Things You Probably Didn't Know About Internet Of Things

Devices with embedded sensors and ability to gather and exchange data over an Internet connection are steadily rising in numbers. Everyday objects such as your toaster, refrigerator, car, electric lamp, alarm, wristband, watch etc. can now send and receive data through an Internet portal. By 2025, there could be around 75.44 billion connected devices around the world according to Statista.com. A common Internet of Things platform brings together the data devices send, analyses this data and extracts meaningful information which is then used to trigger meaningful action in a secure manner. This is how Internet of Things work.

What is Internet of Things platform
 
Diverse connected devices or things require a common language to securely communicate with each other. Internet of Things platform is a technology which makes that possible apart from data analytics and derivation of actionable intelligence from the device data. It makes use of cloud technology to securely receive and send data to various connected devices. IoT platform also provides tools for developing applications for IoT hardware. Number of IoT platforms is rising with rising number of IoT devices.

Stats about Internet of Things

Internet of Things or IoT device market could reach 1.1 trillion dollar by 2026.

There could be 3.5 billion cellular IoT connections by 2023.

IoT Market will attract 15 trillion dollar in investments by 2025.

IoT Management market could reach 16.86 billion dollar by 2025.

Global spending on IoT could reach 1.29 trillion dollar by 2020.

IoT Will add 10 - 15 trillion dollar to global GDP by 2030.

75% Of new cars will come with built in IoT connectivity by 2020.

Internet of Things and Cyber-security

IoT technology makes life more convenient but at the same time it is increasing opportunities for hackers and cyber-criminals. Every connected device is a potential target and can become a point of network vulnerability. Cyber-security should be the first thing in mind while purchasing an IoT device. Usually manufacturers don't make their devices secure enough. A not properly secured IoT device could be used by hackers to breach network and hold the entire system for ransom. The increasing number of cyber-attacks is a signal to manufacturers to make their products with advanced security features.

A Use case of Internet of things

You are awaken in the morning by your smart alarm. The smart alarm doesn't just wakes you up, it also signals the coffee maker to start brewing coffee and curtains to fold up. It signals the geyser to turn on, so by the time you enter shower, hot water is ready. The geyser can signal your smart toaster to turn on and electric vehicle to start charging so that by the time you are all set it is ready to take off. Your smart camera senses your absence and signals smart doors to lockup and thermostat to turn off. This is an example of how IoT makes life easy, but it can also be used by hackers to make life difficult, if the security is not competent enough.

References:

1) https://www.ibm.com/blogs/internet-of-things/what-is-the-iot/
2) https://www.iotforall.com/what-is-iot-simple-explanation/
3) https://www.visioncritical.com/blog/internet-of-things-stats
4) https://financesonline.com/iot-statistics/

How Industry 4.0 Is Transforming Industrial Production

A wave of new technologies such as cloud computing, 3d printing, robotics, artificial intelligence and internet of things has brought forth what is widely addressed as the 4th industrial revolution. Industries are using these new technologies to become more productive and efficient. Industry 4.0 is changing the world economy as it enables production of personalized goods closer to market.

IoT and IIoT

Network of interconnected devices is known as internet of things. When each device and machine in an industry is interconnected through a portal, we have what is known as industrial internet of things or IIoT for short. One simple way to achieve IIoT is to provide each device an IP address and then interconnect the devices using this IP address. IIoT makes it possible to get wide range of data for efficient automation and control of plant machinery thus raise productivity while cutting cost.

Cloud Computing and Industry 4.0

Cloud computing makes it possible to access data and computing power from any suitable device with Internet connection. With cloud computing, workers can access information and execute control operations remotely. Cloud solutions make way for faster innovation. Cloud is more secure and saves money.

Artificial Intelligence and Industry 4.0

Machines with artificial intelligence are saving cost and improving production. More and more industries are employing intelligent machines in production lines for higher productivity. Algorithms derive meaningful insight from plant data. This insight is utilized to optimize processes. Machines capable of learning from experience are accomplishing many tasks that previously required human hands. Machines are now capable of facial recognition, natural language processing, obstacle avoidance, autonomous driving, autonomous movement and much more.

3D Printing and Industry 4.0

The process of additively manufacturing a 3d product or component using a 3d printer and a 3d digital model is referred as 3d printing or additive manufacturing. Different type of 3d printers can be used to produce different type of product. For example, a plastic printer can be used to make plastic products and a metal printer can be used to make metallic products. 3D Printing makes it possible to produce highly customized end products. Here is a short list of different types of 3d printers-

1) Fused deposition modeling (FDM)

2) Stereolithography(SLA)

3) Digital Light Processing(DLP)

4) Selective Laser Sintering (SLS)

5) Selective laser melting (SLM)

6) Laminated object manufacturing (LOM)

7) Digital Beam Melting (DBM)

Robotics and Industry 4.0

Robots have become a key element of modern industry. There are collaborative robots that work with humans and there are stand alone robots. Robots have taken over much of the work in a number of fields ranging from automotive to agriculture. AI Powered robots are welding joints, assembling parts and weeding farms. Robots with advanced machine learning algorithms are learning from past mistakes thus becoming more precise and efficient at their tasks.

Engineers are using augmented reality to visualize their designs in 3d, collaborate and communicate better. Industry 4.0 is present and future. With these new technologies industry is aiming to become more autonomous, climate friendly and sustainable, cut cost and waste while raising productivity and efficiency. In future we will see more inclusion of new technologies in production.

References-

1) https://interestingengineering.com/the-industrial-revolution-40-and-its-possibilities-revealed

2) https://www.researchgate.net/profile/Rainer_Schmidt/publication/274894802_Industry_40_-Potentials_for_Creating_Smart_Products_Empirical_Research_Results/links/552beaa00cf21acb091ec04d.pdf

3) http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1807-76922018000400100

4) https://www.seebo.com/industrial-ai/

5) https://proto3000.com/industry-4-0/additive-manufacturing-perspectives-in-industry-4-0/

NASA's WFIRST Mission to Understand Dark Energy and Find Exoplanets

Wide Field Infrared Survey Telescope or ‘WFIRST’ is an infrared space observatory based on a design proposal for ‘Joint Dark Energy Mission’ between ‘Department of Energy’ and NASA. It formally became a NASA mission on Feb 17, 2016. Primary mission time is 6 years during which the mission will collect data for examining expansion history of Universe and growth of large scale structures to assess the effect of Dark Energy. It will also find exoplanets in Milky Way, in order to take forth the survey started by ‘Kepler Mission’. Exoplanets are planets orbiting stars other than our Sun. Exoplanet data will be analyzed for signs of other habitable worlds in Milky Way. Mission is set to be launched in mid 20’s making it NASA’s first space mission dedicated to understanding Dark Energy. It will be second such mission after ESA’s Euclid spacecraft.

‘WFIRST’ will have a 288 Megapixel wide field camera with HgCdTe focal plane array having 110 milliarcsecond pixels, operating in near infrared band (0.7-2.0 micron). Its field of view will be 100 times wider than that of Hubble Infrared Instrument. A grism will be integrated for wide field slitless spectroscopy and for small field spectroscopy it will be using an integral field spectrograph. Grism is a combination of Prism and Grating which allows a central wavelength to pass undeviated. With this wide field instrument, WFIRST will observe distant Supernovae, Weak Gravitational Lensing and Baryon Acoustic Oscillation to obtain data for understanding ‘nature of Dark Energy’.

Mission will also include a custom built, high contrast, advanced stellar Coronagraph for imaging exoplanets directly. It will work in the wavelengths of (0.4-1.0) micrometer and will also provide spectra of planets. Coronagraph, invented by French Astronomer Bernard Lyot in 1939, suppresses starlight using masks, mirror and lenses. It blocks the light from Star while allowing light from surrounding sources to pass, which enables it to see planets which are otherwise not visible due to overwhelming brightness of their host Star. Mission will observe Gravitational Micro Lensing signature of planets which is brief brightening of Stars due to a passing by planet, to detect exoplanets.

WFIRST will be able to look as far as HST with the help of its 2.4m primary mirror Anastigmat Telescope and with its integrated Wide Field Instrument, will have a field of view 100 times wider than HST. Mission will launch on an Evolved Expendable Launch Vehicle or ‘EELV’ from Cape Canaveral to Sun-Earth L2 Halo Orbit with a launch mass of 4166 Kg. Spacecraft will operate in near infrared and visible bands. Data will be transmitted to Earth station in Ka band. Project is managed from Goddard Space Flight Center ‘GSFC’. GSFC also supervises work on system integration, spacecraft bus and wide field instrument. Stellar Coronagraph and Telescope is managed by Jet Propulsion Laboratory ‘JPL’. Space Telescope Science Institute, as a partner, will be concerned with data processing, data analysis and data archiving. Neil Gehrels chairs the Formulation Science Working Group with deputy chairs David Spergel and Jeremy Kasdin. Gehrels is also the Project Scientist and Kasdin the lead scientist for Coronagraph. David Spergel and Jeremy Kasdin are Princeton University professors.

Coronagraph’s ability to provide high contrast images of exoplanets in habitable zone of Planetary Systems is in doubt which has led to discussions on including a Starshade in the mission. Starshade is a giant screen about the size of a baseball field and of the shape of a Sunflower with paper thin petals. This foldable screen can be loaded on a rocket and transported about 50000 km directly ahead of the Telescope, where it can be unfurled and deployed. It works by blocking Starlight and supposed to help in obtaining much higher contrast images of exoplanets than a Coronagraph. Because it can help provide desirable quality images of exoplanets in habitable zone of Planetary Systems, a Starshade is highly desirable by Scientists but the technology is not fully tested and NASA budget cannot support a speedy development right now. In a better scenario, both Coronagraph and Starshade should be in the mission as their function is complementary.  

References:

1) https://wfirst.gsfc.nasa.gov/

2) https://exoplanets.nasa.gov/resources/1015/

3) https://arxiv.org/ftp/arxiv/papers/1411/1411.0313.pdf

Image credits goes to respective sources.              

Amazing Things to Know About ESA's Euclid Dark Universe Mission

     I.        Euclid Dark Universe Mission, named after Greek Mathematician ‘Euclid’, known as Father of Geometry, is first space based mission dedicated to collect data for understanding Dark Matter and Dark Energy, led by European Space Agency, ESA. Euclid spacecraft will look as far back in time as 10 billion years. In Astronomy, it is known as look back time. A Look back time of about 10 billion years is equivalent to observing objects with redshift close to 2. Weak Gravitational Lensing and parameters related to Galaxy Clustering such as redshift, will be measured to infer insight into nature of Dark Matter and Dark Energy.
  

II.        Euclid will operate for 6.25 years after its launch in last quarter of 2020. During that period, it will cover more than a third of extragalactic space which is equivalent to covering more than 15000 deg² of sky, excluding Solar System and Milky Way. The spacecraft will also peer about 10 times deeper, for 3 times during its operation, covering 40 deg² of space for calibration and performance monitoring purposes, during which it will be observing objects with redshift higher than 2, which includes distant Quasars and Galaxies. Euclid will cover about 10 billion objects, measuring weak gravitational lensing of more than 1 billion and redshift of about 50 million of them.

III.    Thales Alenia Space, which is Europe’s largest Satellite manufacturer, headquartered in Cannes, France, is chosen to make the Satellite and its service module. Payload Module and telescope, which includes 1.2 m Silicon Carbide primary mirror, Korsch Telescope, covering an area of 0.5 deg² with a focal length of 24.5 m, will be built by Airbus Defenseand Space. Euclid Consortium which is an International Consortium of Scientists, will make very broad band R+I+Z filter, visible CCD imager- VIS, with pixel size of .1 arcsecond, near infrared, broad band Y,J,H filter Photometer- NISP P and a slitless Spectrograph- NISP S, with common field of view of .53 deg². Data will be collected by the Spacecraft using these instruments and will be sent to Earth at 855 Gbit/s in 4 hr daily slots in K band (25.5-27 Ghz). Onboard storage capacity will be more than 300 GB. The Spacecraft will have an exposure time of up to 4500 sec/field.

IV.   Visible CCD detectors will be a mosaic of 36 (6×6), 4000×4000 pixel each, e2v charge coupled detectors, operating in visible wavelength (550-900 nm). They will be used for measuring shape of Galaxies. Near Infrared detector will be a mosaic of 4×4 Teledyne H2RG detectors, 2000×2000 pixels each, operating in (900-2000) nm wavelengths. It will provide low accuracy redshifts of over a billion galaxies using multicolor photometry and high accuracy redshifts of millions of Galaxies using Spectrometry.

V.      Solar Panels will supply power and provide stability to orientation of telescope. Thermal Insulation will be done to protect against radiation heat. The Spacecraft will weigh 2100 kg and it will be 4.5 m long and 3.1 m in diameter. It will be launched to L2 Sun-Earth Lagrangian point- halo orbit using Soyuz ST-2.1B rocket from Kourou launch site, Guiana Space Center. Travel time to orbit is 30 days.

VI.     Nasa is collaborating with ESA on Euclid Mission. From JPL Lab in Pasadena, California, NASA will put up infrared flight detectors for Euclid science instrument. Goddard Space Flight Center will be used for testing these detectors. Three US science teams totaling 40 scientists are nominated to add to planning and analysis of data.

VII.     Dark Matter is the main contributor to Weak Gravitational Lensing effect of Galaxies as it constitutes most of Galactic matter content. A measurement of bending of light by Galaxies, therefore, gives information about the Dark Matter that it contains. By measuring this effect at this large scale and accuracy, scientists will try to gain additional insight into Physics of Dark Matter. Also, clustering of Galaxies is influenced by Dark Energy. A measurement of clustering is hoped to help in understanding the nature of this mysterious type of Energy.

References:

1) http://sci.esa.int/euclid/

2) https://www.euclid-ec.org/

3) https://arxiv.org/ftp/arxiv/papers/1110/1110.3193.pdf

Image credits goes to respective sources.

Dark Energy and Accelerating Expansion of Universe: Part 2

Click here to go to first part of this article

Supernovae were first explained by Caltech Astrophysicist Fritz Zwicky and his collaborator for few years- Astronomer Walter Baade, in their 1934 paper using recently discovered Neutrons. Term ‘Supernova’ was introduced by them. Zwicky and Baade argued that since Galaxies are extremely distant to one another, Supernovae must be releasing extremely high amount of energy to be observable. It is now known that Supernovae can sometimes be as bright as entire Galaxies for a couple of weeks. Zwicky envisioned that Supernovae will be used to survey Universe at extremely large distances. He found many Supernovae using wide view 18 inch Schmidt Telescope at Caltech’s Palomar Observatory, San Diego County, California, by looking for them during new moon. In total, he found more than 120 of them for which he also used 48 inch Schmidt at Palomar. Around that time, Cepheid variables were used as standard candle at large distances. At even larger distances, Hubble used brightest stars in Galaxies as standard candle, assuming them to be of same size and brightness which was disapproved in following years. In 1952, at Conference of International Astronomical Union in Rome, Walter Baade revealed that he had found two different types of Cepheid Variables in Andromeda galaxy. This called for a revision of Hubble’s earlier estimates in which he had considered, what turned out to be population2 Cepheid variables, as standard candle.

By 1941, Supernovae abbreviated as SNe, were classified into two types. SNe that didn’t have Hydrogen emission lines were called Type1 and those with Hydrogen emission lines were called Type2. By 1985, Type1 SNe were found to be of two subtypes. Type1 with Silicon absorption line at 6150Å were classified as Type1a and those without Silicon absorption line, were classified as Type1b. There is yet another subtype named Type1c. Type1a Supernovae occur when a white dwarf reaches 1.44 Solar mass, accreting matter from its companion star. 1.44 Solar mass limit is known as Chandrasekhar limit in honor of Indian-American Astrophysicist Subrahmanyan Chandrasekhar, who discovered it. Astronomers studied type1a SNe and found that their spectra and light curves were strikingly similar. Swiss Cosmologist Gustav Andreas Tammann and his student Bruno Leibundgut were among the first to notice this similarity. This raised hopes that Type1a can be used as standard candle at large distances. Further detailed study revealed some significant differences in their luminosity and light curve. Mark Phillips of Cerro Tololo Inter-American Observatory, after studying light curve of a number of low redshift Type1a, found that, brighter the Type1a, longer it takes to fade and fainter it is, faster it fades. This observation allowed physicists and Astronomers to know the peak brightness of a type1a with higher precision by observing its light curve- pattern in which it brightens and fades over time and gave them confidence to use type1a as standard candle.  

Supernovae are very rare events, occurring a very small number of times in a Galaxy over a century. Type1a SNe are even more rare. This is why the need for automated search was felt. First robotic Supernova search was attempted by Stirling Auchincloss Colgate in 1970s, without much success. He was a Physicist at Los Alamos National Laboratory and Prof. of Physics at New Mexico tech. His project was a search for early Supernova in Galaxies with a remote controlled telescope in real time using an IBM 360-44 mainframe computer through a digital microwave link from the New Mexico Tech campus to the school’s Langmuir Laboratory. Later in mid 1980’s, Richard A. Muller, Prof. of Physics at UC Berkeley and Carlton R. Pennypacker, Astrophysicist at same institution, started ‘The Berkeley Real Time Supernova Search’ renamed as ‘The Berkeley Automated Supernova Search’. Muller’s group with their robotic telescope, fitted with new CCD detectors and latest computers, identified 20 Supernovae. They were the first to demonstrate the efficiency of automated supernova search. Muller’s graduate student Saul Perlmutter was a leading member of the team. In 1988, the group made a proposal to use their search technique to find distant supernovae. Goal was to measure deceleration parameter q₀ and reveal ultimate fate of Universe using distant Type1a SNe as standard candle. Mass density, expansion history and curvature of Universe was hoped to be found, as well. They faced constant funding problems. In 1991, Muller and Pennypacker handed the leadership to Perlmutter.

In 1986, Danish Astronomer Hans Ulrik Norgaard-Nielsen led a team at La Silla Observatory, Chile, to search for Type1a SNe at large distances. After two years, they only had one Type1a which was already past its peak brightness. This was a dampener for many Astronomers who were hoping to use distant Type1a for measuring cosmological parameters. Berkeley team continued its effort unabated. In 1988 Pennypacker and Perlmutter built a wide field imager for 3.9m Anglo-Australian Telescope at Siding Spring, Australia, to observe thousands of Galaxies in one go. For this they were allocated 12 nights of telescope time to look for distant SNe. Without a convincing search strategy during early years, team had difficulty securing telescope time. They had what is known as catch-22 telescope scheduling problem. They couldn’t get follow up time for obtaining spectra and light curve for a Supernova that may or may not be found and without prescheduled follow up time they couldn’t get time to look for Supernovae. Any search strategy required telescope time to demonstrate its effectiveness. With improved techniques, Berkeley team was successful in identifying its first candidate Supernova in 1992 using Isaac Newton Telescope in La Palma, Canary Islands. This was named SN 1992bi. In 1994, Perlmutter demonstrated that by taking images of adjacent patches of sky containing 10s of thousands of Galaxies just after a new moon and subtracting it from images of same patches of sky taken before next new moon about 29 days later, nearly a dozen new Supernovae could be found as new bright spots. Timing between two new moons ensures that most of the Supernovae found will be still brightening as it takes 21 days for a Type1a to reach peak brightness. After this, scheduling observation time on large telescopes at Keck, Cerro Tololo and Isaac Newton was easy as the team was able to make specific proposals and schedule follow up time with Hubble Space Telescope and other ground based telescopes to confirm findings. At this point the team had grown considerably as prominent Physicists and Astronomers from Institutes around the world joined in. The project was renamed ‘Supernova Cosmology Project’.

More distant SNe have higher redshift than near ones. Therefore same filter cannot be used to measure and compare their brightness to identify the type. Doing so will give incorrect result. This is known as K-correction problem in Astronomy. Light of Supernova is also dimmed by dust and gas in host Galaxy, making it even more difficult to identify their type correctly. SCP Team went about this problem by using correspondingly redshifted filters. By end of 1997, the team had analyzed data for 40 distant Type1a SNe. They found that the SNe were fainter for their redshift than one would expect from a decelerating Universe dominated by matter density. They were fainter, even for an empty Universe, leading them to conclude that expansion of Universe is not decelerating but accelerating. For the acceleration to happen a previously unknown form of energy density should be present in Universe and everyone’s first thought was Einstein’s abandoned cosmological constant, in a somewhat different sense. Cosmologist Michael Turner named it Dark Energy, in analogy with Dark Matter. Perlmutter presented the result first at a press conference sponsored by American Astronomical Society on Jan 8, 1998 in Washington D.C. and then next month in February at UCLA symposium on Dark Matter, in California.                

Having heard about the success of Perlmutter’s team in finding Type1a Supernova at about 5 billion lightyears away in early March of 1994, Nicholas Suntzeff of Texas A&M and Brian Schmidt started talking about forming their own team to compete with Perlmutter’s. Newly formed ‘High Z Supernova search team’ had Suntzeff as its principal investigator. Later in 1996, Schmidt took over the leadership. Another leading member of the team was Adam Riess who was working on his doctoral thesis at the time and whose contributions proved crucial in team’s success. In 1993, Adam had worked with Harvard Prof. William Press on a method to reduce error in measuring Luminosity and distance of Type1a SNe, using data from Calan/Tololo survey. This method was called ‘Light Curve Shape’ method. Later, Adam improved this method by making use of filters of different color to reduce error caused by intervening dust. This new method was called ‘Multicolor Light Curve Shape’ method or MLCS for short. With the help of further improved MLCS, number of Type1a SNe required to make reliable calculation of expansion rate of Universe was greatly reduced. This helped in catching up with SCP team. Brian Schmidt wrote software required for automated calculations and was the one to find, team’s first high z Type1a.  

By February 1998, the team had analyzed 16 high redshift Type1a SNe. Their calculations showed a negative matter density which couldn’t be possible. After working out the possibility of overlooked error, only logical conclusion was a negative deceleration parameter, which means an accelerating Universe. Their data was showing the same result as SCP team’s data. Supernovae were too faint for what would be expected from a decelerating Universe. Prof. Alex Filippenko of UC Berkeley, who had done most of the spectroscopic work for measuring redshifts, made the announcement at UCLA Symposium on Dark Matter in California in February 1998. Formal submission of result to ‘The Astronomical Journal’ came on March 13, 1998, in a paper titled ‘Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant’. High Z team was several months early than SCP team in formally publishing their result. Perlmutter, Schmidt and Riess were awarded The 2006 Shaw Prize in Astronomy. In 2011, they were awarded The Nobel Prize in Physics, which they split among their team members, making it clear that everyone's contribution was important in the discovery.

Members of both team continued to find SNe at even higher redshift. A new ‘Higher Z’ team was formed by including some new members with some members of old High Z team. Goal was to plot the expansion history of Universe using Type1a SNe that exploded when Universe was young. A comparison of change in redshift of these SNe with change in redshift of more nearby SNe, would effectively give clues about expansion history of Universe. By using the improved Hubble Space Telescope, they found 6 Type1a at redshift greater than 1.25, between 2002 and 2003. Data analysis showed that Universe was decelerating early on but after reaching a particular size during its decelerating expansion phase, started accelerating. A simple explanation is that- matter density dominated in early Universe, but with increasing size it grew weaker against Dark Energy density. Acceleration phase started when Dark Energy density started dominating the weakening matter density. In 2007, with new data from 23 Type1a SNe, this conclusion was confirmed by the ‘Higher Z’ team. This data also indicated that property of Dark Energy didn’t change over time. Another conclusion which came from data is- Density of Dark Energy doesn’t dilute with expanding space, which means, we are living in a Universe which will accelerate forever, taking Galaxies away from each other, ever faster.

Meanwhile Perlmutter and others have been promoting space based Supernova/Acceleration Probe Mission or ‘SNAP’ for getting better data to work with. This mission is now superseded by Widefield Infrared Survey Telescope Mission or ‘WFIRST’. Budget overruns on JWST mission has pushed dates for any Satellite mission for Dark Energy studies to mid 20’s. Ongoing Dark Energy Survey at Cerro Tololo Inter-American Observatory is supposed to provide valuable insight into nature of Dark Energy. European Space Agency is going ahead with ‘Euclid Dark Universe Mission’, which is expected to launch in December 2020. This spacecraft will map 2 billion Galaxies across more than a third of sky providing Astronomers with wealth of data to analyze. A new study by Adam Riess and his team using HST with its wide field camera 3 is indicating that Dark Energy may be growing in strength. Newly measured, expansion rate of Universe is giving a value which is about (5-9)% faster than what is measured from CMB data. They have submitted their paper about this study to arXiv on 5 Apr, 2016. The study will also appear in ‘The Astrophysical Journal’.

Theorists are hard at work trying to figure out Dark Energy. It has been put forth that Dark Energy is a property of space itself and doesn’t dilutes with its expansion and time for Universe to double in size remains same. But that line of thought now seems in jeopardy with the release of recent measurements by Riess and his team. Universe should double in size in about 9.8 billion years, according to these new measurements.

References:

1) http://adsbit.harvard.edu//full/2005ASPC..342...53K/0000053.000.html

2) http://www.astro.princeton.edu/~burrows/pub-html/papers/pnas201422666_7rt2gl.pdf

3) https://arxiv.org/pdf/astro-ph/9812133

4) https://arxiv.org/pdf/astro-ph/9805201.pdf

5) https://www.nobelprize.org/nobel_prizes/physics/laureates/2011/popular-physicsprize2011.pdf

Image credits goes to respective sources.          

Dark Energy and Accelerating Expansion of Universe

Cepheid variables are stars whose luminosity/brightness increases and reduces with time. 18^th century Astronomers were well aware of such stars. In 1893, Harvard Astronomer Edward Charles Pickering (Jul 19, 1846-Feb 3, 1919) recruited a recent grad of ‘Radcliffe College’ then called- ‘the society for the collegiate instruction for women’ to work as a ‘human computer’ to analyze photographic plate collection of Harvard College Observatory to study these stars with variable brightness/luminosity. She was Henrietta Swan Leavitt (Jul 4, 1868 – Dec 12, 1921), daughter of a congregational church minister. While observing those plates, she noticed a pattern in some of variables. Brighter variables appeared to have longer periods than less bright ones. Leavitt used the method of trigonometric parallax to calculate distance to these Cepheids located in small and large Magellanic Clouds. She assumed all Cepheids in a Magellanic Cloud to be at same distance from Earth. With these distances she was able to calculate the maximum luminosity of stars from their observed apparent brightness or apparent magnitude in photographic plates using inverse square law.

B = L/(4πd²)

Where, B= Brightness of star measured using magnitude scale

           L= Luminosity or energy output of star per unit time also known as

                intrinsic brightness of the star measured in Suns

           d= Distance from the star

Also, apparent magnitude m and absolute magnitude M can be linked as

M = m + 5 - 5logd

Where, d= Distance from star

           Apparent magnitude m= Brightness as observed through telescope      without atmospheric interference.

           Absolute magnitude M= Apparent brightness of star at 10 parsec from

                                              observer.

A star’s luminosity in Suns can be linked to its absolute magnitude M as

logL = -0.4M + 1.884

In Astronomy, Brightness is measured using a calibrated magnitude scale first created by Greek Astronomer Hipparchus in around 130-120 BC. SI Unit for apparent brightness is W/m² and is defined as measure of amount of energy coming from a star per unit area per unit time to Earth. Magnitude of two stars and their brightness b₁ and b₂ can be linked as

b₁/b₂ = 10^(2/5)(m2-m1)

When she plotted luminosity against period of each variable, the pattern was noticeable. Period of these variable stars was directly proportional to their maximum luminosity. She analyzed 1777 of these variables to come to her conclusion and published her result in ‘Annals of the Astronomical Observatory of Harvard College’ in 1908 titled ‘1777 Variables in the Magellanic Clouds’. After further study she gave confirmation to her initial conclusion in 1912. As Leavitt put it- “A straight line can readily be drawn among each of the two series of points corresponding to maxima and minima, thus showing that there is a simple relation between the brightness of the variables and their periods”. Leavitt’s plot is known as ‘period luminosity relationship’ or ‘Leavitt’s law’ and is used by Astronomers to determine absolute brightness/luminosity/magnitude of Cepheid, having obtained its period through telescopic observation.

Trigonometric Parallax method can be used to determine distance to stars which are up to 200 parsec or 650 light-years away. In this method, position of a nearby star is obtained either visually or photographically with respect to a background star further away. 6 months later, when Earth is at diagonally opposite point in its orbit around sun, position is obtained again. If the angle between the two lines of sight is 2p, distance of the star from sun is ‘d’ and distance between Earth and Sun                                                        is ‘r’, then

Tanp = r/d

From this,

d = r/(Tanp)

Distance of star from Earth will be

D = √(r² + d²)

Here, p = parallax

         r = 149 million km.

Parallax is a very small angle and is usually measured in seconds of arc. A star with parallax of 1 second of arc as observed from Earth is said to be at 1 parsec from Sun. 1 Second of arc or 1 arcsecond is 1/3600 of a degree. A parsec is equal to 3.0857×10¹³ km or about 19 trillion miles. Astronomical unit is distance between Earth and Sun and equals to about 149,597,870,700 meters. Yet another unit is a lightyear which is the distance light travels in a year and equals to 9.4607×10¹² km or about 6 million million miles. A parsec is about 3.26 lightyears in length. Appropriate unit is used in case of small and large distances.

Hipparchus classified stars he could see in night sky according to their visual brightness. He assigned a magnitude of 1 to the brightest stars and magnitude 6 to least bright ones. Ptolemy refined Hipparchus system in 140AD. This magnitude scale is still in use having modernized and improved from time to time. Galileo using his telescope introduced seventh magnitude star. In 1856, Oxford Astronomer Norman Robert Pogson (Mar 23, 1829-Jun 23, 1891) set first magnitude star to be 100 times as bright as sixth magnitude and established the logarithmic magnitude scale. In Pogson’s scheme, difference of one magnitude is same as brightness difference of (100)^1/5 which is 2.512- known as Pogson’s ratio. Pogson’s scale assigned Polaris a magnitude of 2. It was used as zero point of the scale. Later, on discovering that Polaris is slightly variable, Vega was used as standard reference with an assigned magnitude of 0, a standard still in use. Stars brighter than Vega are assigned negative magnitudes. Hubble space telescope could see stars up to a magnitude of 31. In late 19^th century, after the introduction of photography in stellar photometry, Astronomers found that some stars appearing similar in brightness to eye were differing on photographic plates. It was happening because photographic emulsions used on photographic plates were more sensitive to blue light than red. This led to the creation of photographic magnitudes denoted as m_p whereas visual magnitudes are denoted as m_v. Henrietta Swan Leavitt analyzed 299 plates from 13 telescopes to construct her logarithmic scale, spanning 17 magnitudes. Difference between star’s photographic and visual magnitudes is called ‘color index’ which is a measure of star’s color. Color index of blue stars came to be of negative value while that of yellow, orange and red stars is increasingly positive. Now days, magnitude is obtained using standard photoelectric photometer through standard color filters, most common of which is UBV. U stands for near ultraviolet filter, B stands for Blue filter and V stands for visual band filter. Color index is obtained by subtracting V magnitude from B magnitude. This way the color index of yellow sun came to be 0.63. UBV system was extended to red and near infrared filters, becoming UBVRI system. System was extended beyond infrared to J, K, L, N, Q bands. An object’s real brightness is known as its bolometric magnitude m_bol which is a measure of total radiation the object is emitting. Modern Photometry makes use of CCD sensors. CCD stands for charge coupled devices. CCD Sensors can receive more than 95% of incoming light. 

Spectrum is obtained when stellar light is shown through a prism. Prism or a diffraction grating splits light into its constituents. Continuous spectrum is obtained when there is no intervening matter between the light source and prism or diffraction grating. When dust or gas cloud is heated by a proto star or active galactic nucleus, Electrons of their atoms absorb specific amount of energy and emit it in specific quantas. Such re emitted radiation when passes through prism gives of a particular type of spectrum known as emission spectrum, having bright lines corresponding to specific wavelengths depending upon type of atom that emitted the radiation. By comparing such stellar spectrum with spectrum of known elements, composition of stellar dust or gas is known. When radiation of a star is absorbed by electrons in the atoms of surrounding colder dust or gas, it gets re radiated with somewhat reduced intensity and in random direction. When such re radiated light passes through prism it gives of absorption spectrum which is a continuous spectrum except for dark lines at wavelengths where elements in dust or gas would have their bright emission lines. Therefore such spectra can also be used to obtain elemental composition of intervening dust or gas. Helium line was discovered in 1868 in solar spectra independently by Norman Lockyer and Pierre Janssen and was found on Earth in 1895. Modern Spectroscopy makes use of Holographic gratings and gratings made using Lithographic techniques. Reactive Ion Etching is another advanced method in use now for making gratings. 
     

Click here to read The Dark Matter Story to know more about measuring wavelengths and redshifts

By the year 1913, Edwin Powell Hubble (Nov 20, 1889 – Sep 28, 1953) was sure that he wanted to get into Astronomy. He gave up law practice and went back to his alma mater- the University of Chicago, to get doctorate in Astronomy. While finishing his doctoral work in early 1917, he was invited by George Ellery Hale to work with recently finished 100 inch telescope at Mount Wilson observatory, Pasadena, California. Hubble accepted the commission as an army captain instead. After war, he joined Mount Wilson Observatory in summer of 1919. Hubble was well aware of spectroscopic work done by Vesto Melvin Slipher (Nov 11, 1875 – Nov 8, 1969) at Lowell Observatory in Arizona and his 1912 discovery of shifts in spectral lines toward red band indicating that most of the nebulae are moving away from us. Also, Slipher was first to observe the rotation of spiral Galaxies in 1914. General consensus among Physicists of those days was that the Universe is static. Even Albert Einstein (Mar 14, 1879-Apr 18, 1955) believed that Universe is unmoving which led him to introduce cosmological constant in his field equation of General Relativity to exactly balance out the crunching effect of gravity which he thought would cause the Universe to collapse on itself. General relativity showed how stress-energy causes spacetime to curve. His equations in their original form indicated an expanding or shrinking Universe which Einstein couldn’t believe.

Nebulae, which later became known as Galaxies were the great mystery of those days. They appeared as fuzzy patches in those old telescopes and were subject of great debate between Harlow Shapley and Heber Curtis in 1920. Shapley believed that the Milky Way is 300,000 lightyears wide and is our entire Universe, Sun is not at center and Nebulae are part of Milky Way system. Curtis argued that Milky Way is only 30,000 lightyears across and Nebulae are Island Universes, separate Galaxies beyond Milky Way. Hubble was interested in studying these Nebulae and so he started taking photographic plates of these objects. On the night of Oct 5, 1923, he observed 3 Novae close to Andromeda Nebula- M31. On comparing this plate with earlier plates, he noticed that one of the Novae is actually a variable star. Further observations confirmed that the variable star matches characteristic of a Cepheid variable. Using the period luminosity graph for Cepheids, Hubble was able to calculate distance to the variable star and got a value of about 900,000 lightyears for distance of Andromeda Nebula. The actual value is close to 2.2 million lightyears. Earlier, Harlow Shapley had found a value close to 300,000 lightyears for the diameter of Milky Way, current value being 100,000-120,000 lightyears. This conveniently put M31 well beyond the boundaries of Milky Way and therefore Heber Curtis’s point of view was partially confirmed that M31 and other such Nebulae are separate star systems comparable to Milky Way. Hubble published his discovery first in Nov 23, 1924 issue of New York Times and then in front of American Astronomical Society on Jan1, 1925.

Hubble continued his work on Nebulae, calculating distance to 22 Nebulae. He also calculated their velocities using shifts in their spectral lines, 4 of which were determined by his assistant Milton Lasalle Humason. He further calculated distance to 22 more Nebulae from their radial velocities, assisted by Humason. Observing the photographic plates, Hubble could see that small appearing Nebulae have greater radial velocities than bigger ones. Assuming that all Nebulae are more or less the same size, he concluded that more distant Nebulae are moving at much greater velocities than the nearer ones. Together with 2 earlier estimates by Harlow Shapley, he had data for total 46 Nebulae. He plotted the radial velocities corrected for solar motion against distance calculated using luminosities for 24 Nebulae and also for the 22 Nebulae whose distance could not be calculated individually. He found an almost linear variation in radial velocity with distance. This indicated that with increasing distance the radial velocity of Nebulae also increases by a common factor, a term which later became known as Hubble Constant. Hubble concluded that Nebulae are going away from each other and the Universe is expanding. He communicated these results in his Jan 17, 1929 paper titled ‘A Relation Between Distance and Radial Velocity Among Extra Galactic Nebulae’. The relation can be mathematically expressed as,

v = H₀×d

This is known as Hubble’s law, where,

v = recessional velocity of Galaxy

d = Distance to the Galaxy

H₀ = Hubble’s constant    

Hubble got a value of about 500 km/s/Mpc for his proportionality constant, current value being 67.8±0.77 km/s/Mpc which means that expansion of Universe increases by about 67.8 km/s for every 3.26 million lightyears in any direction.

In 1917, Albert Einstein introduced cosmological constant to curvature side of his field equation of Gravitation to make the equations predict a static Universe as a dynamic Universe was considered absurd at that time. Russian Physicist Alexander Friedmann (Jun 16, 1888-Sep 16, 1925), worked on Einstein’s field equations without presumptions and showed that Universe might be expanding at a rate which can be calculated using the equations. Friedmann’s equation can be obtained by putting metric for homogeneous and isotropic Universe in Einstein field equations. He presented his equations in 1922. Georges Lemaître (Jul 17, 1894-Jun 20, 1966), a Belgian priest and astronomer, found something similar from Einstein’s field equations in 1927. Lemaître made the first empirical determination of Hubble constant H₀ using these equations. He also suggested that if Universe is expanding then it must have been unimaginably small back in time, a state he called ‘cosmic egg’. He met Einstein and showed his results to him. Einstein held on to the popular belief of a static Universe and disapproved Lemaître’s result. After Hubble published his findings in 1929, Einstein visited him. He saw the data and was convinced that the Universe is expanding. He then dropped cosmological constant, restoring the field equations to their original form.    

After Hubble, almost everyone accepted an expanding Universe. Astronomers and Physicists believed that the expansion must be slowing down due to gravitational pull of matter-energy density. Rate of slowdown was named deceleration parameter with symbol q₀. Allan Rex Sandage (Jun 18, 1926 – Nov 13, 2010), a student of Walter Baade and Hubble, published a paper in 1961 titled ‘The Ability of the 200 inch Telescope to Discriminate Between Selected World Models’. In this paper he advocated that cosmology is search for two parameters- Hubble constant H₀ and deceleration parameter q₀. Earlier in 1958 he had measured Hubble constant to be 75 km/s/Mpc, which is its first good estimate.

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References:

1)https://www.famousscientists.org/henrietta-swan-leavitt/

2)https://apod.nasa.gov/debate/debate20.html

3)http://www.amnh.org/explore/resource-collections/cosmic-horizons/profile-georges-lemaitre-father-of-the-big-bang/

4)http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp

5)http://w.astro.berkeley.edu/~mwhite/darkmatter/hubble.html

Image credits goes to respective sources.