While the five planets visible to the naked eye have been known for almost all of astronomy’s history, it was not until the discovery of Uranus in 1781 by Sir William Herschel that astronomers began searching for other planets in our Solar System. After Neptune was discovered in 1846, astronomers began turning their telescopes towards the sun in search of another planet, seeking to explain Mercury’s strange behavior. It had been known for some time that Mercury’s orbit precessed slowly over time, and in 1859 French mathematician Urbain Le Verrier predicted that there must be another small planet even closer to the Sun whose gravity caused the odd motion. While many astronomers searched for Vulcan over the coming years, no truly confirmed sightings were ever made (as it does not exist) and Mercury’s orbital precession was eventually explained as a relativistic effect of the Sun.
Nearly every component of our body and the planet we call home was created inside stars. Heavy atoms like carbon, nitrogen, and oxygen are produced from lighter elements like hydrogen and helium through the nuclear fusion process that takes place in stars. These substances are released into space when a star undergoes a supernova explosion after its life as seen in this image. The immense clouds of gas and dust between stars are known as the interstellar medium, including the fragments left over from these explosions. Eventually, gravity causes these clouds to collapse, forming new stars and planets. And because these clouds contain elements like carbon and nitrogen, which are essential for life as we know it, the planets that form around these stars can also support life.
So, in a genuine sense, we are made of the same material that stars are made of. The carbon in our DNA, the calcium in our bones, and the iron in our blood were all forged in the fiery hearts of stars that exploded billions of years ago. It’s a humbling thought but also a reminder of our connection to the universe around us. We are not separate from the cosmos but rather a part of it. And that’s something worth celebrating.
With our totally unrestricted guidelines on Blog 4, I would like to make a bit of a deviation from the content of our course and discuss time dilation and the theory of relativity!
When I first learned about time dilation, which refers to the difference in elapsed time as measured by different clocks due to different relative velocities of the clocks or different gravities acting on the clocks, I couldn’t wrap my brain around it. Time dilation hinges on the idea that time is not a universal constant, rather, the speed of light is constant. This is extremely difficult to understand on Earth–we have no firsthand experience with anything other than the perceived constant, slow march of time steadily ahead. I could not understand how the speed of a photon exiting a flashlight held by a person at rest could possibly be the same as for a photon exiting a flashlight held by a person riding a bike–obviously speeds are additive!
In fact they are not–not where relativistic speeds are concerned. The speed of light is a universal speed limit, no object can move faster. What finally helped me understand this was a YouTube video, which explains a couple of Albert Einstein‘s thought experiments. I would like to explain it here!
While riding the train home from his job as a clerk, Einstein looked at a clocktower behind him, receding into the distance. He could see the second hand ticking as time passed and he moved further away. He thought–what if this train was moving at the speed of light? The clock hand would appear to be still–photons must travel from an object to your eye for you to be able to see it, and if you are moving away from the photon as fast as it is moving toward you, it will never reach your eye. The clock hand would appear frozen in time, even though the clock would still appear to tick away from the perspective of someone standing next to the clock. (Note: technically time can’t be “frozen”–since no object can actually travel at the speed of light, we must settle for very close to the speed of light, so the clock hand will still move very slowly.)
How can this be possible? Isaac Newton‘s laws of motion state that velocities are never absolute, but must be described in relation to something else. For example, a car may travel 60 mph with respect to a person standing on the side of the road, but it will appear to travel 40 mph with respect to a person in a car traveling 20 mph in the same direction. It will appear to travel 80 mph with respect to a person in a car traveling 20 mph in the opposite direction. However, James Clark Maxwell found experimentally that the speed of light is fixed, regardless of who is observing it.
These two ideas are, on the surface, contradicting. How can the speed of light be constant, if speeds must be measured relative to some other object?
Einstein’s solution was to make a small adjustment to Newton’s laws, while still upholding the constancy of the speed of light. He proposed that time must slow down for objects traveling at great speeds, in order to keep the speed of light constant. This was called time dilation–time does not move steadily forward, but can stretch and contract with varying velocity of motion. It is important to note that Newton’s laws still work for non-relativistic situations, which is why we haven’t completely thrown them out!
To accommodate time dilation, Einstein further developed the concept of spacetime–the idea that time and space are not separate entities, but are inextricably intertwined into one entity. Gravity causes distortions of spacetime–this can be imagined as 3D dips in a 2D “fabric” of spacetime, meant to represent the actual 4D spacetime. Smaller objects orbit around larger ones since they are caught in the curved dip of spacetime around the larger object.
We know that the force of gravity on an object increases with decreasing distance from another object–most noticeably if a small object is approaching a larger one. This difference in forces represents a difference in accelerations–imagine a person falling faster as they approach the Earth. Now, consider what we just learned–that the faster you move through space, the slower you move through time. A clock in high-Earth orbit around will tick faster than the clock on your desk, since the gravitational forces, and thus accelerations, on the two are different.
We can look at another thought experiment to understand why this is so. Imagine a person falling from high-Earth orbit down to the ground, carrying a photon clock–a theoretical clock for which it takes one second for a photon to bounce between two reflective surfaces. Another observer stands on the ground. What will they observe as the person falls from space?
The falling person will see the light from their own clock traveling in a straight line back and forth, much like when you throw a ball upward and catch it while traveling in a car–it doesn’t move behind your head. On the other hand, the observer will see the light traveling in diagonal lines, much like if an observer outside the car were to see you throwing the ball up and down. The net movement of the ball, or the photon, would appear to be a zig-zag.
What does this mean for our clock? Light is observed by the person on Earth to travel a greater distance–the diagonal lines are longer than the straight ones. Since the speed of light is constant, and the confines of the start and the end of the event are the same, this must mean that time has gotten shorter. The duration of a second is not constant–it is proportional to the velocity of the object in motion.
This has been experimentally proven–time records of clocks on spaceships that have spent a decent amount of time in space are different from time records of the same “event” as measured by clocks on Earth. Time passes at different speeds, and thus the total amount of time elapsed is different.
We have explored here time dilation and the theory of relativity–the idea that if the speed of light is constant, which has been repeatedly proven to be true, then time must not be constant in order to compensate for light traveling different distances based on motion and gravity. Thank you all for sticking around, and if you never understood Interstellar, I hope this explanation helps!
Dark Matter is a fascinating topic, yet we know so little about it. Regardless, a good amount of evidence exists that indicates dark matter is real. One pertains to the flatness of rotation curves for spiral galaxies at extended distances. The graph does not drop off, but rather, continues in (essentially) a flat rotation curve, indicating the presence of much more mass and therefore large amounts of dark matter.
We can also find more evidence for dark matter by measuring the velocities of galaxies within a galaxy cluster from their Doppler Shifts. The mass we calculate is roughly 50 times greater than the mass of all the stars in that galaxy cluster! The 3rd line of evidence also has to do with galaxy clusters. Clusters contain great amounts of X-Ray emitting hot gas (since they have a strong gravitational ability to hoard large amounts of interstellar gas). The temperature of this hot gas (which we infer from particle motions) reveals the mass of the galaxy cluster. Estimates conclude that ~85% of galaxy clusters are Dark Matter, with the rest being gas and stars. We can use Gravitational Lensing (the warping of light rays by gravity over large distances) to discern a cluster’s mass.
So what options are astronomers left with regarding dark matter? Well, either dark matter really does exist, and we are seeing the evidence of its gravitational attraction, or something is horribly wrong with our understanding of gravity, causing us to erroneously surmise that dark matter exists. However, because gravity is so well tested, most astronomers agree that dark matter is real.
Based on Einstein’s theory of relativity, black holes have a theoretical opposite know as “white holes”. Rather than it being impossible for matter to exit (as is the case with black holes), it would be impossible for matter to enter a white hole. Physically, it would look very similar to a black hole: the only difference would be matter being ejected from the horizon. A white hole is both a black hole’s twin and its opposite.
Black holes exist largely on the edge of our understanding of physics, and the idea of white holes can be used to explain some of the inconsistencies we see. For example, black holes leak energy, implying that one day they may disappear entirely. If that occurs, we have no theoretical explanation for what happens to the matter that has entered the black hole that doesn’t violate the laws of physics. One explanation would be that a white hole forms upon the death of a black hole.
Unfortunately, no white hole has ever been observed, and there are still many practical barriers to them even existing. Black holes are formed by a star collapsing in on itself, but the opposite–a star forming from an event horizon–violates laws of entropy. Furthermore, if a white hole was constantly ejecting matter into its orbit, the collisions would eventually cause a collapse back into a black hole. So, while the idea of a white hole is interesting and would answer unanswered questions about black holes, odds are low they really exist, or if they do, don’t stay alive for long.
Climate Change is one of the most important issues that has already affected our lives and one that threatens our future. To get an understanding we need to look back in history to when human’s began to cause a shift in the climate. In the 1800s, humans began the industrial revolution thus having to burn tons of coal, natural gases, and oil in order to generate electricity and power our various machines. Due to us burning these tons of fossil fuels since than we have added extreme amounts of CO2 and other greenhouse gases into the atmosphere. These greenhouse gases stop heat from escaping the earth into space, thus with the amount we have generated over the last few centuries we have been trapping too much heat than what is natural for the world. According to data, the planet is already 1.8 degrees Fahrenheit hotter than it was in the 1880s and this will only continue to rise as we burn more and more. For the future if we do not keep this in check there is evidence that sea levels will rise, flooding could occur in large cities, hurricanes will become stronger, and many more. We still have time to prevent this and everyone has the ability to do their part to secure our planet’s future. People who deny climate change exist are truly ignorant and will continue to further this problem, which is why its crucial to educate the next generations so that they are equipped to tackle the challenges that lie ahead.
Many scientific theories attempted to explain the source of the Sun’s energy, and the very first hypothesis involved some explanation pertaining to chemical reactions and gravitational collapse. Chemical burning, however, was ruled since no chemically burning substance like wood or gasoline can account for the Sun’s enormous luminosity. As for gravitational collapse, the conversion of gravitational potential energy into heat would only allow the Sun to shine (produce enough energy) for 25 million years. This theory was scratched thanks to geological research, which proved that the Earth is much older than that (~4.5 million years).
Ultimately it was the development of nuclear theory that revealed the truth. The Sun generates immense amounts of energy from nuclear fusion reactions in its core. When Hydrogen is converted into Helium, some mass is lost in the process. This fraction of mass is transferred into energy. This amount of energy is identified by Einstein’s equation: E=mc^2. Due to the innumerable amount of reactions taking place every second and the Sun’s large mass, nuclear fusion will provide enough energy for the Sun to shine for 10 billion years. So don’t worry about the Sun running out of power anytime soon.
The atmosphere is split into four different layers: the troposphere, the stratosphere, the thermosphere, and the exosphere. The troposphere is the lowest layer and is where greenhouse gasses absorb the infrared light and where storms occur. The stratosphere absorbs solar ultraviolet light by ozone, Earth is the only planet to have this layer. The thermosphere absorbs x-rays and makes radio communication possible. The exosphere is the fuzzy boundary between the atmosphere and space.
Just as all things have a beginning, all things have an end. Unfortunately this applies to our Sun as well. As a kid, I used to think that the Sun was basically just like a lamp light in the sky. When a lamp runs out of batteries, all you have to do to make it shine again is replace its light bulb. This is not the case with the Sun. Our Sun has been burning brightly for about 5 billion years (that’s an extremely long time!). The Sun is expected to burn for a total of 10 billion years, so it’s about halfway through it’s life-cycle. The looming question is: “what will happen to the Sun and our solar system when the Sun dies”?
Originally, scientists believed that it would turn into a bubble of cosmic dust and gas. In order for that to happen though, the sun would have to be a bit more massive than it currently is. In about 5 billion years when the Sun uses up all of its nuclear fuel, it will turn into a red giant. Both Mercury and Venus will be swallowed and the Earth will be burnt to a crisp. It’s core will begin to shrink and then eject its outer layers to engulf everything to the outer layer of Mars. Fortunately, or unfortunately, we won’t be around to see all of this happen. Humans are actually only expected to live for about 1 billion more years because the Sun is gradually increasing in brightness. The Earth’s surface will eventually become so hot that it will be impossible for water to form. But until that time comes, humans are on the search for a new home in order to keep humanity alive!
You can find more information about what the end of our Sun’s life looks like here. If you need some more convincing from some professionals, here is a website where some scientists talk about the Sun’s end.
The Trappist 1 system is a collection of seven rocky worlds that orbit an ultra cool dwarf star which was named 2MASS J23062928-0502285 at the time of its discovery because of the telescope used. All of the worlds in Trappist 1 are Earth-like meaning it contains the same elements like iron, oxygen, magnesium, etc; however, it is assumed they are in different ratios because the masses of all seven are lighter than the mass of Earth. They are all likely to have liquid water, and the most Earth-like planet of this system is Trappist 1-E (the fourth planet from the central star).
My interest in this system mainly stems from my love for astrobiology – the study of life on other planets – because of the sheer amounts of evidence collected suggesting 1-E is like Earth. Trappist 1E lies in the habitable zone of its central star just like Earth does. Coupled with the fact that there’s liquid water, this means there is a possibility for life to survive with the right temperatures from the stars and evolve like microorganisms did millions of years ago on Earth.
This system was discovered rather recently, and it’s only around 40 light years away; so, it will be super interesting to see what we discover in the ever evolving realm of science!!
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