The goal of this blog is to create a list of super facts. Important facts that are true with very high certainty and yet surprising, misunderstood, or disputed by many. This blog aims to be challenging, educational, and fun, without it being clickbait. I determine veracity using evidence, data from reputable sources and longstanding scientific consensus. Prepare to be challenged (I am). Intentionally seek the truth not confirmation of your belief.
Superfact 120: The amount of wealth owned by the billionaires is roughly double as much as the poorest half of the world’s population. The amount of wealth owned by the 12 richest billionaires is more than the wealth of the poorest 50% of the world’s population. The richest 1% of the global population owns approximately 38% to 45% of the world’s total wealth.
US 100 dollar bills falling through the air Shutterstock Asset id: 2555911235 by Caito
There are at the moment of this writing 3,428 dollar billionaires in the world worth 20.1 trillion dollars together. For comparison the poorest 50% of the world’s population holds between $9 trillion to $12 trillion dollars of wealth (about half). According to this report the amount of wealth owned by the poorest half of the world is less than the amount owned by just the 12 richest billionaires. By the time you read this the numbers have probably changed (likely upwards). You can also read more in Wikipedia.
I am specifying that it is in dollars and not let’s say in the Iranian Rial. With respect to the Iranian Rial, I am also a billionaire, and you are probably too (if you own a phone or computer). One dollar can buy roughly 1,300,000 to 1,600,000 IRR. You just need $700 to be a billionaire in the Iranian Rial.
World’s billionaires. Number and total wealth by year. Trillions of dollars. The graph comes from here. <<Link-6>> Katharina Buchholz. Cropped and edited by User:Timeshifter using freeware IrfanView., Public domain, via Wikimedia Commons.
I should say that initially I was just going to list interesting statistics about the super-rich. However, I found myself surprised by the statistics, and I am sure I am not the only one. Therefore, I picked a couple of facts I decided super facts.
The ten richest billionaires in the World
The numbers below are from Forbes Magazine. To see a list of all billionaires in the world, click here. To see a list with numbers that are updated minute by minute, click here.
Amancio Ortega – 148 billion dollars – source Zara
Wealth share of the richest 1%
The richest 1% of the global population owns approximately 38% to 45% of the world’s total wealth, which is more than what 95% of humanity own according to Oxfam. The richest 1% of the global population is not about billionaires, it may very well include you and me. Our World in Data has collected and analyzed the statistics for each country in the world. The top richest 1% in the United States own 34.78% of the wealth in the United States. The top richest 1% in Russia own 48.99% of the wealth in Russia. The top richest 1% in Sweden own 27.49% of the wealth in Sweden. The top richest 1% in the Netherlands own 13.98% of the wealth in the Netherlands. See the graphs below from Our World in Data.
The share of wealth owned by the richest 1% of the population. Wealth is defined as the total value of non-financial and financial assets (housing, land, deposits, bonds, equities, etc.) held by households, minus their debts. Data source: World Inequality Database (WID.world) (2026) – Learn more about this data OurWorldinData.org/economic-inequality | CC BY
As you can see from the graphs below the extreme inequality is nothing new. Europe was extremely unequal in the 19th century. The 1% owned 58.01% of the wealth in 1900. The United States was relatively equal in 1978 when the 1% owned 21.79% of the wealth. Russia became very unequal since 1995. I suggest that you play around with the graphs yourself .
The historic share of wealth owned by the 1% for different countries around the world, starting in 1820. Data source: World Inequality Database (WID.world) (2026) – Learn more about this data OurWorldinData.org/economic-inequality | CC BY
ABBA’s Money, Money, Money
Note: This post is not an implicit suggestion that we should tax billionaires more or less, and not about how or whether we should solve inequality, and it is not about politics. It is just surprising statistics regarding wealth and the reality of inequality.
Superfact 119: Heat waves are becoming significantly more frequent, intense, and longer-lasting globally due to human-caused climate change. The combination of a high temperature and humidity can create a high so called wet-bulb temperature that you cannot survive unless you can find a way to cool down. High humidity and heat can make it impossible to cool off through sweating, which rapidly leads to heatstroke. It is estimated that this kills about 500,000 people annually.
Imagine that it is a hot and humid day, but you want to go for a hike for a few hours. It is 104 degrees (40 Celsius) and humid, but you don’t know how humid. You are concerned about the Wet-bulb temperature. You use the Wet Bulb calculator and you find out that a relative humidity of 70% will yield a Wet-bulb temperature of 35 Celsius, which is deadly. You won’t survive that. A relative humidity of 45% will yield a Wet-bulb temperature of 30 Celsius, which is very dangerous but survivable for a healthy person.
Large increases in both the frequency and intensity of extreme weather events (for increasing degrees of global warming) are expected. RCraig09, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons.
I should say that the Wet-bulb temperature of 95 Fahrenheit / 35 Celsius is more of an upper limit for survivability, like a suicide temperature. Wet bulb temperatures below 35 Celsius can also be very dangerous, at least for some people. As mentioned, excess heat and humidity kill about 500,000 people annually. You can read more here or here.
I was first made aware of the Wet-bulb temperatures when I read a science fiction novel focused on climate change, a so called Cli-Fi novel, the Ministry for the Future by Kim Stanley Robinson. It was a dystopian novel with the premise that 20 million Indians died because the Wet-bulb temperature became deadly in a large area in India, and not many people had air conditioning. Also, animals including wildlife and cattle died because, well obviously they did not have air-conditioning.
What followed was international crises, revenge and terrorism by the survivors against those whom they believed to be most responsible for our global warming / climate change, and desperate geo-engineering solutions to cool the planet. At first, I thought it seemed exaggerated but then I learned that dozens of places have already reached deadly Wet-bulb temperatures. Hopefully, a catastrophe like that will never happen but it is not entirely implausible.
The existence of the Wet-bulb temperature scale was a surprise to me. I knew that if you got locked into a Sauna for a long time you would not survive. Accidents that like that have happened in Sweden where I grew up. I did not know that the same thing could happen at natural temperatures. It made me realize that the more frequent, intense, and longer-lasting heat waves we are experiencing is a serious issue. I consider this to be a super fact because it is a true and important fact that many are unaware of.
What is the wet bulb temperature?
The wet bulb temperature is the lowest temperature to which a body can cool down through the evaporation of water (like sweating). It is measured using a thermometer covered in a water-soaked cloth. Because evaporation absorbs heat, the wet bulb temperature is lower than the actual air (dry bulb) temperature. When it is dry outside, sweat evaporates rapidly, keeping you comfortable. When it is humid, the air is already saturated, making it difficult for sweat to evaporate.
The humidex index, real feel and the wet-bulb all take both temperature and humidity into account, but Wet-bulb is focused on the body’s ability to cool down and is a safety measure. For example, if the Wet-bulb temperature is 28 Celsius then a body hotter than that (a human body is 37 Celsius) can lower the temperature via evaporation (sweating). So, a Wet-bulb temperature of 28 Celsius is not a problem (in that regard).
However, if the Wet-bulb temperature is 37 then the human body cannot use evaporation to cool down. Sweating won’t do anything. You’ll overheat and die. A Wet-bulb temperature of 35 is close enough to 37 for your evaporation system to fail and you’ll die. Basically, humidex is about feel, and Wet bulb about whether the body’s cooling system will work.
Our emissions seemed to have peaked, what is the worry ?
I have stated in other posts that thanks to the expansion of renewable energy our carbon emissions have taken a different path lately and that it looks like our emissions have started to go down, so what is the worry? It is important to understand that the average temperatures are not directly tied to our emissions but to the total amount of greenhouse gases in the atmosphere, for example, CO2 (an important greenhouse gas) leaves the atmosphere very slowly, and any level of excess CO2 emissions will keep accumulating.
Before we humans came along there was a balance, the soil, volcanoes, etc., added CO2 and roughly the same amount left the atmosphere. The so called carbon cycle. Imagine a bathtub with a drain that is slowly emptying water and a faucet adding about the same amount. Then we came along and sped up the faucet. For example, humans add roughly 60 to 100 times more CO2 to the atmosphere each year than all the volcanoes on the planet combined. Note: Our current administration is trying to censor climate science related information from NOAA and NASA, so tell me if the link in the previous sentence has stopped working.
The faucet is adding water to the bathtub faster than the drain is emptying the water, so it keeps filling up. The same is true for the CO2 in our atmosphere. Our emissions correspond to the faucet. I generated this picture with the help of ChatGPT.The faucet is adding water to the bathtub a little bit slower than in the previous picture but still faster than the drain is emptying the water, so the bathtub still keeps filling up, but a little bit slower. That is why the problem with heat waves will keep getting worse despite us doing a little bit better with our emissions. I generated this picture with the help of ChatGPT.
Superfact 118: There are more than 100 million forcibly displaced people in the world, including more than 30-40 million refugees, 9 million asylum seekers, and more than 70 million internally displaced persons. The number of refugees in the world has almost tripled since the year 2000 and the number of internally displaced persons is estimated to have more than ten doubled since the year 2000.
Drone footage of thousands of Afghan refugees returning from Pakistan, Pakistan border, refugee camp, Torkham Border. Nangarhar, Afghanistan 8 November 2023. Shutterstock asset id: 2385658471 by Waheedullah Jahesh.
According to Wikipedia the number of refugees is 41.6 million worldwide, 72.1 million internally displaced persons, 8 million asylum seekers and 122.6 million forcibly displaced people in total globally. The number of refugees in the year 2000 was 12,129,600 and the number of internally displaced persons in the year 2000 was 5,998,500.
According to the refugee council of Australia there were 117.8 million forcibly displaced persons in 2025 including 34.4 million refugees, 9 million asylum seekers, and 73.5 million internally displaced persons. According to Our World in Data a record 83 million people globally were living in internal displacement at the end of 2024.
Internally displaced children from other parts of Ukraine in the Zakarpattia Oblast of western Ukraine. UNICEF Ukraine from Kyiv, Ukraine, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons.
I should explain that a refugee is someone who has been forced to flee their home country to escape war, violence, or persecution. A refugee who acquires a new citizenship or returns to his country stops being a refugee. An internally displaced person is an individual who was forced to leave their home or place of residence but did not cross an international border.
It should be noted that World War II was the largest forced displacement event in recorded human history. 65 million people were forcibly displaced in Europe alone according to the Imperial War Museum. The partition of India and Pakistan in 1947 resulted in 12-20 million people being forcibly displaced according to this article. The Afghanistan war resulted in around 10 million people being forcibly displaced according to this article. Today most refugees (65%) come from just five countries Syria, Venezuela, Ukraine, Afghanistan, and Sudan.
Having tens of millions of refugees and forcibly displaced persons is nothing new. What may come as a surprise to many is first of all the size of the numbers and the fact that despite the reduction of causalities from wars in the 21st century compared to previous centuries; the refugee and forcibly displaced persons problem has grown significantly larger over the last couple of decades. Since this is an important but surprising reality, I consider it a super fact.
Where Are the Internally Displaced Persons ?
Internally displaced people, 2024. Internally displaced people had to leave their homes because of violence or disaster and have not crossed an international state border. This counts all individuals who are currently displaced, regardless of how many times they have been displaced. Data source: Internal Displacement Monitoring Centre (2026) OurWorldinData.org/migration | CC BY
You may wonder how come there are internally displaced people in countries such as Japan and the United States. The reason is that natural disasters can also be a source of internal displacement. In fact, my in-laws were internally displaced persons after a tornado devastated our neighborhood in Dallas in October 2019. Notice that the Africa is where you have most of the internally displaced persons.
Where are the Refugees ?
Refugees by country of asylum, 1951 to 2024. People who fled their country of origin because of serious threats against which the authorities of their home country cannot or will not protect them. This includes all refugees, not just those who arrived that year. Data source UNHCR (2025). OurWorldinData.org/migration | CC BY
The three countries with the most refugees are Iran (3.49 million), Turkey (2.94 million) and Germany (2.75 million). Next comes Uganda, Pakistan, Chad, Poland, Ethiopia, all Bangladesh, all with more than one million refugees. Iran has a lot of refugees because of the refugees from Afghanistan pouring into the country, and Turkey has a lot of refugees because of the refugees from Syria, and Germany has a lot of refugees because of their generous immigration and refugee policy. The big spike in the number of refugees in Iran around 1991 was due to the Gulf war and the Afghanistan war.
As for other Western countries, France has 722 thousand refugees, United Kingdom 516 thousand refugees, the United States 435 thousand refugees, and Spain 429 thousand refugees. By clicking here, you can play around with the graphs and compare all countries in the world.
Superfact 117: The share of electricity generated from Solar Power in the world has grown from essentially 0% in the year 2000, 0.15% in 2010, to 3.19% in 2020, and to 8.75% in 2025. Both wind and solar energy are expanding fast around the world, but solar energy is a strong latecomer to the energy scene.
Solar energy panel. Shutterstock asset id: 2459435149 by Nordic Studio.
In the year 2000 less than 0.01% of the world’s electricity was generated by solar. In 2005 it was 0.02%, in 2010 it was 0.15%, in 2015 it was 1.07%, 2020 it was 3.19%, in 2025 it was 8.75%. Can you guess what will it will be in 2030? The United States may be behind the rest of the world with respect to wind power and EVs, but it closely follows the rest of world when it is about solar. You can play around with the graph below and select different countries by clicking here.
Share of electricity from Solar. Measured as a percentage of total electricity produced in the country or region. Data source: Ember (2026): Energy Institute – Statistical Review of World Energy (2025) OurWorldinData.org/energy | CC BYLow carbon sources met all of 2025’s electricity demand growth. Change in global electricity generation by source, 2024 to 2025. Total generation rose by 850 terawatt-hours (TWh). Note: “Other renewables” include hydropower, bioenergy, tidal and geothermal. Data source: Ember (2026). This graph comes from this page.
New solar panel technology such as Perovskite Solar cells is being developed. The price of lithium-ion batteries has fallen by 99% since 1991 and by 82% in the last ten years. New battery technology such as sodium-ion batteries is being developed. One advantage of sodium-ion batteries is that they function exactly like a lithium-ion battery but replace lithium with abundant sodium ions to carry the electric charge. The evolving battery technology makes it easier to store power from solar during the night. SolarPower Europe project that the global solar fleet will more than double by 2030. In other words, the future looks bright for solar power, and that pun was intended.
Three different scenarios / projections by SolarPower Europe. The medium scenario predicts slightly more than a doubling of global solar fleet from 2026 to 2030.
Solar Power as a Share of Electricity Generation Around the World
For solar, the United States follows the rest of the world closely. Some countries have a higher percentage, such as the Cook Islands – 50%, Luxembourg – 30.52%, Chile – 25.06%. If you wish you can take a closer look here, or here, and you can play around with the different graphs. You can pick millions of combinations of countries and regions. For illustrative purposes I am showing some combinations below.
Share of electricity production from solar. Measured as a percentage of total electricity in the country or region. Some countries utilize solar more than other countries. These graphs include, Cook Islands, Luxembourg, Chile, Greece, Spain, Netherlands, Australia, Germany, the World and the United States. Data source: Ember (2026); Energy Institute – Statistical Review of World Energy (2025) OurWorldinData.org/energy | CC BYThis graph shows that China has expanded their share of solar power a bit faster than the rest of the world. The share of electricity generated from Solar Power in the world was 8.75% in 2025 and in China 11.1%. Share of electricity production from solar. Measure as a percentage of total electricity in the country or region. Data source: Ember (2026); Energy Institute – Statistical Review of World Energy (2025) OurWorldinData.org/energy | CC BYThis graph shows the share of electricity generated from Solar Power in the largest countries and economic regions in the world. The share of electricity generated from Solar Power in the EU was 13.13% in 2025, in China 11.1%, in India 9.42%, in the World 8.75%, and in the US 8.6%. Data source: Ember (2026); Energy Institute – Statistical Review of World Energy (2025) OurWorldinData.org/energy | CC BY
How Clean and Safe is Solar Energy ?
You sometimes come across claims that renewable energy isn’t really clean energy. The truth is that renewable energy such as wind, solar, etc., is much cleaner than gas, oil, and coal. These energy sources are also much safer and using them saves a lot of lives. As you can see, among the eight energy sources depicted solar is the safest, and among the cleanest. Coal has 1,230 times higher death rate than solar. According to the Energy Policy Institute at the University of Chicago Chinese citizens can expect to live on average 2.2 years longer than they would have a decade ago, due to the sharp drop in pollution. This is thanks to the increased use of EVs and renewables such as solar.
Greenhouse gas emissions and death rates from various sources of energy. Fossil fuels and biomass are based on state-of-the art plants with pollution control in Europe and are based on older models of the impacts of air pollution on health. This means that these death rates are likely to be very conservative. The graph shows that renewables and nuclear energy are the cleanest and safest forms of energy. For further discussion see the article: OurWorldinData.org/safest-sources-of-energy. Electricity shares are given for 2021. Data sources: Markandya & Wilkinson (2007); UNSCEAR (2008: 2018); Sovacol et al. (2016); IPCC AR5 (2014); UNECE (2022); Ember Energy (2001). OurWorldinData.org – Research and data to make progress against the world’s largest problems. Licensed under CC-BY by the authors Hannah Ritchie and Max Roser. Citation : Hannah Ritchie (2020) – “What are the safest and cleanest sources of energy?” Published online at OurWorldinData.org. Retrieved from: ‘https://archive.ourworldindata.org/20260202-100556/safest-sources-of-energy.html‘ [Online Resource] (archived on February 2, 2026).
Below are two pictures corresponding to zoom-in of the graph above.
Death rates from accidents and air pollution. Measured as deaths per terawatt-hour of electricity production. 1 terawatt-hour is the annual electricity consumption of 150,000 people in the EU. The graph shows that coal, oil, gas, and biomass are a lot deadlier than hydropower, wind, nuclear power, and solar.Greenhouse gas emissions. Measured in emissions of CO2 per gigawatt-hour of electricity over the lifecycle of the power plant. 1 gigawatt-hour is the annual electricity consumption of 150 people in the EU. The graph shows that coal, oil, gas, and biomass are responsible for a lot more greenhouse gas emissions than hydropower, wind, nuclear power, and solar.
Important Climate and Energy Facts
As I said, the misinformation about climate science has bamboozled a lot of people. We know that climate change / global warming is happening. We have also known for several decades that the current climate change / global warming is not natural. It is caused by us, chiefly due to the burning of fossil fuels. Yet many non-scientists dispute it.
The scientific evidence is conclusive, but a lot of people know very little about the evidence. It includes satellites directly measuring our greenhouse gases trapping heat, the upper troposphere is cooling whilst the lower atmosphere is warming, showing that the heating is from greenhouse gases, the unnatural speed of the warming is another piece of evidence, isotope studies, climate models, etc. Below are fourteen super facts related to climate science and clean energy.
Superfact 116: Time and space do not exist for light particles (called photons) and not for other particles without mass either. All massless particles travel at the speed c = 299,792,458 meters per second compared to all other objects regardless of how fast those other objects are moving. Objects / particles that have mass will always travel slower than c = 299,792,458 meters per second. The speed of light, c, is not really a speed. It is a conversion factor between space and time. It is therefore a universal constant.
Billions of photons coming into the eye. Shutterstock asset id: 2629068895 by muratart.
Light does not travel through a medium, like a sound wave, or a water wave does. There is no medium for light to travel in. Photons are massless, which means that an extremely tiny force, an infinitesimal smallest possible force, could send a photon off at infinite speed. There is no mass to hold the photon back.
However, the conversion factor between space and time c = 299,792,458 meters per second will prevent that and the photon will travel at this “speed”. Since c is a conversion factor, a physical constant describing time and space, this is not motion, or movement, in a normal sense. Space and time won’t allow any physical event to have any effect faster, and no information of any kind can travel faster than c = 299,792,458 meters per second.
This means that from the photon’s perspective there will be no time at all. A photon, or a light beam, will travel from Earth to a distant galaxy a billion light years away in an instant. It will not take a billion years. It will not take one year. It will not take one second. It will not take one microsecond. It will not take a nanosecond, or a picosecond, or a trillionth of a picosecond. It will take zero seconds. The Big Bang and the end of the Universe (if there is one) happen at the same exact moment to a photon. Time does not exist for a photon (or a gluon, or any other mass-less particle).
This is a mind-blowing fact, and it is true and important to our understanding of the Universe. Therefore, I consider it a super fact.
What does the Speed of Light Being a Universal Constant Mean ?
Four rockets, A, B, C, and D, are traveling along a light (laser) beam. No matter how fast they travel along the light beam, the light beam will always travel c = 299,792,458 meters per second faster than they do. I generated this picture with the help of ChatGPT.
The first thing to acknowledge about the speed of light (in vacuum) is that it is a universal constant as explained in my post “The Speed of Light in Vacuum Is a Universal Constant”. However, I am explaining this fact slightly differently in the next few paragraphs with the help of the picture above.
In the picture above we are emitting a light beam from our spaceship using our super laser. There are also four rockets that travel along the light beam. The rocket on the lower right (rocket A) travel at 1% of the speed of light v = 2,997,924.5 meters per second (or 2,998 miles per second). That is extremely fast, but much slower than light. You would think that the light beam would travel a little bit slower compared to this rocket at the relative speed c – v = 299,792,458 – 2,997,924.5 = 296,794,533.5 meters per second. But it doesn’t. The light beam is still speeding ahead of rocket A at exactly c = 299,792,458 meters per second.
What happens if you compare the beam with the rocket in the lower left (rocket B)? That rocket travels at 10% the speed of the light beam. Shouldn’t the light beam move 10% slower compared to that rocket? No, the light beam speeds ahead at exactly c = 299,792,458 meters per second compared to rocket B, once again.
Now take rocket C in the upper right corner. It also travels along the light beam but at half the speed of light. Shouldn’t the light beam travel at half of the speed of light compared to rocket C? No, it will stubbornly travel at exactly c = 299,792,458 meters per second compared to rocket C. Not less and not more.
The same is true for the rocket in the upper left, rocket D. It travels at 99.99% of the light speed compared to us in the spaceship, and yet the light beam will stubbornly travel at exactly c = 299,792,458 meters per second compared to rocket D. Not less and not more.
The universal speed c = 299,792,458 meters per second is not so much about light. As mentioned, it is a conversion factor between space and time. You take this conversion factor with you everywhere you go and regardless of how fast you move. That’s the way time and space works.
The fact that the speed of light is a universal constant that is exactly the same for all observers, no matter how fast they move, should tell you that it is not a speed in a normal sense. It is not really a “speed” at all. As mentioned, it is a conversion factor between space and time. Light isn’t really travelling super-fast. It is just conforming to the geometric reality of time and space, and to us it looks like it is travelling at the speed c = 299,792,458 meters per second.
The Space-Time Interval for Light is Zero
I mentioned that from the photons perspective time does not exist but that from our perspective light travel through space or seem to travel through space and that takes time. However, for us space and time are separate things. If you combine them and measure space-time intervals instead you get a more complete picture. In 3D space you get the distance between two points by adding the differences between the coordinates using Pythagoras theorem, s^{2}=x^{2}+y^{2}+z^{2}. (x, y, and z, are differences in the coordinates) As long as you are consistent with the units you will always get the same distance regardless of position and orientation of your coordinate system. You can read more here.
If you add time to Pythagoras theorem you will get the space-time interval, which interestingly enough is the same for all observers. There is no time dilation or length contraction in the interval. s^{2}=x^{2}+y^{2}+z^{2}+(it)^{2} As you might suspect, intervals involving light travelling from one event to another will always be zero for all observers, and not just from the photons perspective. And again, the same applies to all massless particles. Below are the Pythagoras formulas for different versions of the interval. In the top picture it is assumed that the conversion factor c = 299,792,458 meters per second has already been baked into to the time variable and in the bottom it has not. This is not any stranger than converting feet to meters.
The three formulas for the spacetime interval above all assume that the unit used for time is the time it takes light in vacuum to travel the distance unit used. If that is meters, it would be the time it takes light to travel one meter. The top formula is the Euclidian form of spacetime. It contains only the ‘+’ operator at the expense of adding the imaginary number (square root of -1) in front of the time coordinate. The second form is typically used with time like intervals and considered the standard form. The third form is used when the distance between two events is larger than the time distance, or distance like intervals.If you measure the space coordinates in meters and the time in seconds you must adjust the units to match by inserting the speed of light in vacuum c = 299,792,458. The three forms of the space interval now have the constant c attached to the time coordinate.
What about the speed of light in water ?
It is well known that the speed of light in transparent materials such as water and glass is slower than the speed of light in vacuum. The speed of light it water is about 75% of the speed in vacuum and about 70% or less in glass (depending of the type of glass) compared to the speed in vacuum. In some materials the speed of light can be much less than that. This seems to violate what I said above about the speed of light always moving at c = 299,792,458 meters per second for all observers regardless of their speed.
What is going on is that when light moves through matter it is being absorbed and emitted as it “travels” between the atoms in the material, and this absorption and emittance process takes time. This time is extremely short but long enough to be measurable. As the photons move in between the atoms they travel at the “speed” c = 299,792,458 meters per second, the time to space conversion factor I’ve been talking about. See the illustration below.
From ground state to excited state, absorption and emission of a photon in an atom. Shutterstock asset id: 2180385419 by rktz.
More about the mass of a Photon
I’ve said photons have no mass. According to Einstein’s theory of special relativity, time does not pass (or effectively “exist”) from the perspective of a massless particle. However, this is the intrinsic mass or so called proper mass or invariant mass. It is the mass of an object as measured by an observer who is completely at rest relative to it. This intrinsic mass is the mass that a photon does not have.
The mass of an electron is 511 Kilo Electron Volts, which is 0.0000000000000000000000000009109 grams. That is the intrinsic mass of the electron. If an electron is sped up to close the speed of light its mass increases and goes toward infinity. If its speed is very close to the speed of light its mass could be much bigger than that of the entire Universe. That’s because as you are increasing the speed of the electron, you are increasing its kinetic energy and as you increase the total energy of the electron you also increase its total mass according to E = mc2.
As the electron’s speed approaches the speed of light the kinetic energy goes toward infinity. That is one reason why it is impossible to travel at exactly the speed of light for anything but massless particles. Infinite energy and infinite mass are not realistic. We, the objects that have mass, can move closer and closer to light speed but never get there.
However, the intrinsic mass for photons is zero and therefore the photon is travelling at exactly the speed of light, c = 299,792,458 meters per second. E = mc2 still applies to light but the mass is not the intrinsic mass, which is zero, but the total mass, and the total mass can pretty much take on any number.
What about Warp Drives ?
So, nothing with mass can travel at the speed of light, and nothing can exceed it. What about the warp drive in Star Trek? As I said, the speed of light is not really a speed but the conversion factor between time and space. It is a geometric fact of space-time. That is a pretty difficult reality to get around, just like it is pretty difficult to push Earth out of its orbit by pushing on the floor. However, there is a way to cheat and that is to stretch space-time itself. This is theoretically possible, but it requires colossal amounts of mass-energy and enormous amounts of negative energy. We don’t even know if negative energy exists on a macroscopic scale.
So, no one knows if a warp drive is possible, and if it isn’t, then we are stuck moving slower than the speed of light, which would make interstellar travel very difficult and inconvenient.
Richard Feyman’s Lecture on Why Light Is NOT Moving Through Space?
The YouTube video below is very long, 48 minutes. However, Richard Feyman, Nobel prize winner in physics, has a knack for explaining extremely abstract concepts so that they are easy to understand. If you are very interested in this topic and have some extra time, this is a fascinating lecture. He certainly explains this topic better than I can.
Super Facts 