understanding colors

In this video Neil deGrasse Tyson explains the Physics behind colors.

You can check this lesson, and create a copy from here (if you like it).

Here is another lesson as well (about light pollution):

ODS Summer School - Project Scenario by José Gonçalves de eufisica

Another educational scenario

International Dark Sky Week

Light Pollution Wastes Energy (Infographic)

International Dark Sky Week (April, 4 to 10) draws attention to the widespread environmental impacts of light pollution and promotes simple solutions to solve it. Learn more about International Dark Sky Week.

In order to help you spread the word about light pollution, the International Dark-Sky Association put together some resources for you. Check back regularly this link for new stuff.

Red Filter Glasses

Enjoying this summer...
Now I made another tool to teach light and color in my Physics class.
Take a look:

Gravitational potential and speed of light

Remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave. Credit: ALMA/NASA

(Phys.org) —Physicist James Franson of the University of Maryland has captured the attention of the physics community by posting an article to the peer-reviewed New Journal of Physics in which he claims to have found evidence that suggests the speed of light as described by the theory of general relativity, is actually slower than has been thought.

Read more at: http://phys.org/news/2014-06-physicist-slower-thought.html#jCp

The paper is available in IOP website.

Refraction of Light

Here is some photos taken at class to teach light's refraction.

To learn more about this topic try to find refraction in the search option.
You can also play with this PhET simulation:

Click to Run

Mini-Spectrometer... how to build

In this post you can find the links to create this foldable mini-spectrometer.
Here is the video with the steps to create one:

And here is my first picture that I took with my smartphone:

Mini-Spectrometer

In a earlier post, I published how to build a spectrometer with house stuff. Now, a Physics teacher (friend of mine) show me this great website that show us how to build a mini-spectrometer. You can attach to an smartphone, laptop, or computer with a camera and submit your image to http://spectralworkbench.org/ (point your browser to the website and click "capture").

Light waves, visible and invisible - Lucianne Walkowicz

IBSE about Light Pollution

Here is my presentation that happened in the Discover the Cosmos Conference (Volos, Greece - 2013).

The presentation was an Inquiry Based Science Education (IBSE) scenario about Light Polution:

Light pollution from eufisica

You can download the worksheets here: http://portal.discoverthecosmos.eu/en/node/195700

STOP that light

Credit: Adrian

The fastest thing in the universe was completely stopped and stored for a minute (new record). In vacuum, light travels about 18 million kilometers, in those 60 seconds - which represents more than 20 trips to the moon and back.

"A minute is a very, very long," says Thomas Krauss, St. Andrews University, UK. "This is really an important milestone."

The exploit could allow secure quantum communications to work at long distances.

As the light typically travels just under 300,000 kilometers per second in a vacuum, physicists  were able to slow it down just to only 17 meters per second in 1999, and two years later, stop it completely, though only by a fraction of a second. Earlier this year, researchers increased this time stopping the light for 16 seconds using cold atoms.

Light Trap

To break the minute barrier, George Heinze and colleagues at the University of Darmstadt, Germany, fired a laser control over an opaque crystal, the atoms leading to a quantum superposition of two states. This made it clear to a small range of frequencies. The Heinze's team then stopped a second laser beam which entered the crystal, turning the first laser off and, consequently, the transparency of that crystal disappeared.

The storage time depends upon the crystal's superposition. A magnetic field extends it, but it complicates the configuration of the control laser. Heinze's team used an algorithm to "generate" the magnets and laser combinations, leading them to trap the light for a minute.

Should still be possible to achieve longer storage of light with other crystals, Heinze says, as they did with the physical limits of this material.

Fonte: newscientist

Journal reference: Physical Review Letters, doi.org/m86

Light pulses in a quantum walk

The principle of quantum random motion in two dimensions: At a node, a light pulse can continue on its journey through a network of optical fibres in four directions: forwards, backwards, to the right or to the left. As a quantum object, it is in fact at all the locations that are on the possible routes to a destination. Credit: MPI for the Science of Light/University of Paderborn 

Tourists who drift aimlessly during a sightseeing tour are moving randomly - just like electrons that move from one atom to the next. To obtain a better understanding of these random motions it is often useful to reduce their complexity. Physicists do this by simulating random walks. These simulations can bring new insights in the quantum world as well. Researchers at the Max Planck Institute for the Science of Light and the University of Paderborn and their colleagues are now the first to successfully realize an arrangement for a quantum walk in two dimensions. The experimental setup can be used to investigate many quantum phenomena.

in PhysOrg

Multidimensional quantum walks can exhibit highly nontrivial topological structure, providing a powerful tool for simulating quantum information and transport systems. We present a flexible implementation of a two-dimensional (2D) optical quantum walk on a lattice, demonstrating a scalable quantum walk on a nontrivial graph structure. We realized a coherent quantum walk over 12 steps and 169 positions using an optical fiber network. With our broad spectrum of quantum coins, we were able to simulate the creation of entanglement in bipartite systems with conditioned interactions. Introducing dynamic control allowed for the investigation of effects such as strong nonlinearities or two-particle scattering. Our results illustrate the potential of quantum walks as a route for simulating and understanding complex quantum systems.

in ScienceMag

 

Neutrino's Saga - final chapter?

Time of flight difference between the speed of light and the arriving neutrinos. Observe a great difference between the two experiments. Now, we have to wait for the new results of the OPERA experiment, after the cable's problem.

The ICARUS experiment uploaded a paper to the arXiv website with a preprint paper about the neutrinos' velocity, in October 2011, defying the superluminal neutrinos. Now, after the assumption of a problem in a cable, by the OPERA team, ICARUS published a preprint paper that confirms the previous results that neutrinos doesn't travel with a speed superior that the speed of light. 

So, we have to wait for the OPERA results (we need a large number of events and it takes... days), to confirm that neutrinos aren't superluminal.

Here is the abstract:

Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam

The CERN-SPS accelerator has been briefly operated in a new, lower intensity neutrino mode with ~10^12 p.o.t. /pulse and with a beam structure made of four LHC-like extractions, each with a narrow width of ~3 ns, separated by 524 ns. This very tightly bunched beam structure represents a substantial progress with respect to the ordinary operation of the CNGS beam, since it allows a very accurate time-of-flight measurement of neutrinos from CERN to LNGS on an event-to-event basis. The ICARUS T600 detector has collected 7 beam-associated events, consistent with the CNGS delivered neutrino flux of 2.2 10^16 p.o.t. and in agreement with the well known characteristics of neutrino events in the LAr-TPC. The time of flight difference between the speed of light and the arriving neutrino LAr-TPC events has been analysed. The result is compatible with the simultaneous arrival of all events with equal speed, the one of light. This is in a striking difference with the reported result of OPERA [1] that claimed that high energy neutrinos from CERN should arrive at LNGS about 60 ns earlier than expected from luminal speed. 

 Read more in DiscoverMagazine.com, CNet and Wired. 

Measure the Speed of Light with Chocolate

"'C' is for chocolate! 'c' is also the symbol used for the speed of light. Defined as being 299,792,458 meters per second in vacuum, you can take a crack at measuring the ultimate speed using your microwave, a ruler and a bar of chocolate! Yum!" (Jefferson Lab - YouTube)

Well, lets see how they do it:

And now the calculations:

To calculate the speed of light, we can use the math's expression of speed:

v = Dx/Dt

In this case, Dx = l and Dt = T and T = 1/f (T is the period and f the frequency of the wave, and l the wavelength).
The holes that appear in the chocolate corresponds to the maximum and minimum in a steady wave. So the wavelength is two times this distance:
l = 2 x 7.1 cm = 2 x 7.1 x 10^-2 m
The frequency can be read in the back of your microwave. In this case, the value corresponds to f = 2 450 MHz = 2 450 x 10⁶ s^-1.


So, velocity is:
v = l x f <=> v= 2x(7.1 x 10^-2 m) x (2 450 x 10⁶ s^-1) = 3.48 x  10⁸ m s^-1 .


That brings a percent error:


e = |c - v|/|c| x 100 = | 2.99 x  10⁸ - 3.48 x  10⁸|/|2.99 x  10⁸| x 100 = 16 %

Electromagnetic momentum density in matter solved

Optical Force Measurement. Credit: eecs.northwestern.edu

"(PhysOrg.com) -- Researchers from the NIST Center for Nanoscale Science and Technology and the University of British Columbia have shown that the interaction between a light pulse and a light-absorbing object, including the momentum transfer and resulting movement of the object, can be calculated for any positive index of refraction using a few, well-established physical principles combined with a new model for mass transfer from light to matter."

Electromagnetic radiation, like light, carries momentum and can transfer its momentum to matter via radiation pressure. In the past century, there has been a controversy over the correct form of the electromagnetic momentum density in matter.

There was two forms:

•  In the “Minkowski formulation,” the momentum density is proportional to the index of refraction;
• in direct contrast, the “Abraham formulation” finds it to be inversely proportional. 

And the two equations for the momentum in a dielectric with refractive index n are:

• The Minkowski version:

• The Abraham version:

where h is the Planck constant, ν is the frequency of the light and c is the speed of light in vacuum.

In 2011, an optical experiment was performed to study this problem based on first principles. It tested the velocity-addition formula of light in a reversed Fizeau experiment. The result was that the light speed c= 299,792,458m/s in vacuum of Lorentz transformation should be replaced by c/n to describe electrodynamic phenomena in a dielectric medium^[1] Consequently, the momentum of a photon in vacuum is p=E/c and the value should be p=E/(c/n)=nE/c in media, although it is not measured directly.^[2] It is asserted, that this confirms Minkowski's formulation.

[1] Wang Zhong-Yue, Wang Pin-Yu, Xu Yan-Rong (2011). "Crucial experiment to resolve Abraham-Minkowski Controversy". Optik 122 (22): 1994–1996. doi:10.1016/j.ijleo.2010.12.018

[2] Wang, Zhong-Yue. Graphene, neutrino mass and oscillation. arXiv:/0909.1856

The recently published in Applied Physics support the Abraham formulation: Revisiting the Balazs thought experiment in the presence of loss: electromagnetic-pulse-induced displacement of a positive-index slab having arbitrary complex permittivity and permeability, K. J. Chau and H. J. Lezec, Applied Physics A 105, 267-281 (2011).

"The researchers propose a set of postulates for light-matter interaction that encompass: a) the Maxwell equations, which govern classical electromagnetic behavior; b) a generalized Lorentz force law, which describes the force felt by matter in the presence of an electromagnetic field; c) a model for electromagnetic mass density transfer to an absorbing medium; and d) the Abraham formulation of momentum density. Using both closed-form calculations and numerical simulations of the interaction between an electromagnetic pulse and a test slab, the researchers demonstrated that their postulates yield results that are consistent with conservation of energy, mass, momentum, and center-of-mass velocity at all times." ( PhysOrg)

Read entire article in PhysOrg

Breaking the speed of light?

Let's break the speed of light in your backyard :)

Let there be light

In the Chalmers scientists’ experiments, virtual photons bounce off a “mirror” that vibrates at a speed that is almost as high as the speed of light. The round mirror in the picture is a symbol, and under that is the quantum electronic component (referred to as a SQUID), which acts as a mirror. This makes real photons appear (in pairs) in vacuum. Credit: Philip Krantz, Chalmers

(PhysOrg.com) -- Scientists at Chalmers University of Technology have succeeded in creating light from vacuum – observing an effect first predicted over 40 years ago. The results will be published tomorrow (Wednesday) in the journal Nature. In an innovative experiment, the scientists have managed to capture some of the photons that are constantly appearing and disappearing in the vacuum.


Complete article here.

The Neutrino's saga - turnaround

The results obtained by ICARUS' team says that neutrinos cannot have the speed equal to the speed of light. Indeed, it's smaller than that in three orders of magnitude.

"The saga of the superluminal neutrinos took a dramatic turn today, with the publication of a very simple yet definitive study by ICARUS, another neutrino experiment at the Gran Sasso Laboratories, who has looked at the neutrinos shot from CERN since 2010."

and

"They find that the energy spectrum of the detected neutrino interactions in ICARUS shows a very nice agreement with the expectation for well-behaved light-speed-moving neutrinos. A very dramatic distortion of that spectrum would instead be expected for the speed measured by OPERA, such that indeed ICARUS can place a very tight constraint on the superluminal speed of the CERN neutrinos: consistent with the speed of light, and not larger than that by more than four part in ten billionths. An order of magnitude looser than the limit obtained with the neutrinos from SN1987a, but still quite tight -and certainly excluding without argument the value of 50 millionths measured by OPERA."

Complete article in science20.com
Article (pré-print): arXiv.org

The Neutrino's Saga - Part 5

It seems interesting how the scientific community try to explain the results of the OPERA experiment. See here, here, and here.






Here are the last results:

• Special relativity and clock synchronization; 

"But were the clocks perfectly synchronized?
Keeping time is again the domain of the GPS satellites which each broadcasting a highly accurate time signal from orbit some 20,000km overhead. But is it possible the team overlooked the amount of time it took for the satellite signals to return to Earth? In his statement, van Elburg says there is one effect that the OPERA team seems to have overlooked: the relativistic motion of the GPS clocks.
Sure, radio waves travel at the speed of light, so what difference does the satellite position make? The truth is, it doesn’t.. but the time of flight does. Here we have a scenario where one clock is on the ground while the other is orbiting. If they are moving relative to one another, this calculation needs to be included in the findings. The orbiting probes are positioned from West to East in a plane inclined at 55 degrees to the equator… almost directly in line with the neutrino flight path. This means the clock on the GPS is seeing the neutrino source and detector as changing."

• Times Of Flight Between A Source And A Detector Observed From A GPS Satellite;

"But there is an additional subtlety. Although the speed of light is does not depend on the the frame of reference, the time of flight does. In this case, there are two frames of reference: the experiment on the ground and the clocks in orbit. If these are moving relative to each other, then this needs to be factored in."

paper: http://arxiv.org/abs/1110.2685

• Cautionary Tale From Neutrinoland (thinking about all the explanations and Physics behind in two published articles)
• No So Fast, Neutrinos (MIT)

"Hughes and Wilczek both guess that scientists will most likely approach the neutrino announcement with a variety of new experiments and do tests with different baselines.
“I would say there’s a 98 percent chance this is a systematic error,” Hughes said."

• Light speed

The recent news of neutrinos moving faster than light might have got everyone thinking about warp drive and all that, but really there is no need to imagine something that can move faster than 300,000 kilometres a second. Indeed, the whole idea is illogical.

• Time reversal: A simple particle could reveal new physics

(PhysOrg.com) -- A simple atomic nucleus could reveal properties associated with the mysterious phenomenon known as time reversal and lead to an explanation for one of the greatest mysteries of physics: the imbalance of matter and antimatter in the universe.

The Neutrino's Saga - Part 3

The OPERA experiment

Roll over Einstein: Law of physics challenged (Update 3)
One of the very pillars of physics and Einstein's theory of relativity - that nothing can go faster than the speed of light - was rocked Thursday by new findings from one of the world's foremost laboratories.
in PhysOrg.com

"[...] As a spokesperson for the MINOS neutrino experiment told Ars yesterday, there are three potential sources of error in the timing measurements: distance errors, time-of-flight errors, and errors in the timing of neutrino production. The vast majority of both the paper and the lecture were dedicated to discussing how these errors were reduced (the actual detection of the neutrinos was only a small portion of the paper).

[...] There are a lot of potential sources of error they know about—the paper’s table lists a dozen of them. Small errors in each of these could add up to something more significant than their total error. Then there are the classic unknown unknowns.

 in wired.com

More in the news Reuters, PhysicsAbout

Attention at FermiLab: http://beaconnews.suntimes.com/news/7807816-418/physics-turned-on-its-ear-catches-attention-at-fermilab.html

See the video of the presentation in a seminar: http://cdsweb.cern.ch/record/1384486/

Interview with Spokeperson Antonio Ereditato & CNRS researcher Dario Aut...