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How would the atomic bomb explosion look like in outer space?  (Source: © aleksandar nakovski /

How would the atomic bomb explosion look like in outer space?

Jaroslav Kores, Ph.D.

In movies, whether we kill aggressive aliens or smash giant asteroids, an explosion in space is always a spectacular affair. What would the explosion of an atomic bomb in a space really look like? 
Whether we eliminate aggressive aliens or giant asteroids in movies, an explosion in space is always a spectacular thing. How would the explosion of an atomic bomb in space vacuum really look like?  I am not an expert on nuclear weapons so I apologize in advance for any inaccuracies. First of all, I would like to point out that "spectacular" explosions in space in movies are rather an example of flaws in physics. Conventional explosives work on the principle of a chemical reaction that requires oxygen. There is enough oxygen on the Earth and there is no need to add it to the bombs but there is no oxygen in space. Therefore, the bombs used on the Earth would be difficult to explode in space - unless an oxygen tank was part of the bomb ...
Is it possible to create two identical snowflakes?  (Source: © Alexey Kljatov /

Is it possible to create two identical snowflakes?

Jaroslav Kores, Ph.D.

There cannot be two identical snowflakes. But what if two flakes were allowed to crystallize in the laboratory, under exactly the same conditions. Would they be the same or not? 
I wouldn't say two identical snowflakes can't exist - it's rather unlikely. There are about 10,000,000,000,000,000,000 ice crystals in a snowflake that randomly coalesce when the snowflake is formed. That's 100,000 times more than the stars in our galaxy or 10 times more than all people´s hair on our planet. We probably know that on different days it is not possible to simply arrange the hair of all people in the same way. So it's similar for snowflakes - finding two identical snowflakes is very unlikely. In reality, the growth of a snowflake is affected by external influences (humidity, air flow, pressure, presence of impurities) and therefore the snowflakes differ from each other ...
How fast is gravity?  (Source: © sdecoret /

How fast is gravity?

Jaroslav Kores, Ph.D.

If the Sun disappeared out of nowhere, would the Earth leave its orbit sooner, later or at the same time that the Sun would disappear from the sky and darkness would come? 
The special theory of relativity shows that it is not possible for any information to spread faster than the speed of light. Thus, the Earth would "learn" of the disappearance of the Sun at the same time that the light from the Sun would stop to fall on it. The speed of gravity spread is the same as the speed of light. The improved theory of relativity (general theory of relativity) deals with the principle of gravity, which describes gravity as a deformation of space-time. When we place a body in the middle of a trampoline, the rubber in the trampoline will deform under its influence. But it does not happen immediately, only in (a very short) time ...
Why does the pond freeze from the surface? (Source: © Wirestock /

Why does the pond freeze from the surface?

Jaroslav Kores, Ph.D.

The warm water rises up, so it should be warmer on the surface of the pond than at the bottom. How is it then possible that a pond always freezes from the surface and not from the bottom? 
Yes, that's right - warmer water rises (that's why there is, for example, a heating spiral at the bottom of a kettle). In addition, this phenomenon works with all fluids (i.e. liquids and gases). This is due to the fact that with increasing temperature, the density decreases and due to gravity, the denser fluid falls and the thinner rises (in the state of weightlessness this phenomenon would not take place).  But water, unlike other fluids, has a peculiarity - in the range of 0-4°C, it behaves the other way round - that is, as its temperature decreases, its density decreases. We call this peculiarity (originally) the water anomaly. In the temperature range 0-100°C (i.e. in the liquid state) water has the highest density at 4°C (exactly at 3.98°C) ...
Andriy BlokhinAndriy Blokhin (Source: ©Andriy Blokhin/

How can a tall spruce pull water from the roots to the top; does it have a pump inside?

Jaroslav Kores, Ph.D.

A tall giraffe pumps blood into its head by its heart. But what draws water to the top of tens of meters high spruce? Trees have no hearts or pumps... 
Capillary elevation is responsible for the nutrition of trees (and other plants) ...  You may think that you will not encounter this phenomenon anywhere else but (like all physics) this phenomenon has a wide use. You could ask in the same way why a cloth or a sponge absorbs water.  Liquid molecules (e.g. water) act on each other by magnetic forces - that's why they also hold the liquid together in a container. These forces are quite large but not as large as in its solid state. Therefore, compared to its solid state, liquid molecules may move a little bit. As a result, liquids do not have a permanent shape - they always take up the shape according to the container ...
Could bacteria fly?  (Source: © Giovanni Cancemi /

Could bacteria fly?

Jaroslav Kores, Ph.D.

To move in a water environment, bacteria have various cilia and flagella that they move forward with but in the air, they are passive travellers depending on where the wind blows them. What actually prevents the bacterium from developing some miniature wings and starting to fly on its own? (Not that we need such a bacterium) 
I am not a naturalist, so I would rather only physically speculate on this issue. I think it's simple — they don’t need to. Evolutionary theory (in my interpretation) shows that the evolution of animal species prefers those “modifications” of organisms that lead to their better development and survival. From a physical point of view, it is much easier to bounce from a substance that has a density of 1,000 kg/m3 than on a substance that has a density of 1 kg/m3. Very simply, we need 1,000 times bigger surface area to bounce in air than in water. This, of course, leads to an increase in the weight of the whole organism and therefore its size ...
Can I walk through the wall thanks to the quantum theory? (Source: © Photobank /

Can I walk through the wall thanks to the quantum theory?

Jaroslav Kores, Ph.D.

According to the quantum theory, the position and velocity of any particle is uncertain, so it may happen that the particle just finds itself somewhere other than where it was. Could it be that all the particles in my body “decide” to be on the other side of the wall and I go through the wall then?
It’s not that simple — more precisely, the degree of inaccuracy in determining the position and together with speed (momentum) is equal to a very small number (Planck’s constant). If the value of the Planck constant was in the order of hundreds of J.s, then we would take going through a wall almost for granted, but because the value of the Planck constant is 1E-34 (very very small), the “strange” behavior of particles (going through a wall, appearing in unexpected places) is limited only by the microworld — that is, electrons. The whole microworld is controlled by probability, and even in the world of electrons, it is not usual for an electron to “go” through a wall but the probability that this will happen is not negligible ...
Can I make diamonds from coal at home? (Source: © Mark Johnson /

Can I make diamonds from coal at home?

Jaroslav Kores, Ph.D.

Both coal and diamonds are made of carbon, only differently arranged each time. Is there a way in which coal could be turned into a diamond? Can diamonds be “cooked” on a cooker at home?
It is fascinating that the same element (carbon) has diametrically different properties only because of the different composition of the crystal lattice. But because there are the same atoms in coal, a pencil lead or a diamond, people wondered after the discovery of the structure of these substances (late 18th century) if a diamond could not be made artificially. Diamonds are thought to be formed at high temperatures (around 1,000 °C) and pressures (billions of Pascals, 10,000 times more than atmospheric pressure). Therefore, if we had pure carbon where we compress each atom, it should not be a problem to produce a diamond which H. Moissan managed to do at the end of the 19th century. It is complicated to achieve such high pressure and especially high carbon purity ...
Why don't airplanes flap their wings? (Source: © vexworldwide /

Why don’t airplanes flap their wings?

Jaroslav Kores, Ph.D.

Planes were inspired by birds and all birds flap their wings when they fly. So why don’t planes flap their wings and they are fixed?
I have rather brief information about the history of flying but I think that the inspiration was based on the free flying of birds when they do not flap their wings (e.g. still used today by gliders). The principle of gliding (and therefore the flight of an aircraft) is different from flapping wings. When flapping its wings, a bird rises due to the fact that it bounces off the air. This requires a large wing area and at the same time the small weight of the bird. The force that we exert on the air is from Newton’s 3rd law that it is the same as the force that air exerts on us. But the air is fluid and very well compressible. So the wings compress the air and the force that the air will exert on the wings is smaller than if we were flapping like that in water ...
Where does all the light go when I turn the lights off? (Source: © TOimages /

Where does all the light go when I turn the lights off?

Jaroslav Kores, Ph.D.

When I close myself into a room without windows and turn the light on, where does all that light go when I turn it off again? We could ask a similar question with sound (where does sound disappear when I turn off its source) or with waves in a swimming pool. And I will try to explain all of these issues.
Like sound or waves in water, light is a wave, only in the case of light, it is an electromagnetic wave while sound is a mechanical wave. So if I describe the waves on the water surface, we can imagine the behavior of light in the same way. Instead of a room without windows, we will describe an arbitrarily large swimming pool with water. If we throw a stone into a pool, we will see the waves propagate from the point of impact. Their height determines how intense the waves are (or how loud the sound is or how much light shines). The waves will propagate through the swimming pool and we will see how their height decreases when they touch the edge of the swimming pool the waves will bounce and propagate back. When they bounce, their height decreases again ...
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