Minute Physics: Real World Telekinesis

How do magnets affect things at a distance? How does the Sun heat our planet from 93 million miles away? How can we send messages across the world with our cell phones? We take these seemingly simple things for granted, but in fact there was a time not too long ago when the processes behind them were poorly understood, if at all… and, to the uninformed, there could seem to be a certain sense of “magic” about them.

This video from MinutePhysics, featuring director of the Perimeter Institute for Theoretical Physics Neil Turok, illustrates how our understanding of electromagnetic fields was developed and why there’s nothing magic about it… except, perhaps, how they pack all that excellent info into 5 minutes. Enjoy!

Video: MinutePhysics (Created by Henry Reich.) In conjunction with The CBC Massey Lectures.

Is There Life on Earth?


It may seem like a silly question — of course there’s life on Earth — but what if we didn’t know that? What if we were looking at Earth from another vantage point, from another planet in another star system, perhaps? Would we be able to discern then if Earth were in fact teeming with life? All we’d have to go on would be the tiniest bit of light reflected off Earth, nearly lost in the intense glare of the Sun.

Researchers have found that the secret is knowing what kind of light to look for. And they discovered this with a little help from the Moon.

How Earthshine works. (ESO/L. Calçada)

By using Earthshine — sunlight light reflected off Earth onto the Moon — astronomers with the European Southern Observatory have been able to discern variations that correlate with identifying factors of our planet as being a happy home for life.

In observations made with ESO’s Very Large Telescope (VLT), the presence of oceans, clouds, atmospheric gases and even plants could be detected in the reflected Earthshine.

The breakthrough method was the use of spectropolarimetry, which measures polarized light reflected from Earth. Like polarized sunglasses are able to filter out reflected glare to allow you to see clearer, spectropolarimetry can focus on light reflected off a planet, allowing scientists to more clearly identify important biological signatures.

“The light from a distant exoplanet is overwhelmed by the glare of the host star, so it’s very difficult to analyze — a bit like trying to study a grain of dust beside a powerful light bulb,” said Stefano Bagnulo of the Armagh Observatory, Northern Ireland, and co-author of the study. “But the light reflected by a planet is polarized, while the light from the host star is not. So polarimetric techniques help us to pick out the faint reflected light of an exoplanet from the dazzling starlight.”

Since we have fairly reliable proof that life does in fact exist on Earth, this provides astronomers with a process and a benchmark for locating evidence of life on other distant worlds — life as we know it, anyway.

Read more on the ESO website here.

Main image credit: ESO/B. Tafreshi/TWAN (twanight.org). This research was presented in a paper, “Biosignatures as revealed by spectropolarimetry of Earthshine”, by M. Sterzik et al. to appear in the journal Nature on 1st March 2012. The team is composed of Michael F. Sterzik (ESO, Chile), Stefano Bagnulo (Armagh Observatory, Northern Ireland, UK) and Enric Palle (Instituto de Astrofisica de Canarias, Tenerife, Spain).

Dispersion of Light

Dispersion of Light

Look up into the rainy sky! What do you see? Well, if its just rained and the sun is once again shining, chances are you see a rainbow. Always a lovely sight isn’t it? But why is it that after a rainstorm, the air seems to catch the light in just the right way to produce this magnificent natural phenomenon? Much like stars, galaxies, and the flight of a bumblebee, some complicated physics underlie this beautiful act of nature. For starters, this effect, where light is broken into the visible spectrum of colors, is known as the Dispersion of Light. Another name for it is the prismatic effect, since the effect is the same as if one looked at light through a prism.

To put it simply, light is transmitted on several different frequencies or wavelengths. What we know as “color” is in reality the visible wavelengths of light, all of which travel at different speeds through different media. In other words, light moves at different speed through the vacuum of space than it does through air, water, glass or crystal. And when it comes into contact with a different medium, the different color wavelengths are refracted at different angles. Those frequencies which travel faster are refracted at a lower angle while those that travel slower are refracted at a sharper angle. In other words, they are dispersed based on their frequency and wavelength, as well as the materials Index of Refraction (i.e. how sharply it refracts light).

The overall effect of this – different frequencies of light being refracted at different angles as they pass through a medium – is that they appear as a spectrum of color to the naked eye. In the case of the rainbow, this occurs as a result of light passing through air that is saturated with water. Sunlight is often referred to as “white light” since it is a combination of all the visible colors. However, when the light strikes the water molecules, which have a stronger index of refraction than air, it disperses into the visible spectrum, thus creating the illusion of a colored arc in the sky.

Now consider a window pane and a prism. When light passes through glass that has parallel sides, the light will return in the same direction that it entered the material. But if the material is shaped like a prism, the angles for each color will be exaggerated, and the colors will be displayed as a spectrum of light. Red, since it has the longest wavelength (700 nanometers) appears at the top of the spectrum, being refracted the least. It is followed shortly thereafter by Orange, Yellow, Green, Blue, Indigo and Violet (or ROY G. GIV, as some like to say). These colors, it should be noted, do not appear as perfectly distinct, but blend at the edges. It is only through ongoing experimentation and measurement that scientists were able to determine the distinct colors and their particular frequencies/wavelengths.

We have written many articles about dispersion of light for Universe Today. Here’s an article about the refractor telescope, and here’s an article about visible light.

If you’d like more info on the dispersion of light, check out these articles:
dispersion of Light by Prisms
Q & A: Dispersion of Light

We’ve also recorded an episode of Astronomy Cast all about the Hubble Space Telescope. Listen here, Episode 88: The Hubble Space Telescope.


Diffraction of Light

Diffraction of Light

For some time, the behavior of light has baffled scientists. Initially, and in accordance with classic physics, light was thought to be a wave, an indefinable form of energy that simply flowed from a heated source. However, with the advent of quantum physics, scientists came to realize that photons, a tiny elementary particle responsible for all forms of electromagnetic radiation, was in fact the source. So you can imagine how confounded they were when, in the course of performing experiments, they discovered that it exhibited the behavior of both a particle and a wave! This rather unique behavior, the ability of light to behave as a wave, even though it is made up of tiny particles, is known as the Diffraction of Light.

By definition, diffraction refers to the apparent bending of waves around small obstacles and the spreading out of waves past small openings. It had long been understood that this is what happens when a wave encounters an obstacle, and by the 17th and 18th centuries, this behavior was observed through experiments involving light. One such physicist who observed this at work was Thomas Young (1773 – 1829), an English polymath who is credited devised the double-slit experiment. In this experiment, Young shone a monochromatic light source (i.e. light of a single color) through an aperture (in this case, a wall with a horizontal slits cut in it) and measured the results on a screen located on the other side. The results were interesting, to say the least. Instead of appearing in the same relative shape as the aperture, the light appeared to be diffracting, implying that it was made up of waves. The experiment was even more interesting when a second slit was cut into the screen (hence the name double-slit). Young, and those who repeated the experiment, found that interference waves resulted, meaning that two propagation waves occurred which then began to interfere with one another.

A more common example comes to us in the form of shadows. Ever notice how the outer edges do not appear solid, but slightly fuzzy instead? This occurs as a result of light bending slightly as it passes around the edge of an object, again, consistent with the behavior of a wave. Similar effects occur when light waves travel through a medium with a varying refractive index, resulting in a spectrum of color or a distorted image. Since all physical objects have wave-like properties at the atomic level, diffraction can be studied in accordance with the principles of quantum mechanics.

We have written many articles about diffraction of light for Universe Today. Here’s an article about visible light, and here’s an article about telescope resolution.

If you’d like more info on diffraction of light, check out these articles:
The Physics of Light: Diffraction
Experiments on Diffraction of Light

We’ve also recorded an episode of Astronomy Cast all about the Hubble Space Telescope. Listen here, Episode 88: The Hubble Space Telescope.


Absorption of Light

Absorption of Light

Those who can remember sitting through elementary science class might recall learning that with all matter, light is absorbed and converted into energy. In the case of plants, this process is known as photosynthesis. However, they are by no means the only species or objects that do this. In truth, all objects, living or inorganic are capable of absorbing light. In all cases, absorption depends on the electromagnetic frequency of the light being transmitted (i.e. the color) and the nature of the atoms of the object. If they are complementary, light will be absorbed; if they are not, then the light will be reflected or transmitted. In most cases, these processes occur simultaneously and to varying degrees, since light is usually transmitted at various frequencies. Therefore most objects will selectively absorb light while also transmitting and/or reflecting some of it. Wherever absorption occurs, heat energy is generated.

As already noted, absorption depends upon the state of an objects electrons. All electrons are known to vibrate at specific frequencies, what is commonly known as their natural frequency. When light, in the form of photons, interacts with an atom with the same natural frequency, the electrons of that atom will become excited and set into a natural vibrational motion. During this vibration, the electrons of the atom interact with neighboring atoms in such a way as to convert this vibrational energy into thermal energy. Subsequently, the light energy is not to be seen again, hence why absorption is differentiated from reflection and transmission. And since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light.

By relying on this method, physicists are able to determine the properties and material composition of an object by seeing which frequencies of light it is able to absorb. Whereas some materials are opaque to some wavelengths of light, they transparent to others. Wood, for example, is opaque to all forms of visible light. Glass and water, on the other hand, are opaque to ultraviolet light, but transparent to visible light.

Ultimately, absorption of electromagnetic radiation requires the generation of the opposite field, in other words, the field which has the opposite coefficient in the same mode. A good demonstration of this is color. If a material or matter absorbs light of certain wavelengths (or colors) of the spectrum, an observer will not see these colors in the reflected light. On the other hand if certain wavelengths of colors are reflected from the material, an observer will see them and see the material in those colors. For example, the leaves of green plants contain a pigment called chlorophyll, which absorbs the blue and red colors of the spectrum and reflects the green. Leaves therefore appear green, whereas reflected light often appears to the naked eye to be refracted into several colors of the spectrum (i.e. a rainbow effect).

We have written many articles about the absorption of light for Universe Today. Here’s an article about absorption spectra, and here’s an article about absorption spectroscopy.

If you’d like more info on light absorption, check out an article about Light Absorption, Reflection, and Transmission. Also, here’s an article about reflection and absorption of light.

We’ve also recorded an entire episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.


What Is Light Energy

Lighting Up the Night


Just asking ‘what is light energy’ opens you up to a flood of other questions trying to narrow down the context that you are asking the question in. In photometry, luminous energy is the perceived energy of light. It can also be defined as the electromagnetic radiation of visible light. Since light itself is energy, then another definition is relevant: light is nature’s way of transferring energy through space.

The speed of light is about 300,000 km/s. To put that in perspective, when you watch the sun set, it has actually been 10 minutes since that light left the Sun. Light energy is measured with two main sets of units: radiometry measures light power at all wavelengths and photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception. Photometry is useful when measuring light intended for human use. The photometry units are different from most units because they take into account how the human eye responds to light. Based on this, two light sources which produce the same intensity of visible light do not necessarily appear equally bright.

Light exerts a physical pressure on objects in its path. This is explained by the particle nature of light in which photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by the speed of light. The effect of light pressure is negligible for everyday objects. For example, you can lift a coin with laser pointers, but it would take 1 billion of them to do it. Light pressure can cause asteroids to spin faster by working on them like wind pushing a windmill. That is why some scientist are researching solar sails to propel intersteller flight.

Light is all around us. It has the ability to tan or burn our skins, it can be harnessed to melt metals, or heat our food. Light energy posed a huge challenge for scientist up to the 1950’s. Hopefully, in the future, we will be able to use light energy and solar wind to travel among the stars.

We have written many articles about light energy for Universe Today. Here’s an article about the prescription for light pollution, and here’s an article about where visible light come from.

If you’d like more info on Light Energy, check out NASA’s Page on Atoms and Light Energy. And here’s a link to an article about How Photovoltaics Work.

We’ve also recorded an episode of Astronomy Cast all about Energy Levels and Spectra. Listen here, Episode 139: Energy Levels and Spectra.

Johns Hopkins University

Light Spectrum

Light spectrum can mean the visible spectrum, the range of wavelengths of electromagnetic radiation which our eyes are sensitive to … or it can mean a plot (or chart or graph) of the intensity of light vs its wavelength (or, sometimes, its frequency). More possible ambiguity: ‘light’ … which can refer to what we see, or to the part of the electromagnetic spectrum that optical telescopes (especially the ones down here on the ground) work in (and sometimes, just occasionally, it means the whole of the electromagnetic spectrum, or any electromagnetic radiation). Good news: the context makes it clear!

The realization that visible light is made up of colors is most often attributed to Isaac Newton (though a strong case can be made that it was known well before him), who used a prism to create a spectrum (rainbow of colors) from a beam of white light, and another to recombine them back into white light. And what’s it called when you spread light into a spectrum, for the purpose of studying it (in astronomy, chemistry, …)? Spectroscopy. And is there a different word if it’s infrared, ultraviolet, x-rays, … which are spread into a spectrum (rather than visible light)? Nope, it’s still spectroscopy.

Visible light ranges from about 380 nanometers (nm) to about 750 nm (or, as is still common in astronomy, ~3800 angstroms (Å) to ~7500 Å); the window in the Earth’s atmosphere which allows us to do astronomy from down here on its surface (and lets the light of the Sun through, so we can see!) is a bit wider than the visible spectrum; it goes from about 300 nm to about 1100 nm (or 1.1 µ).

To an astronomer, a light spectrum has two main components, the continuum and the lines (sometimes bands as well). The lines are discrete wavelengths (well, they do have some ‘width’, hence ‘narrow lines’ and ‘broad lines’), either emission or absorption, and correspond to a particular atomic transition (an electron jumps between one allowed energy level in an atom, or ion, and another; bands are the same thing, except for molecules … and the allowed states are either vibrational or rotational). And the continuum? Well, it’s the part that isn’t lines! It varies smoothly, and generally slowly, across the spectrum.

Spectroscopy – analysis of the light spectrum – is one of the most powerful tools astronomers use to work out what’s going on, and what it’s like, way out there where the light from the sky originates. Do you know why? If not, then these two NASA webpages will help! Visible Light Waves , and Electromagnetic Spectrum.

It’s such a broad topic, light spectrum, no wonder Universe Today has so many articles on it! For example, Amateur Spectroscopy, Atmosphere of an Extrasolar Planet Measured, and Oops, the Universe is Beige.

Astronomy Cast has several good episodes on the spectrum of light; here’s two to get you started Energy Levels and Spectra, and Detectors.