Mastery is achieved when “telling time”
becomes “telling time what to do.”
~“Telling Time”
This week I’m trying something a little different. I heard about a contest where the goal was to explain time in terms an eleven-year-old could understand. While I didn’t make the contest deadline, I thought I’d share my attempt with you all.
What Is Time?
What is time? Scientists often think of time as a direction you can travel in. Just as we can move up, down, left, or right in space, we can move in time. Something is wrong with this comparison, though. When you walk forward two steps, you can turn around and walk backwards two steps, too, and get back where you started. Time is different. If you wait twenty-four hours to travel to tomorrow, there’s no way to turn around and travel back a day to where you started. This irreversibility is called the arrow of time. So what makes time different from space?
The Law Of Legos
Say you really like Legos. (Or imagine one of your friends who does. You probably have one—Legos are pretty cool!) So you build a really nice Lego castle. It’s so nice that you decide to keep it on display on the kitchen table. Over time, your friends come by and admire it. Your mom admires it, too, but she’s a little clumsy and she breaks a tower off. So you dig around in your collection, find some pieces to help repair your castle, and you fix it.
Your castle stays on display for a while, and sometimes people accidentally bump into it or push on it too hard. Each time it breaks, you dig through your collection to find the remaining pieces to fix it. But since you’re very eager to fix your castle, each time you go through your collection, you leave it a little bit more disorganized.
No matter what happens, your Lego collection will always become less organized. To prevent your castle from decaying, you have to make the rest of your collection messier. Scientists have a fancy name for messiness: entropy. Over time, the total entropy of the universe never decreases. In other words, things can only get messier. You can trade entropy from one place to another, like when you fix your castle (decreasing entropy) by going through the rest of your collection (increasing entropy), but the total entropy of the whole collection will still increase. Scientists call this the Second Law of Thermodynamics.
Legos and Time
Earlier we asked what makes time different from space. Why can you go into the future but not the past? Since the universe, like your Lego collection, obeys the Second Law, it’s always getting messier and never getting neater. Because both neatness and time can’t go in reverse—you can’t get neater and you can’t go to yesterday—scientists think that the Second Law is actually what makes time irreversible. If you went back in time, it would fix your Lego castle without messing up the rest of your collection, so that your collection as a whole would get less messy. Since this would break the Second Law, you can’t go back in time!
Telling Time
Even after you know why you can’t travel into the past, time is still pretty confusing. We measure space as a distance, with rulers and meter-sticks (or yardsticks). If time is a direction, just like forward or up, we should be able to measure a distance in time. But we measure time with clocks. What’s going on? Fortunately, we have a very nice way of measuring time with a meter-stick. The secret is light.
Light is a funny thing—it’s very shy. If you’re chasing a beam of light and you speed up to try to catch it, the light will speed up the exact same amount! No matter how fast you go, the light speeds up to stay ahead of you, so that the difference between your speeds is always the same. This is why we say the speed of light is constant: it is always going faster than you by a constant amount. Because light always goes this same speed more than you, you always know its speed (300,000,000 meters per second, in fact—whew!), so you can use its speed to figure out how to measure time with a meter-stick. A distance in time is the amount of time it takes light to travel that distance in space. For example, we can talk about a “second” as the time it takes for light to travel 300,000,000 meters, instead of going around in circles saying, “Well, a second is just…a second, you know?”
Deceptively Simple
So what did we discover? We looked at a clock, which only goes forward and never backward, and we asked, “Why does it do that? What is time?” By thinking about Legos and light, we discovered that time is a direction, just like forward, backward, left, and right. But it’s not quite like a direction in space. There’s something else. We can’t go back in time because it would make the universe a neater, tidier place, and this is impossible—the universe always gets messier. Such a simple question and such a complicated answer! This is how physics always works. Scientists ask simple questions, but we often find that the simpler a question is, the harder it is to answer. But when you find a really nice answer to a really hard, simple question, it’s very fun and very cool. This is why I love my job. I hope you’ll love learning more about it!
Good job! I like the inclusion of entropy.
I had an entry planned, based on a the rotation in velocity space topic we discussed few weeks ago. Sadly, I ran out of time, (pun intended). The interpretation of a Lorentz contraction as a rotation wasn’t shared by many, if any professors, and while I kept coming across references that discussed contraction as a rotation, (Sommerfeld for example), they always had a ‘well, not really’ tone to them. Consequently, I’m still doing research on the subject.
Thanks, Hamilton! Glad you like it! I look forward to your post on rotation.I believe Carrol briefly mentiosn lorentz transformations as rotation in his text book if you haven’t investigated him yet.
I really liked the way you tried to make TIME simpler.Would you please try and answer a question of mine? It is just an opinion of mine which i shall try to present in the form of a question.The answer would be as simple as a “yes” or a “no”. According to you,(according to the 2nd law of thermodynamics,to be more precise)things keep getting messier as they move forward in time-which is always.Now,i have just read on another website that the theory of evolution is incorrect because evolution is defined as the process by which life undergoes increase in complexity(and continues to become better and better). The website said that this is not possible, because the second law of Thermodynamics and the evolution theory are totally incompatible. But, i disagree.i believe that if some energy is utilized, a natural and automatic process can be reversed.Eg:i have learned in bio that “osmosis is a process of diffusion of water molecules across a semi permiable membrane FROM THE HIGHER CONCENTRATION OF WATER MOLECULES TO THE LOWER CONCENTRATION OF WATER MOLECULES.”But i have also learned that the reverse of this process occurs(MOVEMENT OF WATER MOLECULES FROM LOWER TO HIGHER CONCENTRATION) utilizing energy from the cells.This is called as the ACTIVE TRANSPORT and is a contributing factor for the ascent of plant sap.In this way, life, using energy, DEFIES THE K+ ion CONCENTRATION THEORY AND THE SUGAR CONCENTRATION THEORY.Though physics says the water molecules will only diffuse toward the lower concentration, life uses energy to make the reverse happen.Why, then , does the 2nd law denies that life may evolve and get better and better by using additional energy to make the reverse happen?Anyway the 2nd of Thermodynamics law says that every thing keeps decreasing in order WHEN IT IS LEFT ON ITS OWN!Doesn’t that mean that it could be overcome by life because it is constantly generating usable energy and is never “left on its own(with no energy acting on it anymore)”?
Pseudonymous,
Entropy in the entire universe always increases. But the entropy can be moved around. So when we expend energy to create order—which we absolutely can do—we create entropy elsewhere in the universe.
In other words, there’s nothing wrong with living things emerging naturally. The second law absolutely allows it. However, the cost is that by ordering ourselves, we living things are causing disorder around us. Let’s think about what “eating” means. We take a structure of molecules and we destroy it to get the energy out of it. This let’s us keep our own structure and our own order. But in the process, we cause disorder to our food source. The principle goes all the way down. Photosynthesizing bacteria extract order from the sun and from the carbon dioxide they absorb.
So evolution and thermodynamics get along just fine.
Does this help?
Perfectly well.
So can i safely conclude that the website was wrong saying that evolution and thermodynamics are incompatible?
And the website also said that there is an Almighty omnipotent creator who created the universe, because the evolution theory does not explain how everything was created.Jonah, what is your opinion about how the universe was created?I know the process of the formation of the sun, how it would end, and how the planets and all were created(isn’t it the nebula thing?)But please tell me how, basically, the very first atom came into existence.
I mean if it would have always been, the radioactive elements would all have become lead by now, wouldn’t they?The universe was probably formed at some point of time.How?
Pseudonymous,
Sorry for the late reply. Yes, you can safely conclude the website is wrong. Evolution and thermodynamics are compatible.
Thanks to the humungous triumphs of modern astronomy, we know pretty well how the first atom was formed.
We know that the universe is expanding and, indeed accelerating. (I wrote an article about this, actually: http://www.thephysicsmill.com/2013/03/24/receding-horizons-dark-energy-and-the-expanding-universe/). So we know that deep in the past, the universe was very dense and very hot. (The denser something is, the hotter it gets.)
(Before this point in time, we don’t really know what happened. We believe that the universe started as a point and expanded in a single catastrophic explosion called the “big bang.” But we don’t know for sure. A process called “cosmic inflation” erases evidence of what happened too far in the past. I wrote some articles about this. The first is here: http://www.thephysicsmill.com/2013/06/09/a-mess-of-cosmic-coincidences-problems-with-big-bang/ and the second is here: http://www.thephysicsmill.com/2013/06/26/fixing-the-early-universe-cosmic-inflation/)
In the dense, hot, past, atoms could not form. You see, the temperature of a gas actually corresponds to how fast the particles in the gas are moving. This means that every time an electron tried to bond with a proton, it was ripped apart by its own random high-speed motion.
When electrons are separated from protons, we call the gas a “plasma.”
This plasma was also full of light, because when charged particles move, they glow. The light couldn’t travel very far, because if it travelled very far, it would bounce off of one of the particles, but it was there.
But as the universe expanded, it cooled. And eventually an electron was able to bond with a proton, and the first hydrogen atom formed. Then the light was free to travel.
And the light has been travelling ever since. Over time as the universe expanded, it stretched out the wavelengths of the light so that super ultraviolet light eventually become red, then infrared, and then microwaves. But it’s still there. And if we look at the sky, no matter what way we look, we see empty space filled with this light, which we call the cosmic microwave background. (http://en.wikipedia.org/wiki/Cosmic_microwave_background)
So, I don’t know how the universe was created… but I do know how the first atom was formed. Does this help?
Oh! I didn’t finish answering your question! Radioactive elements formed much later than the early universe. After atoms formed, the universe was mostly filled with hydrogen. Over time, this condensed and formed stars.
In the core of a star, hydrogen atoms fuse with each other to form heavier elements. And then elements are released when the star explodes. We think that the first hydrogen formed about 377,000 years after the big bang, which was about 13.7 billion years ago. The first stars didn’t form until about 1 billion years after the big bang. Here’s the wikipedia article: http://en.wikipedia.org/wiki/History_of_the_universe
Pseudonymous,
we can’t say evolution is making organism better, evolution cannot be equated with progress.
every species has best body design according to their environment.
Thanks Jonah.Yes, all of it helped.But I’m still curious about how the universe formed and I’m not going to let go of the question in the name of the Creator!Atheism, you see.Never mind.Thank you!And yes-I’ve got to know recently that electrons and positrons materialize in vacuum.That could possibly have formed the universe.Where the electrons and positrons came from, is still a question.Any info regarding this is always welcomed.By the way, when a ray of light traveling in a rarer(say,air) medium strikes the denser medium surface(say,glass) when the ray is perpendicular to the surface, the ray passes undeviated.Why?
And yes-what does the speed of light in a medium & the optical density of the medium depend upon?
The story of the speed of light in a medium, and the bending of light at the interface–called refraction–is actually pretty long. So long in fact, I wrote an article about it. You can find it here:
http://www.thephysicsmill.com/2013/02/17/refraction-how-we-see-through-the-looking-glass/
In a nutshell, the speed of light in a medium depends on how freely electrons in that medium can move. Light is made up of electric and magnetic fields. And charged particles are affected by light and they affect it in turn. The more freely electrons can move, the slower light gets.
The reason that light bends at the interface between two mediums with different indexes of refraction is that, if it hits the new medium at an angle, some light hits the interface first and changes speed before the rest of the light. And if one side of the beam of light is travelling at a different speed than the other side, the light will bend. This is why the light doesn’t bend if the beam hits the interface perpendicular to it: the light changes speed at the same time everywhere in the beam.
Does this help?
We believe that the “inflationary period” of the universe is caused by a particle called the “inflaton.” We haven’t observed the inflaton yet… but that’s good, because otherwise the universe would still be inflating. Inflatons can come out of empty space the same way that electron-poistron pairs can–in a process called “vacuum fluctuation.” (We know that vacuum fluctuations occur through observation of the Casimir effect. Here’s the wikipedia article: https://en.wikipedia.org/wiki/Casimir_force)
If the inflaton fluctuates into existence, the universe will undergo a period of rapid expansion called an inflationary phase. At the end of inflation, the energy in the inflaton will be released to create ordinary matter like electrons and protons. It’s possible that our universe was formed this way.
The problem is that we can’t look back before the inflationary period. Say you take a balloon and inflate it just a tiny bit… enough so that you can draw on it. Then you take a sharpie marker and draw a face on it. But after drawing the face, you blow into the balloon some more and inflate it completely. Your drawing won’t look like a face anymore, because the ink will have been spread out. Instead, it will look like a bunch of dashed lines. This is what happens in cosmic inflation, but much more so. Any structure before inflation is lost because it is expanded so much that we can’t recognize it anymore. Indeed, since we are like an ant on the surface of the balloon, if we saw one dashed line leftover from the drawing of the face, the next dashed line might be so far away we can’t see it.
This is deep science here and I am really awestruck at such wisdom. But I totally understand that u can’t accept the creator theory so-to-say. Y should u, in the first place. But just think about what I’ll say now and don’t just push it away. Whether u believe It or not, there are humans that have a way of defying science or natural laws some magicians , Christians, so-called diabolic people. U may not believe what everyone says, but being an analytical person that u are consider that the is something definitely unknown. This people are engaging powers higher than our soul and intelligence without any physical technology so to say. There is a God and I’ve heard him speak. I’ve seen spirit beans and their interference. So many people cannot prove what they say that’s y u believe its all a theory. I can tell u what to say and do now and receive a strange visitation from the person u claim doesn’t exist. Just do a little research about Jesus in sincerity of heart…ask him if he is real as u sit in ur room. Much love.
Thank you Jonah!Yes it helped.I have a few doubts, though.If we have not examined the inflaton yet, how do we know that it exists?And are its properties known to us?Is the influx of space into the universe because of the inflatons?
Strictly speaking, we don’t know that inflation exists. We’re doing our best to try and understand it, but we don’t know yet.
The reason inflation was first proposed was to “fix” big bang theory. There’s nothing technically wrong with the theory, but there are some strange coincidences that physicists wanted resolved. Why do opposite sides of the sky look the same? And why is the universe, as far as we can tell, flat? Inflation answers these questions. My post on these issues has more information:
http://www.thephysicsmill.com/2013/06/09/a-mess-of-cosmic-coincidences-problems-with-big-bang/
As for why we should believe inflation as opposed to some other theory… that’s because of the predictions inflationary theory makes about the cosmic microwave background. You see, the inflation-causing particle, called the inflaton, obeys quantum mechanics. And it fluctuates just like other quantum particles. However, once the rapid expansion of the universe spreads these fluctuations out so far that flight can no longer pass from one end of the fluctuation to the other, it freezes and becomes permanent, because it can no longer communicate with itself. Later, when inflation stopped and the inflaton gave up its energy to create the other particles, these quantum fluctuations in the inflaton field became the seeds for galaxies and for the brightest spots in the cosmic microwave background.
That’s the idea, anyway. Before we understood the cosmic microwave background very well, physicists tried to predict what it would look like, assuming that the inflaton existed. And the predictions of inflation perfectly match what we see. This is why inflationary theory is generally accepted.
My post on inflation has a bit more information about this: http://www.thephysicsmill.com/2013/06/26/fixing-the-early-universe-cosmic-inflation/
But I want to emphasize that inflation is not well understood. It may have happened. It may not have. To fully understand inflation, we need a working theory of quantum gravity (how quantum mechanics and general relativity interact), which we don’t have yet.
Keep doubting, by the way. Skepticism is at the heart of science. Science only works correctly if scientists question what they are told, and try to see for themselves what the truth is… in a reproducible way.
Oh! And we believe the influx of space in the universe comes partly from inflatons and partly from dark energy. The inflaton isn’t directly causing the expansion of the universe now. Rather, it’s “momentum” left over from the inflationary period and the big bang. The same way that when you push a ball it keeps going a while, the universe will keep expanding for a while after it starts until the pull of normal matter starts to make it collapse.
At least, that’s the theory. Dark energy throws a wrench in the works and makes the universe expand increasingly quickly forever. Unfortunately, we don’t really understand dark energy at all.
People hope that by understanding the interaction between quantum mechanics and gravity, dark energy will be explained. But at the moment, it’s a bit of a mystery.
Thanks!I hope they find it out soon because i am really eager to know.And well, i don’t think anymore that the pressure thing i proposed on the other page is actually quite true!Well, that was just a try.Please do post the reason for the expansion of the universe as soon as you know for sure.I know that i might have to wait for really long for it.Thanks again for answering to so many of my questions!
I’m very eager to know the reaoson for the expansion of the universe too! And I and a lot of other people are working on a solution. 🙂 But be warned, people have been trying to combine general relativity and quantum mechanics for about 50 years.
I’m happy to answer questions! That’s why I write this blog! 🙂
If you guys don’t find it out till i grow up, i will join in too!;) By the way, why do atoms spin in their orbits?And if you answer to biology questions too then:
In the primeval period, the formation of life began as the self replicating molecules formed (that is before the micro spheres). How did they replicate?
I’m sorry-i meant why do ELECTRONS spin in their orbits.Silly mistake!
I look forward to when you can join us! I don’t know where you are in school at the moment, but it’s great that you’re asking these deep questions! Curiosity about the world is the mark of a good scientist!
I’m sorry, I can’t answer the question about biology. I really don’t know the answer to it at all. One person to ask might be Dr. Carin Bondair, who’s a biology Ph.D. with an online presence: https://www.facebook.com/pages/Dr-Carin-Bondar-Biologist-With-a-Twist/193162710726173
I don’t know her personally, so I can’t promise anything.
As for why electrons spin in their orbits… there are two possible meanings to that question.
If you mean why do electrons orbit around the nucleus of an atom, they actually don’t! The story is more complicated. Electrons are waves, so they sit around the atom as a spherical wave so that the wiggles at the start of the circle match up with the wiggles at the end of the circle. (I’m glossing over a LOT here. Actually they’re spherical waves, for instance. But this gets the flavor across.)
I wrote an article about this: http://www.thephysicsmill.com/2012/12/24/unreal-truths-the-bohr-model-of-the-atom/
If you mean why do electrons have a property called “spin,” which corresponds to them spinning about their own axis the way the earth spins to make night and day, that’s a different story.
As far as we know, “spin” is just an intrinsic property of many fundamental particles, the same way charge and mass are. But it has important consequences, like matter not falling in on itself!
You see, spin is quantized just like energy and momentum (see this article: http://www.thephysicsmill.com/2012/12/09/the-charming-doubleness-particle-wave-duality/). It comes in half integer increments: …,-1, -1/2, 0, 1/2, 1, …
A powerful result called the spin-statistics theorem tells us that spin 1/2 particles like electrons are “fermions” and they obey the Pauli exclusion principle, which forbids them from overlapping with each other in space. This is why things are solid. I wrote an article about this too:
http://www.thephysicsmill.com/2013/01/27/binary-unity-the-pauli-exclusion-principle/
Does this help?
Dr Carin Bondar has posted that some guy has found all the English alphabets on the wings of butterflies!Pretty cool, isn’t it?!By the way, what you wrote, cleared a serious misconception of mine-so thanks!As of now, i’ve got no questions.I’ll ask as soon as i have one, though.(that doesn’t take too long!)Maybe, in a few hours…
🙂
Astronomers just confirmed the existence of”Dark Energy”, a mysterious repulsive force that acts in opposite to gravity. As the distance increases, the attractive gravitational force decreases but this mysterious repulsive force increases. This repulsive force is pushing galaxies apart; the greater the distance the greater the repulsion. Scientists today do not know what this “Dark Energy” is, but they know that it is causing the entire universe to expand at an increasing rate.
[Quran 51.47]And the heaven, We built it with craftsmanship and We are still expanding.
How could an illiterate man who lived 1400 years have known about the expansion of the universe?
Do you remember how a rose opens up? That is, theouter petals move outwards more than the inner petals? Imagine that those petals have galaxies on them and that we are atthe center of the rose. Now imagine this rose opening up; the farther out the petals are the faster their recession away from the center (where we are). Well this is exactly how the universe expands around us; the farther out galaxies are from us the faster their recession away from us.
[Quran 55.37]If the heaven ripped and itwere a rose like paint…
Here God assures skeptics about Paradise: if the heaven ripped open like a rose then Paradise will as surely contain so and so… Today we know for sure that the universe is expanding around uslikea rose.Do you remember how an ambulance siren sounds like when it approaches you? And how it sounds like when it recedes from you? The soundpitch changes, right? Similarly when a light source approaches you or recedes from you its color changes. If it is approaching you the color shifts towards the blue, and if it is receding from you its color shifts towards the red; the faster it recedes the redder it appears. Today we know that galaxies are rushing away from us from redshifting of their light. The more distant galaxies are the more reddish their colors appear to us. When you apply paint the colors’ intensity is not even but rather it changes with distance:Similarly the more distant galaxies are the more reddish their colors appear to us, that is, there redness is a function of distance. This is becausethe farther galaxies are the faster they are receding from us (like a rose). The Quran describes it as: “Rose like paint”, that is, it’s color varies with distance.
Hey!
Today’s question :
Why does total internal reflection occur?
I know that it occurs when a ray of light traveling through a relatively denser medium strikes the denser-rarer medium interface at an angle of incidence greater than the critical angle.I also know that the critical angle for a pair of media is the angle of incidence of the ray from the denser medium corresponding to which the angle of refraction would be 90 degrees.What i want to know is that-why is the ray totally reflected back into the relatively denser medium?
Well, I’ve got two more questions today!
1. We know that chlorophyll looks green because the pigment absorbs red and blue, but reflects green which meets our eye.But then, why do the other things look to be of their particular colors?I mean the reason can’t be the same, can it?Chlorophyll absorbs red and blue because it needs the two for the growth of the plant.But why would other things absorb and reflect certain colors if they don’t (probably) need any?Why do they look to be of their certain colors?
2. How do cameras work?How do they record and save images?
Sorry for the delay. You’ll notice I’m a lot slower to respond over the week than over the weekend that’s normal I’m afraid.
I’m glad I was able to clear up a misconception!
Okay, so in order:
Total internal reflection is actually just the extreme result of refraction. When light passes from a high index of refraction material to a low index of refraction material, it gets bent, right? Total internal refraction is when the bending is so extreme that the light just comes right back into the high index of refraction material.
That’s one way to think about it, anyway. The other way to think about it is that when a wave changes speed at the interface, some bit of the wave is always transmitted and some bit is always reflected. And the proportion depends on the angle. Greater than the critical angle, all of the wave will be reflected.
This is actually a general property of waves, not just light waves. If you’re not careful to match the resitances in two wires that you connect in an electrical circuit, you can accidentally reflect the signal you were trying to send back to where it started. The art of making sure the wires match is called impedance matching: https://en.wikipedia.org/wiki/Impedance_matching
1. This is a really excellent question. It’s also the exact same question I asked my high school chemistry teacher. The answer is… surprisingly complicated. Color can come from a lot of different places. Let’s talk about the simplest answer: why different elements–pure ones like hydrogen and helium–are specific colors.
This comes from the allowed energies of electrons within the atom. Remember how I told you that electrons are waves, that fit around the atom? And that they need a certain integer number of wavelengths–I like to call them wiggles–to fit? (The article I posted a link to will help. It has some nice pictures: http://www.thephysicsmill.com/2012/12/24/unreal-truths-the-bohr-model-of-the-atom/) Well the energy the electron has at a given time has to do with the number of wiggles it has. And the number of wiggles it has has to do with the distance it is away from the nucleus of the atom.
When a photon (a light particle. Remember light is both a particle and a wave. See: http://www.thephysicsmill.com/2012/12/09/the-charming-doubleness-particle-wave-duality/) hits the atom, it carries some energy that depends on the color of the light. If the electron takes that energy and absorb the photon, it will have some new number of wiggles. And if that number of wiggles doesn’t fit around the nucleus at some radius, then the electron isn’t allowed to absorb the photon.
If the new number of wiggles does fit, the electron absorbs the photon and the atom can absorb that color of light.
So the quantum mechanical properties of electrons around an atom control what colors of light the atom can absorb and what color the atom appears!
Chlorophyll is similar, but much more complicated. Plants have simply evolved to have chlorophyl in them so that they can absorb blue and red light.
2. Let me answer your question about cameras in a full blog post, because it’s a very good question, but the answer is pretty in depth.
For now, I’ll just say that digital cameras have a grid of tiny boxes. Each box contains a special metal called a semiconductor which absorbs light. When it absorbs light, the semiconductor produces an electric charge, which travels to through a circuit and tells a computer chip that that cell lit up. Then we can save the image.
I know a lot less about film cameras. The film is made of a special chemical that changes color when exposed to light. So if you expose it to the light of day for a brief second, the bright light will make a shape on the film.
Does this help?
I talk a little bit about why LASERS are a single color in my newest post about lasers. You might like it. It also has some information on how physicists think of materials absorbing and emitting light:
http://www.thephysicsmill.com/2013/11/17/things-work-lasers/
Hey!I like the article on lasers and i am eagerly waiting for your post on digi-cams!And as usual, your info has helped quite a lot.
By the way, I wasn’t able to concentrate on anything at school because i had a question to be answered.Here it is-“if it hits the new medium at an angle, some light hits the interface first and changes speed before the rest of the light. And if one side of the beam of light is travelling at a different speed than the other side, the LIGHT WILL BEND.”Why?I tried to visualize it happening, but i still don’t see the reason.Can you help?
1.When did time begin?
2.What exactly is a flame?I mean what is that bright, mostly yellow-orange thing made up of?And is it a gas, a solid or a liquid?
Sorry!I don’t think its a solid or a liquid-all i wanted to ask is that in what form is it?!
No problem. In order:
0. I can give you an analogy for why light bends, and a totally different way of thinking about it. And hopefully one of them will feel right. Often one explanation in math or physics makes sense for one person but not another. And the second person needs a different explanation.
I like to imagine the light beam as a plant stem… a rigid one. So if one side of hte stem is growing faster than the other, the slower-growing side is pulling back as the faster growing one is pushing forward, and the stem bends. If you imagine the beam of light as the plant stem, this helps understand refraction.
Another completely different way to think about it is to use the “principle of least action.” I decribe this in both my article on refraction (here: http://www.thephysicsmill.com/2013/02/17/refraction-how-we-see-through-the-looking-glass/) and my artilcle on Feynman path integrals (here: http://www.thephysicsmill.com/2013/07/16/reality-is-the-feynman-path-integral/). In this way of thinking, we completely restate the question. Before, we assumed that the light starts somewhere, going some direction. And we asked where it goes. Now, let’s assume we know where the light beam starts, and where it ends up. And we ask, how does it get to its final destination? The answer is that the light will take the path that gets it to its final destination in the least amount of time. This is called the “principle of least action.” Here’s the wikipedia article: https://en.wikipedia.org/wiki/Principle_of_least_action.
Now, if the light passes between two materials where it’s speed is different on its way to its final destination, it will bend. It will choose to spend some time in the high-speed medium and some time in the low speed medium in such a way that it gets where its going as fast as possible. (Remember, high index of refraction means light goes slower in that material.)
Of course, this is wildly unintuitive. It almost endows the light with sentience… and the notion of time is different, because we’re imagining we know what happens in the past and the future, but not in between. However, the principle of least action is a very powerful tool… it can be combined with a mathematical technique called “calculus of variations” to derive the standard equations of physics very easily.
1. Assuming that we had a big bang, time began at the big bang. If we did not have a big bang, it’s possible that time never began. One model of inflation, called “eternal inflation” (link to wikipedia: https://en.wikipedia.org/wiki/Eternal_inflation) says that the universe has always existed in an inflationary state where space is always expanding everywhere at an exponential rate. But, once and a while, the inflaton which causes inflation disappears in a small area… just due to quantum fluctuations, and gives its energy to “normal matter.” This creates a stable “bubble” where stars and planets can form. Our universe could be one such bubble. In theory, if this is true, we might be able to see evidence of eternal inflation by looking for evidence of collisions of our bubble with other bubbles in the distant past. So far we haven’t seen anything, but the theory hasn’t been disproven. It’s popular among string theorists.
2. A flame isn’t actually a material at all. What we perceive as “fire” is the heat given off by the chemical reaction of oxygen with other materials. You see, oxygen is highly reactive, and it likes to bond with other atoms. When it does, it releases a lot of energy in the form of heat, which we perceive as fire. This is why fire needs oxygen.
(Heat, by the way, is actually just random motion. Atoms and molecules are alway moving or jiggling around very fast. And the faster they are, the hotter we perceive a material to be. This is because when they hit us, they’re giving us some of the energy from their motion.)
The reason atoms like to bond and form molecules is based on quantum mechanics, by the way. I wrote an article about that too:
http://www.thephysicsmill.com/2013/11/02/a-moving-sea-covalent-bonding/
Thank you so much!The plant-stem explanation is the best one for me.Today’s questions:
1. What is a wormhole exactly?
2. Can you tell me about the Bermuda Triangle mystery?
I’m glad I could help! Be careful with the stem analogy. It is just an analogy.
1. Put simply, a wormhole is a “shortcut” in space and time. Imagine you’re in New York, and you’d like to go to Beijing. You could take the long way around walk (or fly) over the surface of the Earth. But wouldn’t it be nice if you could dig a tunnel straight through the planet? A wormhole is very much like that. But it’s not a tunnel through a planet, it’s a tunnel through the very fabric of spacetime. General relativity tells us space and time are not separate. They’re two parts of the same fabric. In this picture, every moment in time doesn’t appear and vanish, it just exists, eternally, waiting for you to happen upon it as you travel forward in time. This means a wormhole is one means of time travel, because you could travel through one to your own past.
One way that wormholes are formed by a black hole and a white hole pair. You see, the mathematics of general relativity tell us that a black hole is paired with a “white hole,” which is a point in space time out of which all matter emerges but into which none may enter. The idea would then be that stuff enters the black hole and leaves the white hole. We’ve never observed a white hole, however, and they’re generally believed to not exist. The reason is that the equations also tell us that the white hole part of the solution is highly unstable and collapses when matter passes through it, unless we stabilize it with negative energy… which doesn’t exist.
You can form wormholes other ways, but they all involve negative energy.
I wrote an article on using general relativity to travel faster than light. it has some information on wormholes: http://www.thephysicsmill.com/2012/12/02/ftl-part-3-general-relativity-shortcuts/
2. The idea of the bermuda triangle mystery is that ships and planes mysteriously disappeared there, right? I don’t know the definitive answer to this (and there probably isn’t one). But my understanding is that the Bermuda triangle is not special in this regard. Ships and planes have disappeared a lot over the centuries… usually in storms. And they usually just sank, no mystery at all. And in the case of the Bermuda triangle, people have neglected to mention the storms. Over time the storms are forgotten and the disappearance becomes a mystery. It’s like a scary story. The story gets better and better with every retelling, but the reality is mundane. So I think the Bermuda triangle is just mundane.
But, you should draw your own conclusions about it, since I don’t think anyone really knows the answer and I don’t know much about it.
Here’s some places to start: http://en.wikipedia.org/wiki/The_Bermuda_Triangle#Kusche.27s_explanation
http://www.howstuffworks.com/bermuda-triangle.htm
Thanks a million for all the answers Jonah!I can’t wait to join you all!For now,no new questions.Doutlessly, i will come back when i have them.As always, i don’t think it would take too long.Thanks again!
B)
Happy to help. I’m just happy to see someone excited about physics!
Hi!
Today’s questions:
1.What is a zero-point-field?
2.What is the string theory?
Hi!
1. Zero point energy is the energy of empty space. It’s hard to explain why this exists, but I will try. It involves some very weird consequences of quantum mechanics.
Remember how electrons in the atom are waves, whose wiggles determine their energy, and they only fit certain distances away from the nucleus? One weird consequence of this is that the minimum energy of an electron in an atom is not zero. There’s some minimum distance from the nucleus and some minimum number of wiggles the electron can have… and the electron has this much energy. (This is less energy than outside the atom, actually, because the electron is attracted to the proton). But something very similar happens everywhere. The “minimum amount of energy” a particle can have is not zero.
Now here’s the weirdest part. Because of the Heisenburgh uncertainty principle, we can’t know both the energy of a particle and the duration of its existence precisely. (I explain the uncertainty principle on a surface level here: http://www.thephysicsmill.com/2013/01/13/resolution-fourier-analysis-and-the-heisenberg-uncertainty-principle/) This means that, if we look at a patch empty space for, say, one one trillionth of a second, we don’t know the energy contained in that patch very well, and particles—which are essentially little packets of energy, and which have a minimum energy—can appear during that time, so long as they’re gone before the one trillionth of a second passes. The minimum energy of the particles popping in and out of space gives us a minimum energy for empty space itself. This is the zero point energy.
By the way, the existence of particles in empty space has been experimentally verified by observing something called the “casimir force.” The idea is that if we bring two metal plates close enough together, they can prevent particles from forming between them. The reason is that the particles are waves, and they have a wavelength, just like the electron in the atom, and the shorter the wavelength (or the more wiggles), the higher the energy. If we you bring the plates so close together that the only wavelength the particles between them could have corresponds to too high an energy, particles will stop appearing. Then, the particles around the two plates, which are still appearing and disappearing, will push on the plates. Usually you don’t feel this push because there are particles pushing on you from all sides. Not so for the plates, because no particles are between them. And so the plates are pushed together. Here’s the wikipedia article: https://en.wikipedia.org/wiki/Casimir_force
There is something seriously wrong with our understanding of zero point energy, however. Theoretically, zero point energy could be the cause of dark energy. But if you feed our predictions for zero point energy into the equations for general relativity, you find that we should have 10^120 times more dark energy than we actually have. For comparison, there are 10^82 atoms in the universe. And 10^82 is to 10^120 as the mass of a cat is to the mass of the Earth. This is considered the worst prediction in the history of physics.
2. String theory is an approach to unifying gravity and quantum mechanics by finding a “theory of everything” that describes all the forces of nature together. It does it with a really beautiful idea. We know that we can treat gravity not as a force, but just as the shape of space and time. String theory asks if we can do the same thing with the other forces so that, at the end of the day, all we are is geometry. To do this, you have to add more dimensions to space and time, one new dimension for every force. This would mean we live in a 7-dimensional space, minimum. For technical reasons, most theories have 11. And you also have to explain why we don’t perceive ourselves as living in 7 dimensions, but only as living in 4. (Or 3 spatial dimensions.) The argument is that the dimensions are very small, and curled up.
I wrote about an early predecessor to string theory called Kaluza-Klein theory, which only unifies gravity and electromagnetism, and only has 5 dimensions. It’s a nice “toy model” for how string theory works, so I recommend you read that post: http://www.thephysicsmill.com/2013/04/28/stuff-from-shape-kaluza-klein-theory/
By the way, string theory isn’t the only approach to unifying quantum mechanics and general relativity. I work on another approach, called “Causal Dynamical Triangulations,” which I wrote about here:
http://www.thephysicsmill.com/2013/10/13/causal-dynamical-triangulations/
Thank you!
By the way, how are positive and negative electric charges different from each other?
Happy to help. 🙂
This is a hard question. You’re probably aware that like charges repel. So two positive charges repel each other. And two negative charges repel each other. But opposite charges attract, so that a positive charge and a negative charge attract. If we were to describe at a surface level how positive and negative charges are different, that would be it.
We can, of course, go a bit deeper. Negative charge is carried by a number of elementary particles. Elementary particles are the stuff everything else is made of. They’re called elementary because, at the moment, we don’t think we can break them up into smaller things. So we say a bigger object carries electric charge because its constituent elementary particles carry charge.
Here’s the wikipedia article on elementary particles: https://en.wikipedia.org/wiki/Elementary_particle
There are even other “types” of charge that behave like electric charge. We now know that some of the elementary particles carry “color charge,” which is like electric charge, but comes in three “colors.” So there aren’t positive and negative color charges, there are red color charges, blue color charges, and green color charges. And the interactions between them are more complicated. The attraction and repulsion between color charges is called the “strong force,” and it’s very short-range: it’s only visible within atomic nuclei.
Here’s the wikipedia article on color charge: https://en.wikipedia.org/wiki/Color_charge
But, we don’t know WHY the elementary particles have charge, electric or color. And we don’t know why there are different types of charge. This seems to be a fundamental property of the universe. And asking why there’s charge is like asking why there’s stuff at all. It’s a good question, but we don’t know the answer… and we very well may never know.
That’s not to say people haven’t tried. In some versions of string theory, charge emerges as a property of the shape of the tiny curled up dimensions. If you were a subatomic particle and small enough that you had room to move in the dimension (the idea is that us big things completely fill up these dimensions, so we don’t notice them because we can’t move in those directions), then if you walked in the direction of the small curled up dimension long enough, you’d end up back where you started. They loop back on themselves. And the number of times the shape of the three-dimensional universe (plus time) repeats itself (and it must repeat itself at least once) while you walk determines the charge. Of course, we don’t know if string theory is correct. It’s only one of many competing theories to explain quantum gravity.
Hello!!!
Thanks for the reply 🙂
Today’s question:
1.Can you tell me about ‘secondary flow’ and its relation with swirling of water as it gets drained through a hole?
2.How is the universe supposed to be according to the theory of general relativity?
3.What exactly is a dimension?
Hi! Sorry for the late reply. This week has been pretty hectic for me.
1. I have to admit that you’ve reached the end of my knowledge with your first question. I know very little about fluid dynamics. Unfortunately, physicists tend to get very specialized, and fluids is one topic I haven’t really studied.
I can tell you roughly what “secondary flow” is, though. “Secondary flow” is the name we give to fluid when it behaves in a way that the simple mathematics we tried to use doesn’t completely capture the behavior of the fluid.
Let me explain. You see, fluid dynamics is incredibly complicated and difficult. To capture the behavior of most real fluids, we need to use computer simulations to study the fluid we’re interested in. This is very different from most types of physics, where at least some progress can be made with a pencil and paper.
If we make enough approximations, we can make some predictions about fluids… and this gives notions like “Bernoulli’s principle” (see https://en.wikipedia.org/wiki/Bernoulli%27s_principle) and “streamline flow.” (see: https://en.wikipedia.org/wiki/Laminar_flow).
However, these notions don’t capture everything about a fluid. So there’s other stuff in the fluid going on, like vortices and whirlpools. To capture that, you really need a computer simulation. If you’re lucky, though, your approximation works for the most part, and you only need little corrections. The little corrections are the “secondary flow.”
As for what this has to do with water going down the drain… I really don’t know if I can give you a better explanation than what’s already out there. HowStuffWorks has a nice article on tornados that talks a little bit about it: http://science.howstuffworks.com/nature/climate-weather/storms/tornado.htm
2. Your second question is pretty tough too, because I’m not sure how to interpret it. There are a lot of levels of “how the universe is supposed to be.” General relativity tells us that space and time are really two sides of the same coin. By changing how we move, we can transform space into time, and vice versa. It also tells us what the “shape” of spacetime and the universe should be. Massive objects like the Earth curve space so that the straightest path is towards the planet.
But what about the largest scales. What does general relativity tell us about the shape of the universe as a whole? The answer is… well, we don’t really know. The shape of the universe depends on the distribution of the stuff in it, which depends on the shape of the universe, which depends on… well, you get the idea.
But we can make some guesses to try and see. If we assume that stuff is distributed roughly evenly throughout the universe (this is called “homogeneity”) and that no direction is special (this is called “isotropy”), then we can find the “Friedman-Robertson-Lemaitres-Walker solution.” This tells us that the universe is expanding in time. (If you imagine space and time as two parts of the same thing, then the universe looks sort of like an expanding tube. I wrote an article about the shape of the universe, actually. You can find it here: http://www.thephysicsmill.com/2013/03/17/for-there-we-are-captured-the-geometry-of-spacetime/
But there’s a question of the SHAPE of the spatial piece of the universe. It could be the three-dimensional analog of a sphere.(which is not a ball, by the way. A ball has a boundary at the sphere that it fills in. A three-dimensional sphere has no boundary at all. If you walk forever, you eventually return to where you started.) Or it could be a flat box, extending forever in every direction. Or it could be “crumpled up,” like a lettuce leaf. We don’t really know which of these universes we’re in, although it looks like we’re probably either in the sphere (if it’s extremely large… so big we can’t tell it’s curved) or in the flat box. It’s actually a bit of a mystery as to why the universe seems so… flat. This is a mystery that cosmic inflation tries to solve. I wrote three articles on inflation that sort of explain this. Here they are.
The first explains the big bang: http://www.thephysicsmill.com/2013/05/12/always-walk-away-from-an-explosion-the-story-of-the-big-bang/
The second explains why there are problems with the big bang theory: http://www.thephysicsmill.com/2013/06/09/a-mess-of-cosmic-coincidences-problems-with-big-bang/
The third explains how inflation fixes these problems: http://www.thephysicsmill.com/2013/06/26/fixing-the-early-universe-cosmic-inflation/
3. A dimension is essentially the number of non-parallel lines on which you can move. For example, if I’m on a ski lift or a moving walkway, I can essentially only move forwards or backwards… I exist in one dimension. You might think that since there are two directions, backwards AND forwards, there should be two dimensions. But backwards and forwards are on the same line. Most of my life (if I choose not to jump), I can move backwards and forwards, and also left and right. So I live in two dimensions. Left and right are on the same “line” if I draw a line on the floor. Finally, if I get on an airplane, I can move backwards, forwards, left, right, up and down. I can move in 6 directions, so 3 dimensions.
But we could also say that we’re always moving forward in time, so that’s the fourth dimension.
Things get weird when you can only sometimes move in a direction. Say you’re on a spider web. If you’re standing where two strands of web intersect, you can go forwards, backwards, left, and right. So you exist in two dimensions. But if you move a bit to the center of a strand, then you can only go forwards and backwards. You’re suddenly one-dimensional! What happened? Well, a spider web has what we call fractional dimension.
I write more about fractional dimension here: http://www.thephysicsmill.com/2013/01/20/you-cant-get-there-from-here-dimension-and-fractional-dimension/
Hope this helps!
Hello there,
I don’t know if you remember me but I definitely remember you. I used to come to you here to ask you things I didn’t understand or wanted to know about. So I am dropping by to tell you that I’m 17 now and studying science from Pune University (you’ve probably never heard of it before) and my major is going to be physics. I was 13 years old back when I used to come here and ask you things.
It’s weird to read all of that now, and on hindsight – I was such a show off! My attempts at using big words! Sorry I was so full of myself and for my attempts at using the best of my vocabulary and at bookish sentence construction from back then. But talking to you meant to me a lot. It also encouraged me further to study physics on growing up (which is now).
I have a cat, he’s about 1.5 years old. I’m also learning Japanese! And reading a lot.
I hope you have been doing well in everything, in physics but also in other things in your life.
yours,
Pseudonymous
A good day to all,
I was a Radio Officer in the Merchant Navy in my youth. As such I was on board a vessel sailing through the Bermuda Triangle. During my night watch. It was a clear calm night. Static increased across all marine frequencies (from about 400 KHz through to about 25MHz) to such an extent that no signal could be heard through it. I reported this to the Officer of the Watch on the Bridge at the time. If my memory serves me well it lasted for more than 2 hours. We were steaming at about 22 knots. Later I read that underwater disturbances can cause methane gas to rise to the surface and this can cause static. An area of the sea emitting methane gas will not support a ship or for that matter a person… the effects of breathing a high concentration of such a gas I leave to others to explain… I suspect we must have been very close to such an area… I remember being very nervous at the time!
Abdul Latif
I still can’t understand the concept of the senerio of one going 99.5% the speed of light round trip from earth and back in five years then once returned to earth; fifty years have passed. If this is true then time is a variable not a constant.
Well,first of all this not an explanation of time that an eleven year old would certainly understand and I do not agree with your ‘Law of Legos’.In simple words time is the interval between two events and we can only travel forward in time but not backwards because it would mess with the ‘Second Law of Thermodynamics’.
I do not agree with “No matter how fast you go, the light speeds up to stay ahead of you, so that the difference between your speeds is always the same.” If that was true then that means what Einstein said about light is not true,that his theories are false.
Your analogy of legos and the 2nd law as it relates to entropy needs some work.
If every time you go to your collection and remove needed pieces as the numbers dwindle you will be making your collection neater as you approach the last few legos.
Obviously a collection of just two or one lego is neater than a mixed bucket.
In effect there is a bell curve on the entropy.
It gets worse and worse than better and better.
When you reach one, it is a singularity of legos!
Same as capitolism…barring any govt interference (monopoly laws and such) , as in a vacuum of free trade, the end point of capitolism is one single company.
This is probably a dumb question, but i’ll ask anyway. The speed of light is 300,000,000 meters per second. But when you speed up to try to catch it, it goes faster, because light is shy, the light speeds up the same amount that I speed up. So if I find a way to go 1,000,000 meters per second, does that mean the light is now travelling 301,000,000 meters per second?
The following article explains the meaning of time and if you pay careful attention, you might realise why Einstein had no clue what is time.
https://www.linkedin.com/pulse/what-time-john-gabriel