  called the accelerating growth - characterized by much reduced doubling times.  A consequence of this is that changes that we expect to happen in say 20 years time might happen in 5 years or even much sooner.  Forecasting future becomes very difficult then.    

Historical Perspective:  Past sixty years or so have been critical in terms of the transition from macro- to nano- technologies.  

This transition has gone hand in hand with the understanding of how matter behaves at the atomic and molecular level.  In biological sciences, the understanding of the structure of DNA was the tipping point while in digital technology discovery of the semiconductor transistor triggered the process of device miniaturization.  The following two slides, borrowed from my lecture series on nanotechnology, demonstrate how such transitions have happened:  

The three technologies - nanotech (NT), biotech/genetics (GT) and digital/cyber (DT) - will have profound impact on our future and will determine megatrends that is the subject of this blog.  NT gives us the capability of handling and manipulating matter at atomic and molecular level while DT allows analysis, transfer and storage of large body of data. Active structures of devices in the two technologies operate at the scale of a few nanometers and have gained from a kind of beneficial symbiosis that has enabled their rapid development. DT is largely software-enabled; Micro-electronics and NT provide capability to miniaturize hardware devices.  In not too distant future, the world and what people can do will be increasingly driven by software-enabled devices that will progressively become even smaller.  The scale and speed of the changes driven by exponentially growing technologies will be difficult to absorb by our society.

Biotech/genetics (GT) operates on truly molecular level and derives great benefits from the miniaturization of devices (NT) and superior analytical capabilities afforded by DT. 

In the following, I discuss some of the megatrends driven by the three technologies 
Digital Technology:  DT has already made a big impact on the society.  World Economic Forum (WEF) has looked at megatrends of DT in their 2015 report - this is accompanied by an extensive document.

Let me briefly expand on these megatrends:  Access to the internet is the primary means to communicate and share information.  More and more people are using mobile devices to connect to the internet and this trend should continue.  As devices become smaller, they will be implanted in bodies and serve a host of functions - communication, location and behaviour monitoring, health functions like measuring and sending health related parameters to health centers and automatically releasing healing medicines. In more distant future, implanted devices will be able to communicate unexpressed thoughts or moods by reading brainwaves and other signals. 
Connecting inanimate objects to the internet is a growing trend commonly known as the Internet of Things (IoT). Essentially, many objects in buildings will be connected to the internet - they can exchange their status and be controllable remotely.  For example, the refrigerator in the house can keep track of what is in it and can order items automatically. Or light bulbs may be switched on and off remotely using Wifi.  Homes and offices will become smart.  There is a certain unease about IoT in terms of security.  Legislation is not in place and most companies manufacturing connectable devices have not paid sufficient attention to cyber-security.  In due course it is hoped that this problem will be solved and IoT will become ubiquitous.  
Digitization of Matter (3D printing and creating of physical materials based on digitally transmitted parameters) 

 3D printing allows products to be printed locally and on demand.  Products can be made to personal specifications; e.g. particular shaped foot requires a specialized shoe size.  Bottom-up fabrication will reduce energy costs and waste, will make goods cheaper and generate a lot of creative activity.
The major negative impact of 3D printing will be felt in patent infringements, piracy and product quality.  It will be difficult to control production of offensive weapons etc.
Bio-Printing:   An organ may be printed layer by layer and can be customized in shape, size and even genetically to match the particular requirement.  This will be a game changer in terms of human medical care. For example, the crown for a tooth can be 3D printed to fit exactly or prosthetic body parts.
The negative aspects of bio-printing are to do with ethical concerns.  Also, if any body part may be printed and replaced then there will be little incentive to look after your health.  3D printing will have a serious impact on the way the society operates.
Artificial Intelligence (AI) and Robotics:  The trend here is of computers becoming more intelligent. The situation now is that computers are capable of performing some tasks at a superhuman level while being hopeless in solving anything else.  This is  artificial narrow intelligence (ANI) - we already have robots (which are really just intelligent computers) that perform a host of mostly industrially useful functions. With exponentially increasing technology, computers can achieve artificial general intelligence (AGI) and be as intelligent as humans in a reasonably large number of areas.  AGI will then start to replace humans in many jobs - particularly in services and administrative support.  It is possible that in the next 10-20 years half of the jobs as we have them today will be performed by intelligent machines (robots).  This will create unemployment although alternate jobs will appear in leisure and recreational industries. 

TRANSPORT:  Currently, our transport system is heavily reliant on fossil fuel - this has resulted in increased emission of green house gases (GHG) allegedly responsible for climate change.  A shift from fossil fuel to electric vehicles (EV) is being talked about and in the next 30-40 years most cars on the road might be EVs.  An additional change is that with increasing analytical capabilities of computers and sensors, driverless cars (autonomous vehicles - AV) are also being tested with promising results.  These developments depend largely on our ability to store energy - battery technology - and a range of about 200 miles for EVs is achievable.  The megatrend firmly points to the replacement of fossil fuel powered vehicles to EVs and then to AVs.

Megatrends in Medicine:  

"Doctors are men who prescribe medicines of which they know little, to cure diseases of which they know less, in human beings of whom they know nothing"        ...Voltaire (1694-1778)

The situation has changed dramatically in the past 50 years - it will be fair to say that we now have a good understanding of  the molecular basis of living systems and the causes of disease. The most important development in medicine in recent years has been the understanding of the human genome. Technology now allows mapping 30,000 genes of a human genome for about $1000.  This has opened up the possibility of genomics medicine - the doctor instead of detecting and treating a disease can now focus on predicting and preventing it. 
Based on individual genomic information, the doctor can select a medicine that is active and safe for that person - the specificity will deliver the maximum efficacy in the treatment with minimal side effects. 
Many diseases like sickle cell anemia are caused by a defective gene.  In gene therapy, a new gene is introduced in the genome to replace the defective gene and cure the disease.  Gene therapy will be increasingly used in the future. The newly discovered gene editing technique CRISPR is easier, faster and cheaper than previous methods of modifying DNA at precise locations.  CRISPR will allow permanent modification of genes in living cells and treat genetic causes of disease. 
CRISPR has implications for everything - from treating cancer and other diseases, eradicating genetic malfunctions that cause disease, to increasing crop yields or creating efficient biofuels.  We shall see growing application of CRISPR in the next decade.
Molecular Imaging and Nuclear Medicine:  Until recently, medical diagnostic imaging methods - X-rays, ultrasound and computer aided tomography (CT) - had offered high resolution images of anatomical structures and have been valuable tools.  Molecular imaging provides detailed information of what is happening inside the human body at the molecular and cellular level - it actually tells us how the body is functioning  and measures chemical and biological changes happening in real time.
For an outreach course on medical imaging click here.
Molecular imaging offers unique insights inside of the human body without the need of biopsy or surgery.  It can locate disease like cancers in the earliest stages, often before symptoms occur. 
Molecular imaging includes the field of nuclear medicine which uses very small amounts of radioactive isotopes - radiopharmaceuticals -  to diagnose and treat disease.

Nanotechnology in medicine:  Nanotechnology (NT) 

For an outreach course on nanotechnology click here
For an outreach talk on nano-medicine click here
Nanotechnology is already making serious impact in medicine.  This is because biological systems and their disease work at molecular level.  These were inaccessible  in the past but with nanotechnology, we can now probe and modify them at the molecular level and directly address the problem of diagnosis, detection, drug delivery etc. The current progress is already very impressive:

Megatrends in Nanotechnology:  A nano or nano-meter is one billionth of a meter.  NT is the study, design, synthesis, manipulation and application of materials and devices at nano scale.  NT will create devices with unique properties - devices will be faster, lighter, stronger, more efficient and cheaper.  Materials at nano scale show entirely new phenomenon and properties - nano-particles (NP) have very large surface area and can be millions of time more reactive than macro scale matter.  Additionally, matter at nano scale is largely governed by the laws of quantum physics and behaves very differently from ordinary matter. 

I have described how NT is already having a serious impact on medicine and to some extent on digital technology by reducing device size.  In a more general context, NT will affect all aspects of our life.  Nanoparticles are excellent catalysts, superb lubricants, are used in self-cleaning window glass, suntan lotions, bullet-proof vest, and many other industrial applications - too numerous to list. See also.  NT will make bottom-up manufacturing feasible and reduce waste enormously.  
Miniaturization is driven by NT - we can have nanometer size machines, computer memory chips, sensors of all types.  The megatrend of NT making inroads into the way manufacturing, medical care, communications are performed is firmly established.
FINAL WORD:  Megatrends I have discussed here are not predictions or fiction.  These are trends that are firmly established and will happen over the next few decades. What is not certain and difficult to say is the way the accelerating growth in technology might impact these trends - by making them happen quicker or springing surprises that can make these megatrends obsolete even before they have run theri course.  One thing is for certain - future will be interesting and our civilization will not be prepared for the changes to come.

Physics of Rainbows; Moonbows; Fogbows - All You Need to Know - an Outreach Feature for the Community

Blog Contents and Who am I?

"The rainbow is one of the most beautiful phenomenon in nature. It has inspired art and mythology in all people and (to describe) it has been a pleasure and challenge to mathematical physicists..."  ...Vande Hulst

Rainbow is a bow-shaped display in the sky of the colours of the spectrum, caused by the refraction, reflection and dispersion of the Sun's rays through rain and mist.  ...Colin's English Dictionary 

The first satisfactory explanation of the formation of rainbows was given by Rene Descartes in 1637 based on the laws of reflection and refraction as enunciated by Snell in 1621.  That white light consists of rainbow colours was not known at the time. Isaac Newton subsequently explained the colours of the rainbow. 
Newton's explanation of the colours of the rainbow horrified poet John Keats.  Keats complained that by reducing the rainbow to its prismatic colours, Newton had robbed these marvels of nature of their magic. 

The magical rainbow  -  bright, elusive and heavenly -  is overpowering in its presence and has featured in mythology in all ancient societies.  Without the scientific tools, historic man described the rainbow with awe and inspiration. Rainbows are often portrayed as bridges between people and supernatural beings.  The mythologies developed around the rainbow are absolutely fascinating - I use slides 1 and 2  to describe some of them. You can look at 1, 2, 3 for many more.
The reason I decided to write a blog about rainbows is because, over the years many people have asked me how rainbows happen.  It is a subject people are curious about. The difficulties in explaining how rainbows are formed to somebody with no science background are obvious - I felt that it better to provide a detailed analysis with the basics written down too.  Such an analysis is not available in published literature at one place.  Because the blog is prepared as an outreach piece, I have repeated myself on few occasions  - just to make sure that the pace is not too quick.  Hope this works.  First I list the contents of the blog which are along the lines that people have asked me questions on this topic.

CONTENTS

Rainbows in Mythology

The Primary Rainbow (1st Order Rainbows)

At What Angle in the Sky is a Rainbow Seen?

Background Physics (may be skipped w/o loss of continuity)

Rainbow Formation for a Single Colour

Rainbow Formation with White Light

Why is Red at the Top of the Primary Rainbow?

Why is Sky Brighter Under the Primary Rainbow Arc?

Why is there a Dark Region Between the Rainbows?

The Secondary Rainbow (2nd Order Rainbows)

Rainbows and Water Drop Size

Higher Order Rainbow

Final Word

Click on the slide to view its full page image, press Escape to return to Text

Slide 1:

Slide 2:

The Primary Rainbow

In most cases, we see one rainbow - we call it the primary or 1st order rainbow and it is formed by one internal reflection inside of the raindrops. Standing on solid ground the rainbow we see is part of a circle.  From a high mountain or from a flying plane, sometimes it is possible to see the full circle of the rainbow.  
At times, you can see a second rainbow (secondary rainbow) that is at a higher elevation and is formed by two internal reflections within the raindrops. The two slides show such rainbows in their splendid beauty.
Slide 3:

Slide 4:

At what angle in the sky is a Rainbow seen?   

First we look at rainbow formation for light of one colour - monochromatic light. Myriads of raindrops are formed in rain clouds, and if in another part of the sky the Sun is shining, then parallel rays of sunlight will fall on the raindrops.  If you stand with your back to the Sun then the situation will be as in the diagram - a rainbow is observed when the raindrop deflects the incident rays from the Sun by 138 degrees. 

Slide 5:

Slide 6:

Slides for Background Physics

The science behind the formation, colours and structure  of rainbows requires some background in the way light propagates in different media - air and water in our case. Many of you would be familiar with this science - however, for completeness of description I have included some slides to explain these.  You can miss the next four slides (#7 to 10) - if you are familiar with Snell's laws of reflection and refraction of light.
Slide 7:

 Slide 8:

 Slide 9:

 Slide 10:

Rainbow Formation with a Single Colour  

Light rays of different colours behave differently at the boundary of two media.  First we analyze what happens to a single colour (monochromatic light) and then generalize how different colours disperse to form a rainbow when white light passes through raindrops.
Slide 11 follows the light ray as it enters a raindrop at point A, reflects at the back of the drop at B and then emerges at C in a direction that is different from its original direction.  The deflection angle d depends on the angle of incidence i and the refractive index n; dependence of d on i for water is plotted in slide 12. 
Slide 11:

 Slide 12:

The deviation of the direction of the incident ray passes through a minimum  for an incidence angle of 60 degrees and then d is 138 degrees.  From the figure in slide 12 we also notice that rays for i from about 50 to 70 degrees are bunched around 138 degrees and will emerge from the raindrop along 180-138 = 42 degrees relative to the original rays of light  - this is shown in slide 14.
Slide 13:  

 Slide 14:

Slide 14 shows that a lot more intensity is concentrated around the minimally deviated  ray (number 7 in slide 14) and if you look towards the raindrops along this direction (180 - 138 = 42 degrees) relative to the initial direction of sunlight (antisolar line) then you will notice that the sky is more intense than it is in other directions. As discussed before, the intensity is along a circular arc and is the rainbow you would see.  

Rainbow Formation with White Light

White light consists of a range of colours (see slide 9) - these are separated in the process of refraction because each colour has a different refractive index and bends differently from other colours (see slides 9 and 10).  Each colour ray behaves as monochromatic light and produces its own rainbow.  Slide 15 shows the case for red and violet rays while slide 16 shows the full spectrum. 
Slide 15:

Slide 16:

The colourful light produced by raindrops is received by the eye to perceive the arc of the rainbow.  We notice from slide 16 that in the spectrum red colour rays are deviated the least and should appear at the bottom of the rainbow.  But slide 3 shows that red arc is at the top of the primary rainbow. How?
Why is Red Colour at the Top of the Primary Rainbow?

When we observe a rainbow, our eye is at a fixed position in space and rays of light, whatever colour, must enter our eye for us to perceive them. Slides 17 and 18 show how light rays from different raindrops reach us.

Slide 17:

Slide 18:

Each drop sends a unique colour ray to the eye.  Because violet is deviated more than the red, raindrops generating violet colour are lower in sky than those producing red (see slides 17 and18).  The linear distance of the drops from the eye does not matter, only the angle determines what colour will reach us. That is why we see the colouful arcs of the rainbow with red arc positioned at the top.
Interestingly, raindrops are falling towards the Earth and continuously being replaced by others.  The rainbow we see is generated by new set of raindrops continuously replacing the previous set - it is really unique to the observer and ever-changing.

Why is the Sky Brighter under the Rainbow?
Why is there a Dark Region Between the Rainbows?

Slides 7, 17 and 18 provide a ready explanation why the sky is brighter under the rainbow.
Slide 19:

This is because primary rainbow is formed by one internal reflection of light in raindrops. Slide 7 demonstrated that the rainbow ray is the least deflected ray and raindrops generating these lie at about 42 degrees to the antisolar light. All other rays lie above the rainbow ray and to reach the eye, raindrops must be at a lower elevation than the rainbow arc. This internally reflected light makes the sky under the rainbow arc look brighter.  Slide 7 also shows that the angles that the various rays are travelling cover a wide angular range - this means that light rays of different colours overlap each other and the colour definition is washed out making the sky appear white.
Also little or no light is sent to the eye by raindrops above the primary rainbow arc and the region above the rainbow appears darker (Alexander's dark region). 

The Secondary Rainbow

Primary rainbows are formed by light internally reflecting once inside raindrops.  If the light reflects two times inside a raindrop then the dispersion in constituent colours still happens and the angle of deviation is different.  The rainbow is seen at an elevation of 51 degrees from the antisolar line.  Slide 20 is from hyper-physics website and demonstrates the formation of the secondary rainbow. 
Slide 20:

In secondary rainbows the order of colours is reversed with violet colour at the top of the rainbow.  The secondary rainbow is fainter - only about 10% as intense as the primary -  because it is more spread out and also at each reflection and refraction point, some light intensity is lost.

Rainbows and Water Drop Size

A bow's appearance depends on the size of the raindrops. Raindrops ~ 1 mm diameter produce bright narrow rainbows.  Smaller drops produce duller, broader rainbows.      Raindrops are never exactly identical in size.  Drops greater than 5 mm diameter are not common - as collisions between drops break them up. Surface of bigger drops also oscillates and degrades the sharpness of any rainbows produced by them.
The rainbow description had assumed that drops were spherical; which is certainly correct for drops up to about 0.3 mm diameter.  Larger drops tend to have flattened shapes due to air drag as they fall under earth's gravity. Flattened drops affect the distribution of the brightness in the rainbow arc.
For very small drops, 0.05 mm diameter, different colours start overlapping and the appearance of the rainbow takes a whitish hue.  This happens in fogs and clouds where the rainbows are practically white in colour.  Slide 21 shows a couple of examples of fogbows.
Slide 21:

Higher Order Rainbows

A detailed description of higher order rainbows is given in the August 2016 Review by Professor Haussmann.  We know that the primary (1st order) and secondary (2nd order) rainbows are produced by one and two internal reflections inside raindrops.  There is no reason that three or more internal reflections should not happen and produce the corresponding order rainbows. 

For red light, the calculated minimum deviation of incident rays (the rainbow ray) is as follows (angles in degrees)

Rainbow        Minimum       Rainbow          rainbow

  order            Deviation       Elevation         Angular 

                                                                        Size  

    1                  137.8               42.2                 0.9

    2                  129.3               50.7                 1.7

    3                    41.9             138.1                 2.4

    4                    43.4             136.6                 3.1

    5                  127.9               52.1                 3.7

    6                  148.1               31.9                 4.4

Rainbow Elevation is the direction with respect to the antisolar line that the rainbow should be visible.  We can notice the difficulty in viewing 3rd and 4th order rainbows. They are located in in the backward direction - direction facing the sun, they are also wider and less intense than the 1st and 2nd order rainbows.  5th order rainbow lies just below the 2nd order and is in the Alexander's band (the dark region between the 1st and 2nd order).  This makes the observation of higher order (3 and above) rainbows extremely difficult.
Slide 22:

Recently, however, 3rd and 4th order rainbows have been photographed. I show the only example that I can find in published literature:

Slide 23:

I refer you to Professor Haussmann's review for a detailed discussion of the observation of even higher order rainbows.

Moonbows

If the Moon is bright and similar conditions to normal rainbow formation are present - looking at rain clouds with the Moon shining behind you, then a bow may be observed.  In rare cases, the refracted light in raindrops may be intense enough to make the moonbow visible.
Because moonlight is much weaker than sunlight, a moonbow is not observed very often and the separation of colours is not clearly defined - the moonbow appears whitish. 
On 16th October 2016, we were lucky to have the super-moon light the skies with just the right conditions for observing a bow.  The Moon was bright and even the colours of the spectrum may be inferred in the moonbow.  I have used the following pictures of moonbows from the BBC website - they are truly remarkable photographs.

September 2020: For some beautiful pictures of Moonbows and Aurora together, Click here.

Final Word: Rainbows have been objects of awe and fascination since historic times.  Their vast size and majestic appearance has given rise to many myths and legends.  
How rainbows are produced may be explained at various levels of sophistication - I have provided the simplest description using ray optics.  Wave optics is required to explain the appearance of some dark bands at the edge of a rainbow  - I have considered this to be outside the scope of the present blog. A detailed mathematical description of rainbows may be found in a review (~140 pages) by Adams.
Other good source for rainbows is the Hyperphysics web site.

A nice detailed very readable article on rainbows (with emphasis on why Hawaii has the best rainbows? may be reached here)

I am grateful to Professor Haussmann for some very useful communications about this wonderful subject.

Hope you have enjoyed reading this blog about rainbows.  I would be happy to discuss/explain any questions about this topic.

Parallax - Measuring Distances to Stars; Visual Depth Perception, View from Moving Trains; Locating Virtual Images

  
Parallax is the apparent change in position of an object relative to distant background objects resulting from a change in position of the observer.
Parallax means change and is derived from the Greek word parallaxis.

When traveling in a fast moving train, children often ask questions about the rotating landscape ; the video link demonstrates very well this example of parallax.  

Schematically, the slide (adapted from Wiki) explains how parallax works: 

You can observe parallax if you first view the thumb of your stretched out hand against the objects near the wall with one eye closed. Now viewing the thumb with the other eye will show a shift in its previous position against the background objects. Do try this simple demonstration yourself. 
The two eyes see the thumb in different positions - actually our brain corrects for this change in apparent position as seen by the two eyes to provide one sharp image of the thumb. From this information (parallax), the brain also estimates the distance of the object from us - kind of 3-D perception already built in the processing of images we see with our eyes.  Many birds and insects, do not have much overlap in the fields of view for the two eyes and tend to move their head sideways or up and down to generate depth perception.  (This is called motion-parallax).

We now understand what parallax is - and that it is already useful for depth perception for humans.  What else is it good for?  As it turns out parallax is of fundamental importance in many fields.  I shall look at two in detail here - measuring distances to stars and locating virtual images.

Distances to Stars:  The first step in understanding the Universe is to measure its size - how far stars and galaxies are from the Earth.  Such distances are measured through a series of methods that have overlapping validity - a cosmic distance ladder.  Parallax method is the base rung of the ladder and other methods are calibrated using parallax measured distances as standard.
The distances involved are very large and require a large base line - biggest possible separation between the two points of observation.  The change in viewing direction - parallax angles - also get smaller as the distance to a star increases.  The biggest distance available to us is the diameter of Earth's orbit around the Sun - roughly 300 million kilometers.  The average value of the radius of Earth's orbit is very nearly 150 million km and is called the Astronomical Unit (AU). The following slides explain how distances to stars are determined by the parallax method:

The parallax method defines Parallax Second or parsec or pc as a new unit of distance for astronomy. 

 "A star with a parallax of 1 arcsec has a distance of 1 Parsec (pc). 

One parsec (pc) = 206,265 AU = 3.086 x10¹³ km.

Another unit of distance that is frequently used in astronomy is a Light Year (Ly).  Light travels 300 million km in one second.  

The distance traveled by light in a year is one light year. 

A light year (Ly) = 0.31 pc = 61,270 AU = 0.96 x 10¹³ km.  

For completeness:  1 pc = 3.26 Ly

From the slide, we notice that the distance D in pc to a star is equal to 1AU divided by the parallax p in arcsec.

The parallax angles are generally very small and difficult to measure.  Temperature fluctuations in the atmosphere blur the star view and limit measurements to 0.01 arcsec or 100 pc - no more than 100 stars are in that range. 
Space based telescopes Hipparcos (launched by ESA in 1989) provide a better more accurate measurement of star parallaxes down to 0.001 arcsec or distances to 1000 pc. Hipparcos has measured distances of about 100,000 stars. 1000 pc is still only a small fraction of the Milky way that is 30,000 pc across.
ESA launched Gaia in December 2013 to chart a 3-D map of the Milky Way to reveal the composition, formation and evolution of the Galaxy.  Gaia is designed to measure positions of more than 200 million stars to an accuracy of 0.00001 arcsec (distances to 100,000 pc).
On 13 September 2016, Gaia has published the precise position on the sky and brightness of 1142 million stars.

Locating Virtual Images:  In a somewhat less esoteric application, parallax may be used to locate virtual images formed by mirrors and concave lenses.  Consider the case of a plane mirror - you see your image formed but where is it? How do you pin it down?  We can do it by using parallax.
The slide shows how a virtual image is formed in a plane mirror:  But where is it?

  
In the formation of the virtual image, rays of light from each point do not penetrate the mirror.  They are reflected back to you and appear to come from a point behind the mirror.  Geometrically, using the laws of reflection, it can be shown that the image is exactly the same distance behind the mirror as you are in front of it.  But can we locate it?

We can locate the virtual image using parallax method.  the idea is as follows:

If you view the two pins in the following slide along the line of sight shown then they will appear to overlap.  But on moving the head sideways, they separate in a particular manner that helps you to decide which of the two pins is nearer to you.  

Well,this is essentially what you need to do.  Place a pin at the back of a plane mirror and change its position until the parallax between the pin and the virtual image is removed - they move together as one unit as you move your head sideways.  The position of the pin is the position of the virtual image.
Convex mirrors and concave lenses also form virtual images. These can be located following the same method that I have describe for a plane mirror.

Human DNA Radiation Tolerance is Increased by the Unique Protein in Water Bears (Tardigrade)

In my 2010 lecture on the search for extraterrestrial life, I had discussed how some animals are known to survive extreme conditions of heat, radiation, pressure, vacuum etc. This is important because tolerance of such extreme conditions would indicate that life might have evolved even on planets which are on the periphery of the habitable zones. I reproduce a few slides from my lecture in the following:
  



It is clear that these species have evolved to withstand some of the most inhospitable environments imaginable. 

Tardigrade or Water Bears or moss piglets are one of the hardiest of animals.  They are tiny (0.05 to 1.2 mm long) and live near water. In adverse conditions of extreme hot or cold, very high pressures, space vacuum or intense UV/X-ray radiation water bears shrink, dehydrate and put metabolic activity on hold.  Dehydrated water bears can survive for years but come back to life when in contact with water which they need to grow and reproduce. 

The question is - how do they manage to survive the extreme conditions?  Such unusual tolerance of tardigrades has long fascinated researchers; however, the molecular mechanisms enabling such exceptional tolerance have remained largely unknown.  Water Bears Video
A study of tardigrade genome, published in Nature Communications this week has provided some amazing insight into the tolerance of tardigrade to extreme conditions.
I am reproducing their conclusions in the following slide.  (Apologies for the somewhat formal language of the slide but I feel it presents the researchers' conclusions in a pristine way)

What I find the most exciting is the demonstration that the unique proteins can also protect human cells against X-rays induced DNA damage and improve human tolerance to radiation.  This is a game-changer and as the authors say, there could be a bountiful source of protection genes and mechanisms.  

An interesting question to ask is how did R. varieornatus tardigrade acquire the genes for the unique protein - Hashimoto et al. call the protein Dsup (damage suppressor). 
This has been a controversial issue with some previous work suggesting that tardigrade acquired many of their genes from bacteria through a process called horizontal gene transfer (HGT) - an important mechanism for the evolution of many organisms.  This study - which is by far the most extensive and is a full genome sequence of a tardigrade - sets an upper limit of 1.2% on the contamination by foreign genes and claim that the protein Dsup is uniquely developed by the tardigrade itself.  
It was also demonstrated that Dsup protein affords DNA protection without impairing cell viability and is suitable for application to confer tolerance to other animal cells. 
In fact, Dsup-expressing human cultured cells exhibited better tolerance to 4 Gy of X-ray radiation. (One gray or Gy is the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter).