Scientific Facts

If the Sun were made of bananas, it would be just as hot?

The Sun is hot, as the more astute of you will have noticed. It is hot because its enormous weight – about a billion tons – creates vast gravity, putting its core under colossal pressure. Just as a bicycle pump gets warm when you pump it, the pressure increases the temperature. Enormous pressure leads to enormous temperature.
If, instead of hydrogen, you got a billion billion billion tons of bananas and hung it in space, it would create just as much pressure, and therefore just as high a temperature. So it would make very little difference to the heat whether you made the Sun out of hydrogen, or bananas, or patio furniture.
Edit: this might be a little confusing. The heat caused by the internal pressure would be similar to that of our Sun. However, if it's not made of hydrogen, the fusion reaction that keeps it going wouldn't get under way: so a banana Sun would rapidly cool down from its initial heat rather than burning for billions of years. Thanks to people who pointed this out.

All the matter that makes up the human race could fit in a sugar cube

Atoms are 99.9999999999999 per cent empty space. As Tom Stoppard put it: "Make a fist, and if your fist is as big as the nucleus of an atom, then the atom is as big as St Paul's, and if it happens to be a hydrogen atom, then it has a single electron flitting about like a moth in an empty cathedral, now by the dome, now by the altar."
If you forced all the atoms together, removing the space between them, crushing them down so the all those vast empty cathedrals were compressed into the first-sized nuclei, a single teaspoon or sugar cube of the resulting mass would weigh five billion tons; about ten times the weight of all the humans who are currently alive.
Incidentally, that is exactly what has happened in a neutron star, the super-dense mass left over after a certain kind of supernova.

Events in the future can affect what happened in the past

The weirdness of the quantum world is well documented. The double slit experiment, showing that light behaves as both a wave and a particle, is odd enough – particularly when it is shown that observing it makes it one or the other.
But it gets stranger. According to an experiment proposed by the physicist John Wheeler in 1978 and carried out by researchers in 2007, observing a particle now can change what happened to another one – in the past.
According to the double slit experiment, if you observe which of two slits light passes through, you force it to behave like a particle. If you don’t, and observe where it lands on a screen behind the slits, it behaves like a wave.
But if you wait for it to pass through the slit, and then observe which way it came through, it will retroactively force it to have passed through one or the other. In other words, causality is working backwards: the present is affecting the past.
Of course in the lab this only has an effect over indescribably tiny fractions of a second. But Wheeler suggested that light from distant stars that has bent around a gravitational well in between could be observed in the same way: which could mean that observing something now and changing what happened thousands, or even millions, of years in the past.

Almost all of the Universe is missing

There are probably more than 100 billion galaxies in the cosmos. Each of those galaxies has between 10 million and a trillion stars in it. Our sun, a rather small and feeble star (a “yellow dwarf”, indeed), weighs around a billion billion billion tons, and most are much bigger. There is an awful lot of visible matter in the Universe.
But it only accounts for about two per cent of its mass.
We know there is more, because it has gravity. Despite the huge amount of visible matter, it is nowhere near enough to account for the gravitational pull we can see exerted on other galaxies. The other stuff is called “dark matter”, and there seems to be around six times as much as ordinary matter.
To make matters even more confusing, the rest is something else called “dark energy”, which is needed to explain the apparent expansion of the Universe. Nobody knows what dark matter or dark energy is.

Things can travel faster than light; and light doesn’t always travel very fast

The speed of light in a vacuum is a constant: 300,000km a second. However, light does not always travel through a vacuum. In water, for example, photons travel at around three-quarters that speed.
In nuclear reactors, some particles are forced up to very high speeds, often within a fraction of the speed of light. If they are passing through an insulating medium that slows light down, they can actually travel faster than the light around them.
When this happens, they cause a blue glow, known as “Cherenkov radiation ”, which is (sort of) comparable to a sonic boom but with light. This is why nuclear reactors glow in the dark.
Incidentally, the slowest light has ever been recorded travelling was 17 meters per second – about 38 miles an hour – through rubidium cooled to almost absolute zero, when it forms a strange state of matter called a Bose-Einstein condensate.
Light has also been brought to a complete stop in the same fashion, but since that wasn't moving at all, we didn't feel we could describe that as "the slowest it has been recorded travelling".

There are an infinite number of mes writing this, and an infinite number of yous reading it

According to the current standard model of cosmology, the observable universe – containing all the billions of galaxies and trillions upon trillions of stars mentioned above – is just one of an infinite number of universes existing side-by-side, like soap bubbles in a foam.
Because they are infinite, every possible history must have played out. But more than that, the number of possible histories is finite, because there have been a finite number of events with a finite number of outcomes. The number is huge, but it is finite. So this exact event, where this author writes these words and you read them, must have happened an infinite number of times.
Even more amazingly, we can work out how far away our nearest doppelganger is. It is, to put it mildly, a large distance: 10 to the power of 10 to the power of 28 meters. That number, in case you were wondering, is one followed by 10 billion billion billion zeroes

Black holes aren’t black

They’re very dark, sure, but they aren’t black. They glow, slightly, giving off light across the whole spectrum, including visible light.
This radiation is called “Hawking radiation”, after the former Lucasian Professor of Mathematics at Cambridge University Stephen Hawking, who first proposed its existence. Because they are constantly giving this off, and therefore losing mass, black holes will eventually evaporate altogether if they don’t have another source of mass to sustain them; for example interstellar gas or light.
Smaller black holes are expected to emit radiation faster compared to their mass than larger ones, so if – as some theories predict – the Large Hadron Collider creates minuscule holes through particle collisions, they will evaporate almost immediately. Scientists would then be able to observe their decay through the radiation.

The fundamental description of the universe does not account for a past, present or future

According to the special theory of relativity, there is no such thing as a present, or a future, or a past. Time frames are relative: I have one, you have one, the third planet of Gliese 581 has one. Ours are similar because we are moving at similar speeds.
If we were moving at very different speeds, we would find that one of us aged quicker than the other. Similarly, if one of us was closer than the other to a major gravity well like the Earth, we would age slower than someone who wasn’t.
GPS satellites, of course, are both moving quickly and at significant distances from Earth. So their internal clocks show a different time to the receivers on the ground. A lot of computing power has to go into making your sat-nav work around the theory of special relativity.

A particle here can affect one on the other side of the universe, instantaneously

When an electron meets its antimatter twin, a positron, the two are annihilated in a tiny flash of energy. Two photons fly away from the blast.
Subatomic particles like photons and quarks have a quality known as “spin”. It’s not that they’re really spinning – it’s not clear that would even mean anything at that level – but they behave as if they do. When two are created simultaneously the direction of their spin has to cancel each other out: one doing the opposite of the other.
Due to the unpredictability of quantum behaviour, it is impossible to say in advance which will go “anticlockwise” and the other “clockwise”. More than that, until the spin of one is observed, they are both doing both.
It gets weirder, however. When you do observe one, it will suddenly be going clockwise or anticlockwise. And whichever way it is going, its twin will start spinning the other way, instantly, even if it is on the other side of the universe. This has actually been shown to happen in experiment (albeit on the other side of a laboratory, not a universe).

The faster you move, the heavier you get

If you run really fast, you gain weight. Not permanently, or it would make a mockery of diet and exercise plans, but momentarily, and only a tiny amount.
Light speed is the speed limit of the universe. So if something is travelling close to the speed of light, and you give it a push, it can’t go very much faster. But you’ve given it extra energy, and that energy has to go somewhere.
Where it goes is mass. According to relativity, mass and energy are equivalent. So the more energy you put in, the greater the mass becomes. This is negligible at human speeds – Usain Bolt is not noticeably heavier when running than when still – but once you reach an appreciable fraction of the speed of light, your mass starts to increase rapidly.

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Why is Grass Green?

Every object on the Earth has its own color. Rather than calling it an object on Earth, it would be apt to call it an object under the Sun. The color is naturally imparted to it when white light falls on the object. We all know that white light consists of seven rainbow colors. It is evident from the prism experiment, which everyone might have done in their science lab during school days.

Every object appears in its natural color when it reflects and refracts some part of the white light that is falling on it. Snow is white as the white light falling on it reflects and refracts equally without absorbing any light of particular wavelengths. The sky is blue as it absorbs all the other wavelengths of light except blue, among the seven color wavelengths that constitute white light. The blue light is reflected and refracted, and later reaches our eye. Hence, the sky appears blue.

Similarly, grass appears green as it absorbs all the other wavelengths in the light except green. Grasses reflect and refract green light which reaches our eyes and make us identify grass as green color. The exact molecule that is present in grasses, and in fact in all the green plants, which is responsible for the green color is chlorophyll. It is the green pigment present in the chloroplasts (cell organelle) of all plant cells. Chlorophyll has magnesium ion as one of its chemical components.

Chlorophyll converts the inorganic elements called photons, otherwise called energy packets, into energized chemicals. These chemicals release electrons to get changed, and transfer the energy. This energy is used up in synthesizing the organic sugars which act as food for the plant. This chlorophyll, which is identified as green pigment, is able to absorb red and blue lights, and reflects green light.

Why do Dark Colors Absorb Heat?

Dark colors become hotter in sun light than light colors for a reason that dark colors absorb more light. A blue shirt appears blue when the sunlight falls on it and when the blue light energy gets reflected. The reflection of blue light will impart blue color to the shirt as it reaches our eyes. Light colors will reflect more light. Dark color will absorb more light. The light absorbed by the dark clothes will get converted into heat.
Dark colored clothes appear dark as they reflect very less light. Light colored clothes appear bright as they reflect the light more. The light that is not reflected by the dark colored clothes will be more absorbed into the material. So, people are not suggested to wear black in summer because the clothes will get hotter.
Dark colored objects are found to get heated rapidly in strong light as the objects will absorb much of the radiation in the visible wavelengths. The dark objects will turn this energy into heat. The dark colored objects get heated rapidly and also become cool rapidly. This is because the dark colored objects are known to radiate heat when the light stops falling on them.
The dark colored objects are black in color as they absorb totally the electromagnetic radiation. The object that absorbs the entire radiation will convert that energy into thermal energy. While light colors will reflect the electromagnetic radiation completely that makes them to look white. As the object do not absorb anything from the light, it need not convert the light into thermal energy.
As every object appears in a color which is reflected back from them, dark colored objects in order to appear black should not reflect any light. Hence, they absorb total light and change them into heat energy.

Why is Milk White?

The cow and Ox are the animals that give milk that we consume. They have milk secreting cells in the udder region. The blood that is supplied to these cells is separated with red blood corpuscles and hemoglobin in this region. The RBCs and hemoglobin are those that impart red color to the blood. The blood without the hemoglobin pigment will appear pale yellowish. The milk generating cells remove the pigment cells from the blood, of the milk secreting animals and provide milk to us. This is primarily the reason for milk to appear white rather than in any other color.
Generally, the casein protein content makes the milk to appear as white. The cream present in the milk is also found to be responsible for the milk to appear white. The cream of the milk has high fat content. Less fat content or no fat in the milk makes it appear grey. So, milk having more cream will be more whitish and milk which is grayish will have less cream.
Another reason for milk to appear white is that, some objects do not absorb light but reflect the entire spectrum that falls on them. Milk might be doing that. Blood appears red because it absorbs all the wavelengths of light except red, which it reflects. Hence, blood appears red. Milk will not absorb any wavelength in the light and reflects everything and hence it appears white. The cream and casein in the milk are the components that express this physical phenomenon.
In fact, this physical phenomenon is explained in different manner. White is not said to be resulting due to the phenomenon similar to that happening in the case of appearance of other colors like green, blue and red. Milk has colloidal particles. Some of the liquids exist as colloids which is a state of liquid. Colloidal particles scatter the light easily and do not absorb any light. This scattering of entire white light is the main reason for the milk to appear white.

Why is snow white?

Visible light comprises of different frequencies of light. The different frequencies are visualized by us as different colors. The electrons that exist in the atoms that make up the object have various frequencies of vibration. The electrons vibrate to some extent based on the frequency of energy that falls on it. The particles in the object absorb some amount of energy from the light that falls on it. The absorption depends on the frequency of the light that is absorbed by the object from the light. The absorbed energy will be emitted later as heat. The light frequencies that were not absorbed by the object get reflected back.
In the transparent object, the light frequency that is reemitted by one atom will pass through another atom. If the object is very clear and transparent, the unabsorbed light travels all through the material of the object. In the case of solids which are opaque, most of the unabsorbed light will be sent out of the material of the object. The light will not keep passing throughout the object. So the color of an opaque object will be the collection of those frequencies of light that were not absorbed by the particles.
Now, snow is a form of water that is in frozen state. Snow is clear, pure and translucent. The light passing through the ice will not be in a single and direct way. The ice particles alter the direction of light. This happens due to matching of the distances between the ice atoms with that of the light wavelengths. The light interacts with the ice structure. So the direction in which the light entered the ice is changed later by the ice particles.
The unabsorbed light that got reflected from one ice particle will pass through another ice particle and again gets reflected and the phenomenon continues. In this process all the frequencies of light in visible spectrum will be sent out of the material equally in all the directions. As all the frequencies of light which represent various colors are collectively sent out of ice, it appears white. White is the combination of VIBGYOR colors in the visible spectrum. An individual ice crystal might appear in different color, but the whole ice looks white due to the above reason. Since the snow is a very thin layer of ice, it appears white. But, if the ice is very thick then it appears blue due to scattering