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Caution: Mind-bending concepts ahead... Perhaps you’ve heard of light sails (or solar sails). These are huge parachute-like sails that can be expanded in space to allow the pressure from light emitted from the sun to propel a spacecraft. The first spacecraft to demonstrate that this actually works was the Japanese craft IKAROS in 2010. Think about how odd this seems—light emitted by the sun can actually push something. This must mean that light must weigh something, right? Well, first it’s important to understand the difference between weight and mass. MASS is the total amount of matter, or stuff, an object contains. WEIGHT is the force of gravity on an object. I typically weigh 190 pounds (86 kg). On Earth, my weight and my mass are the same—190 pounds. But, if I go to the moon, where there is less gravity, my weight and mass are no longer the same. My mass is still 190 pounds, but my weight is only 32 pounds. On Mars, my mass is still 190 pounds, but I weigh 72 pounds. Remember, mass is how much stuff there is in an object, so mass does not change in situations with different gravity. Weight does change. Light is made up of photons, and photons do not have mass. So, a simple answer to this question is NO… light does not have mass, and therefore it does not have weight. But things aren’t that simple. Light actually has momentum (if you’re wondering how something without mass can have momentum, that’s beyond my ability to explain… it has to do with the fact that light also has energy… light is kind of weird). Anyway, light does indeed have momentum, and it can exert pressure on a surface. This is why light sails work. This is why, when I stand in direct sunlight, I weigh slightly more than when I stand in the shade. The sunlight from above pushes me downward with a slight amount of force. On a sunny day, the city of Chicago weighs 140 kilograms more than at night, simply because sunlight is pushing down on it. Here’s a tidbit that blows my mind: If you captured all the sunlight falling on Chicago in any moment and put that sunlight in a box that has perfect mirrors on the inner walls—mirrors that reflect 100% of the light so that the photons are continually reflected back and forth in the box, the box would then weigh 140 kg more than it did before. And in space, where the box has mass but no weight, more force would be required to accelerate the box. So, this seems like light has mass, right? Not exactly. Because it is the energy and momentum of the light that causes this to happen. Instead of saying the light in the box has mass, it is more accurate to say the light in the box contributes to the total mass of the box. What a weird and wonderful universe we live in! (this is a conceptual image of a spaceship with a solar sail)  Photo Credits: - Ship with solar sail - Midjourney v. 6.1
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Trish and I recently spent a week at the Author Nation conference in Las Vegas. We were so busy learning and being inspired by other authors that we hardly even had time to leave the hotel. However, our room had a great view of the skyline, including the amazing new structure called The Sphere. This beautiful but rather gaudy structure is a wonder of technological achievement, so I thought you might want to know some interesting facts about it. First, The Sphere is the largest spherical building in the world, at 366 feet (111 m) tall and 516 feet (157 m) wide. For reference, the Statue of Liberty (including the statue and the pedestal) is 306 feet tall and could easily fit inside The Sphere. To position the pieces, they used the fourth largest crane in the world, which had to be brought from Belgium for this job. The exterior shell is actually an elaborate spherical video screen, consisting of 1.2 million programmable LEDs. That's 580,000 square feet (53,880 square m) of screen. The videos are clearly visible even in daylight. And, from what we could tell, the videos run 24 hours a day. Of course, Vegas is illuminated by countless other gaudy light displays, so what's another 1.2 million more? Although I haven't seen the inside, it's supposedly just as impressive, if not even more so. The inside is a concert stadium with 18,600 seats, and with standing room for another 20,000 people. Get this... 10,000 of those seats are extra special. They provide an immersive experience, with specialized sound systems, haptic seats that make the guests “feel” sound vibrations, and machines that create wind, temperature, and even scent effects. I'm not even kidding. Yes, there's a concert stage, but the interior screen is the highest resolution screen in the world (268 million video pixels with 16K resolution). Supposedly, this makes it ten times clearer than the best HD TVs on the market today. To make sure the concerts are loud enough, there are 1,586 loudspeakers. So, you might be thinking... Cool, I want to experience it! Or maybe... Yuck, that's too much light and sound! At least now you know more about it.   Seriously, who made this town in England the boss of time? And why? Let’s start with some history. Throughout most of human history, the best way humans could keep track of time was to look up at the sun and make an estimate based on its position. Eventually, clocks were invented, dramatically improving punctuality. By the 1800s, clocks and pocket watches were accurate to within less than a second. The problem was, people in different places set their clocks differently, usually based on when the sun would set or rise. The result? Times were different in different places, and when people traveled, they would have to reset their watches whenever they arrived at a destination, to match the local time. This got to be a serious problem in the 1800s when railroads became a popular way to travel. Imagine trying to run a complex schedule of arrival and departure times when each location had clocks that were slightly out of synch with other locations. A lot of people missed their trains because their own clocks were different from the railways’ clocks. In the 1850s, countries in Europe decided to establish a standard time, such as London time for all of England, and Rouen time for France. However, the USA was so large that, on November 18, 1883, the US adopted four time zones, which were meticulously established by a group of railroad operators. Each time zone had a standard time that everyone could set their clocks to. Well, that’s fine and dandy, but it did not meet the need for a standard global time. So, in 1884, the US held the International Meridian Conference in Washington D.C. Experts from dozens of countries attended, and the group selected the global prime meridian (a prime meridian is an arbitrarily chosen line of longitude defined as zero degrees) as the starting point to measure all time zones. This line of longitude passes through Greenwich, England, so it’s also called the Greenwich Meridian. Why choose the Greenwich Meridian to start all time zones? Because, for centuries, Greenwich was home of the Royal Observatory. The clock there was already being used to set the official London time. At that time, the British Empire had a huge impact on international shipping, and the British had created countless sea charts and schedules based on Greenwich Mean Time that were already used by mariners from many countries. So, it seemed a natural choice for the entire world to set all clocks based on Greenwich Mean Time. Then, of course, people had to go and mess everything up with pesky daylight savings time nonsense.  |
Stan's Cogitations
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January 2025
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