A few controversial incidents in recent years challenge the idea that light always travels at a constant speed.
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Learn How to Think Like Einstein
Albert Einstein's famous thought experiments led to groundbreaking ideas.
27 August, 2017
Albert Einstein during a lecture in Vienna in 1921. Photo by F. Schmutzer.
<p class="p1">Albert Einstein is widely considered one of the smartest people who ever lived, significantly impacting our understanding of the world around us. His General Theory of Relativity has redefined what we know about space and time and is one of the pillars of modern physics. What’s also remarkable about Einstein’s achievements is that they relied largely on his mental powers and the intricacy of his imagination. He was able to discern and relate very complex scientific concepts to everyday situations. His thought experiments, that he called <strong><span class="s1"><em>Gedankenexperiments</em> </span></strong><span class="s2">in German, used conceptual and not actual experiments to come up with groundbreaking theories.</span></p> <p class="p3"><span class="s3"><strong>CHASING A BEAM OF LIGHT</strong></span></p> <p class="p3"><span class="s3">One of Einstein’s most famous thought experiments took place in 1895, when he was just 16. The idea came to him when he ran away from a school he hated in Germany and enrolled in an avant-garde Swiss school in the town of Aarau that was rooted in the educational philosophy of <a href="https://en.wikipedia.org/wiki/Johann_Heinrich_Pestalozzi" target="_blank">Johann Heinrich Pestalozzi,</a> which encouraged <strong>visualizing concepts.</strong><span> </span></span></p> <p class="p2"><span class="s3">Einstein called this thought experiment the “</span><span class="s4">germ of the special relativity theory.</span><span class="s3">” What he imagined is this scenario - you are in a vacuum, pursuing a beam of light at the speed of light - basically going as fast as light. In that situation, Einstein thought, that light should appear stationary or frozen, since both you and the light would be going at the same speed. But this was not possible in direct observation or under <strong>Maxwell’s equations,</strong> the fundamental mathematics that described what was known at the time about the workings of electromagnetism and light. The equations said that nothing could stand still in the situation Einstein envisioned and would have to move at the speed of light - <strong>186,000</strong> miles per second.</span></p> <p class="p2"><span class="s3"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODQxMDI3OS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY2MTk3NzQwMH0._9boRUikR90ykMFO8JMqdjzFFH8FmMJUoMHopmMLicA/img.jpg?width=980" id="89391" class="rm-shortcode" data-rm-shortcode-id="2ed7abf087c5332f0941b7134961bde1" data-rm-shortcode-name="rebelmouse-image"><br></span></p> <p class="p3"><em>Artists pose in a laser projection entitled 'Speed of Light' at the Bargehouse on March 30, 2010 in London, England. <span>(Photo by Peter Macdiarmid/Getty Images)</span></em></p> <p class="p3"><span class="s3">Here’s how Einstein expanded on this in his <a href="https://www.amazon.com/Autobiographical-Notes-Albert-Einstein/dp/0812691792" target="_blank">Autobiographical Notes</a>:</span></p> <blockquote>
<p class="p4"><span class="s5">“If I pursue a beam of light</span><span class="s3"> with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as an electromagnetic field at rest though spatially oscillating. There seems to be no such thing, however, neither on the basis of experience nor according to Maxwell's equations. From the very beginning it appeared to me intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest. For how should the first observer know or be able to determine, that he is in a state of fast uniform motion? One sees in this paradox the germ of the special relativity theory is already contained."</span></p>
</blockquote> <p class="p6"><span class="s3">The tension between what he conceived of in his mind and the equations bothered Einstein for close to a decade and led to further advancements in his thinking.</span></p> <p class="p3"><span class="s3"><strong>LIGHTNING STRIKING A MOVING TRAIN</strong></span></p> <p class="p3"><span class="s3">A 1905 thought experiment laid another cornerstone in Einstein’s special theory of relativity. What if you were standing on a train, he thought, and your friend was at the same time standing outside the train on an embankment, just watching it go by. If at that moment, lightning struck both ends of the train, it would look to your friend that it struck both of them at the same time.</span></p> <p class="p2"><span class="s3">But as you are standing on the train, the lighting that the train is moving towards would be closer to you. So you would see that one first. It is, in other words, possible for one observer to see two events happening at once and for another to see them happening at different times.</span> </p> <blockquote>
<p class="p7"><span class="s3">“Events that are simultaneous with reference to the embankment are not simultaneous with respect to the train,” <a href="https://www.nytimes.com/2015/11/01/opinion/sunday/the-light-beam-rider.html?mcubz=0&_r=0" target="_blank"><span class="s6">wrote</span></a> Einstein. </span></p>
</blockquote> <p class="p3"><span class="s3">The contradiction between how time moves differently for people in relative motion, contributed to Einstein’s realization that time and space are relative.</span> </p> <p class="p3"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODQxMDI4MC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNTAwMzI5Mn0.egBSxUFSiEziOgrJCv_10LH4a1RXoMOVMqU_4opxhMI/img.jpg?width=980" id="f604d" class="rm-shortcode" data-rm-shortcode-id="dff63af1cf75acd88c96d56f24597103" data-rm-shortcode-name="rebelmouse-image"></p> <p class="p3"><em>Lightning strikes during a thunderstorm on July 6, 2015 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)</em></p> <p class="p3"><span class="s3"><strong>MAN IN FALLING ELEVATOR</strong></span></p> <p class="p3"><span class="s3">Another thought experiment led to the development of Einstein’s General Theory of Relativity by showing that gravity can affect time and space. Here’s how he described it happened:</span></p> <blockquote>
<p class="p7"><span class="s3">“I was sitting in a chair in the patent office at Bern when all of a sudden a thought occurred to me,” <a href="https://www.nytimes.com/2015/11/01/opinion/sunday/the-light-beam-rider.html?mcubz=0&_r=0" target="_blank"><span class="s6">he remembered.</span></a> “If a person falls freely, he will not feel his own weight.” He later called it “the happiest thought in my life.”</span></p>
</blockquote> <p class="p2">A 1907 thought experiment expanded on this idea. If a person was inside an elevator-like “chamber” with no windows, it would not be possible for that person to know whether he or she was falling or pulled upward at an accelerated rate. Gravity and acceleration would produce similar effects and must have the same cause, proposed Einstein. </p> <blockquote>
<p class="p7"><span class="s3">“The effects we ascribe to gravity and the effects we ascribe to acceleration are both produced by one and the same structure,”<span> </span></span><span class="s3"><a href="https://www.nytimes.com/2015/11/01/opinion/sunday/the-light-beam-rider.html?mcubz=0&_r=0" target="_blank">wrote Einstein.</a></span></p>
</blockquote> <p class="p9"><span class="s3">One consequence of this idea is that gravity should be able to bend a beam of light - a theory confirmed by a 1919 observation by the British astronomer Arthur Eddington. He measured how a star’s light was bend by the sun’s gravitational field.</span></p> <p class="p3"><span class="s3"><strong>THE CLOCK PARADOX AND THE TWIN PARADOX</strong></span></p> <p class="p3"><span class="s3">In 1905, Einstein thought - what if you had two clocks that were brought together and synchronized. Then one of them was moved away and later brought back. The traveling clock would now lag behind the clock that went nowhere, exhibiting evidence of <a href="https://en.wikipedia.org/wiki/Time_dilation" target="_blank"><strong>time dilation</strong></a><strong> </strong>- a key concept of the theory of relativity.</span></p> <blockquote>
<p class="p10"><span class="s8">“</span><span class="s3">If at the points A and B of K there are clocks at rest which, considered from the system at rest, are running synchronously, and if the clock at A is moved with the velocity v along the line connecting B, then upon arrival of this clock at B the two clocks no longer synchronize but the clock that moved from A to B lags behind the other which has remained at B,“ wrote Einstein. </span></p>
</blockquote> <p class="p10"><span class="s3">This idea was expanded upon to human observers in 1911 in a follow-up thought experiment by the French physicist <strong>Paul Langevin.</strong> He imagined two twin brothers - one traveling to space while his twin stays on Earth. Upon return, the spacefaring brother finds that the one who stayed behind actually aged quite a bit more than he did.</span></p> <p class="p10"><span class="s3">Einstein solved the clocks paradox by considering <strong>acceleration and deceleration effects and the impact of gravity</strong> as causes of the for the loss of synchronicity in the clocks. The same explanation stands for the differences in the aging of the twins.</span> </p> <p class="p10"><span class="s3">Time dilation has been abundantly demonstrated in atomic clocks, when one of them was sent on a space trip or by comparing clocks on the space shuttle that ran slower than reference clocks on Earth.</span></p> <p class="p3"><span class="s3">How can you utilize Einstein’s approach to thinking in your own life? For one - allow yourself time for introspection and meditation. It's equally important to be open to insight wherever or whenever it might come. Many of Einstein's key ideas occurred to him while he was working in a boring job at the patent office. </span>The elegance and the scientific impact of the scenarios he proposed also show the importance of imagination not just in creative pursuits but in endeavors requiring the utmost rationality. By precisely yet inventively formulating the questions within the situations he conjured up, the man who once said “imagination is more important than knowledge” laid the groundwork for the emergence of brilliant solutions, even if it would come as a result of confronting paradoxes.</p>
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Scientists Weigh a White Dwarf Star, Prove Einstein Right
Astronomers make the first direct observation of a phenomenon predicted by Albert Einstein's theory of general relativity.
11 June, 2017
White Dwarfs. Image credit: NASA and H. Richer (University of British Columbia)
<p class="p1"><span class="s1">Albert Einstein’s theory of general relativity predicted that the gravity of stars could brighten and bend the light coming from other stars like a magnifying lens. Yet this is something Einstein did not think we could ever see due to the great distance between stars, writing in a 1936 article that </span><span class="s2">"there is no hope of observing this phenomenon directly."</span></p> <p class="p1"><span class="s1">Yet, as science persists, this phenomenon, called <strong>“gravitational microlensing”,</strong> has <a href="http://science.sciencemag.org/content/early/2017/06/06/science.aal2879" target="_blank">now been observed</a> by an international team of researchers, led by <strong>Kailash C. Sahu</strong>, </span><span class="s2">an astronomer at the Space Telescope Science Institute in Baltimore, Maryland.</span> </p> <p class="p3"><span class="s3">Writing in <a href="http://science.sciencemag.org/content/356/6342/1015" target="_blank"><span class="s1">an accompanying paper</span></a>, <strong>Terry D. Oswalt</strong> from the </span><span class="s1">Embry-Riddle Aeronautical University, says that Einstein would be proud of this accomplishment because “one of his key predictions has passed a very rigorous observational test."</span></p> <p class="p3"><span class="s1">Gravitational microlensing was initially observed in 1919 by measuring starlight that curbed around the total eclipse of the Sun. This is the first time, however, that the effect was seen involving stars other than our sun.</span> </p> <p class="p3"><span class="s1">When a star passes between us and a background star, a circular ring of light forms called the <strong>“Einstein ring”.</strong> What Sahu’s team observed by using data from the <a href="http://hubblesite.org/" target="_blank">Hubble Space Telescope</a> was an asymmetrical version of an Einstein ring, with the distant star appearing to be off-center from its actual position due to the bending of the light - a process called <strong>'astrometric lensing’.</strong></span></p> <p class="p3"><span class="s1"><strong> </strong>The researchers found this by measuring the shifts in the position of a distant star as its light was being deflected by a nearby <a href="https://imagine.gsfc.nasa.gov/science/objects/dwarfs2.html" target="_blank"><span class="s2">white dwarf</span></a> star.</span></p> <p class="p3"><span class="s1"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODMzOTY5Ny9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzOTg5OTg1MH0.dZuaK6O2j-iJP1hfqCSsQJF-wHppow6QpPG3DIFgJnk/img.jpg?width=980" id="f2a86" class="rm-shortcode" data-rm-shortcode-id="f6ff2b0f531fa00b98dfe986fe320fb2" data-rm-shortcode-name="rebelmouse-image"><br></span></p> <p><!-- p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; line-height: 16.0px; font: 14.0px Arial; -webkit-text-stroke: #000000} span.s1 {font-kerning: none} --> </p><p class="p1"><em><span class="s1">The gravity of a white dwarf star warps space and bends the light of a distant star seen behind it. Credit: NASA, ESA, and A. Feild (STScI)</span></em></p> <p class="p3"><span class="s1">Another achievement from Sahu’s research is giving scientists a tool in <strong>estimating the mass of stars.</strong></span></p> <blockquote><p class="p1"><span class="s1">"The research by Sahu and colleagues provides a new tool for determining the masses of objects we can't easily measure by other means. The team determined the mass of a collapsed stellar remnant called a white dwarf star. Such objects have completed their hydrogen-burning life cycle, and thus are the fossils of all prior generations of stars in our Galaxy, the Milky Way,” <a href="http://science.sciencemag.org/content/356/6342/1015" target="_blank">explains Oswalt</a>, an expert in white dwarfs.</span></p></blockquote> <p class="p1"><span class="s1">Here’s how you would use light to weigh stars, thanks to <a href="http://science.sciencemag.org/" target="_blank">Science</a> magazine:</span></p> <p class="p2"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODMzOTY5OS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxODI0MzAyOH0.qeOH-VgDpENpJGtnb-tKtim9gBl-dZE5UI4ryo3D6sQ/img.jpg?width=980" id="4c589" class="rm-shortcode" data-rm-shortcode-id="365cec065a92546ff0dff0fbb87d63cb" data-rm-shortcode-name="rebelmouse-image"></p> <p class="p1"><span class="s1">And here’s Professor Terry Oswalt explaining the significance of Sahu’s work, showing a hands-on demonstration that you can try at home:</span></p> <p><span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="fd9f8b616334a0df61fb8e054c4465bc"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/SPrCBeL8bKw?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span></p>
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1 Number Will Soon Reveal If the Speed of Light Used to Be Faster
Scientists produce a value for the cosmic microwave background that will definitely prove or disprove that the speed of light used to be higher.
26 November, 2016
Big bang (FILTER FORGE)
<p class="p1">According to Einstein’s theory of relativity, the speed of light in a vacuum and gravity are the same. This is nice and orthogonal, but if the universe began with a hot big bang <a href="https://map.gsfc.nasa.gov/universe/uni_age.html" target="_blank"><span class="s1">13.77 billion years ago</span></a> give or take .059 billion years, there’s a problem scientists have been struggling to explain. If light particles and gravity waves travel at the same speed, there simply hasn’t been enough time for the universe to become as evenly heated as it seems to be. Light — and thus, energy and heat — just doesn’t travel fast enough to have reached across its entire radius in roughly 14 billion years. The prevailing explanation is the “inflation theory” in which the universe at first expanded slowly enough for it to reach a uniform temperature, and then picked up speed to reach its current estimated radius of <a href="http://phys.org/news/2015-10-big-universe.html" target="_blank"><span class="s1">46 billion light years across</span></a>. However, many feel that inflation is an idea lacking in evidence or a logical mechanism. Another idea is that <a href="http://curious.astro.cornell.edu/about-us/101-the-universe/cosmology-and-the-big-bang/general-questions/571-did-the-speed-of-light-change-over-the-history-of-the-universe-intermediate" target="_blank"><span class="s1">the speed of light used to be faster</span></a>, and now a team of scientists have come up with something unique in this field: A way to definitively test a theory.</p> <p class="p1">The issue the ideas are attempting to address is called the “horizon problem.” If you could see to the farthest star (we <a href="https://youtu.be/bd0vuQ8ml4E" target="_blank"><span class="s1">can’t actually see nearly that far</span></a> with the naked eye) on your left, it would be 14 billion light years away, or 14 billion years in the past. At your far right would be another 14-billion-year-old star. Scientists would say that both stars are in “causal contact” with us because their light has reached us, and causal contact is something that’s required for energy/heat to be exchanged.</p> <p class="p1"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODQwOTAxMi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNzY4ODc2MH0.Vso5fmuueeq0YR15qlW-smyHp5ZH1NTn8mjDewHP5qU/img.jpg?width=980" id="0d4b2" class="rm-shortcode" data-rm-shortcode-id="193987291a5a6de20081e320bcd0de05" data-rm-shortcode-name="rebelmouse-image"></p> <p class="p2"><span style="color: #737d83; font-size: 13px;">Night sky (</span><a href="https://secure.flickr.com/photos/ryanhallock/" style="font-size: 13px;"><span class="s3">RYAN HALLOCK</span></a><span style="color: #737d83; font-size: 13px;">)</span></p> <p class="p2">On the other hand, the distance between our far left and far right stars would be 28 billion light years, and that means two people standing on those stars wouldn’t be able to see each other yet because it would take 28 billion years for light to travel between them and the universe is only 14 billion years old. These stars are not in causal contact, and thus no energy/heat has yet had time to travel between them. So why does the spectral index, a reading of the cosmic microwave background (CMB) — a snapshot of the oldest light in the universe — show the same temperature everywhere?</p> <p class="p1"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODQwOTAxMy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxMzE2ODM0M30.bhT032BxitGcf6k6_g9WT6Pttg6HJhTQZCMcolb8C5U/img.jpg?width=980" id="86e11" class="rm-shortcode" data-rm-shortcode-id="0325d7aa492b0234cdd2c02931bb3886" data-rm-shortcode-name="rebelmouse-image"></p> <div class="image-caption">CMB image from 2010 (<a href="http://map.gsfc.nasa.gov/media/121238/ilc_9yr_moll4096.png"><span class="s1">NASA/WMAP</span></a>)</div> <div class="image-caption"></div> <p class="p1">One of the people who first put forward the idea that the speed of light might have been faster at some point and thus able to overtake the outward expansion of matter was <a href="http://www.imperial.ac.uk/people/j.magueijo" target="_blank"><span class="s1">João Magueijo</span></a> from Imperial College London. He’s now developed, along with <a href="https://www.perimeterinstitute.ca/people/niayesh-afshordi" target="_blank"><span class="s1">Niayesh Afshordi</span></a> at the Perimeter Institute in Canada, a <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.101301" target="_blank"><span class="s1">model that predicts a very specific spectral index value</span></a> that would confirm the speed of light used to be higher: 0.96478. Current readings of the CMB are not that far off — 0.968 — and they’re getting more precise all the time. It’s Magueijo’s hope that in the near future, the <a href="http://www.skyandtelescope.com/astronomy-news/planck-upholds-standard-cosmology-0210201523/" target="_blank"><span class="s1">Planck satellite measuring the CMB</span></a> will either match the model’s prediction, proving the theory, or definitively contradict it, thus ruling it out.</p> <p class="p1"><img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xODQwOTAxNC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYxMzM4OTY1Nn0.gJEk5k8tOS8Uy_QlwalJKW9ih8bRUJrsYmr8XTYYygg/img.jpg?width=980" id="0c2c7" class="rm-shortcode" data-rm-shortcode-id="eab398eb0409a4aba16c7a8bc34edd9b" data-rm-shortcode-name="rebelmouse-image"></p> <div class="image-caption">Planck satellite (<a href="http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA16881"><span class="s1">JPL/NASA</span></a>)</div> <div class="image-caption"></div> <p class="p1">Magueijo tells <a href="https://www.newscientist.com/article/2113797-gravity-may-have-chased-light-in-the-early-universe/" target="_blank"><span class="s1"><em>New Scientist</em></span></a>, “That would be great — I won’t have to think about these theories again. This whole class of theories in which the speed of light varies with respect to the speed of gravity will be ruled out."</p> <p class="p1">You might expect Magueijo to be pulling for his theory to be confirmed, but really, he’s just hoping for one irrefutable answer in a field that’s made up almost entirely of so-far unprovable theories. Which is to say, he’s just looking for some plain-old truth.</p>
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