Why do you remember some dreams well and some are forgotten as soon as you wake up?

Why do you remember some dreams well and some are forgotten as soon as you wake up?

Annukka Isovaara, 5

People usually have numerous dreams during the night, but most of them are dull dreams, and they remain outside of consciousness. If you forget the dream right away, its content is probably meaningless.

Sometimes, however, even a boring dream can deal with some unfinished or meaningful thought that was awake, in which case the dream is remembered for a longer time. The contents of dreams can often seem silly or even nonsensical, but still there may be a connection with the events or thoughts of the previous days.

Sometimes the dream content arouses such strong emotions that the dream awakens. In this case, the dream is usually remembered particularly well. It is due to two reasons. First, the emotional reaction is so strong that it strengthens the memory trace in the brain. In addition, upon waking up, the mind begins to process dream observations, which also helps to remember.

If you want to remember your dreams, you should talk about them and you can write or draw them right after waking up.

Liisa Kuula

PhD in psychology

University of Helsinki

Why is coral an animal?

Sampo Hulmi, 3

Corals and thousands of species of their closely related sea anemones are known. Some of them resemble, for example, branches, flowers and even broccoli to such an extent that in the past people believed they were plants. Corals are also attached to the bottom and may sway in the waves like aquatic plants.

However, some people who studied nature already understood about a thousand years ago that corals must be animals. They probably discovered, for example, that corals retract into their mouths if touched with a finger, and many have a prominent mouth-like structure.

Still, it was only after the invention of the microscope, i.e. hundreds of years later, that people became convinced that corals are indeed animals. This probably happened around the middle of the 18th century.

Corals have been found to have a stomach-like pouch-like interior, stinging predatory tentacles, muscle and nerve cells, and other animal-like structures, though no brains or blood vessels, for example. Sea anemones even have a leg-like part that allows them to move slowly!

However, many corals have a surprising connection with plants. Namely, they grow huge amounts of tiny algae inside their cells, i.e. their kind of building blocks.

It is a mutually beneficial coexistence that enables coral reefs to exist. However, it means that many corals have to live right near the surface of the water to get enough sunlight for these internal plants.

Markus Dernjatin

marine and environmental biologist

Why does ice float on the surface of water?

Alva Härmänmaa, 4

When on a summer’s day, we enjoy a cold drink with ice cubes floating on the surface or we admire the surface of a frozen body of water in the winter, we don’t necessarily think that behind the phenomenon there is a quite subtle and interesting interaction.

In order for an object to float in a liquid at all, the density of that object must be lower than the liquid. So, expressed in everyday language, that object must be lighter than the same amount of liquid. That’s why, for example, a block of wood or a toy boat floats on the surface of the water.

When the two states of the same substance, liquid and solid, are at rest with each other, the solid is usually denser and therefore does not float on the surface of the liquid but sinks to the bottom. It is due to the fact that when a substance freezes solid, the smallest structural parts of the substance, i.e. the atoms or the molecules they form, usually pack closer to each other in a regular structure.

However, water makes an exception to this.

Namely, water consists of one oxygen atom and two hydrogen atoms, which together form a v-shaped structure. The part on the oxygen side of that structure is slightly electrically negatively charged, and correspondingly, the part on the hydrogen side is positively charged. This leads to the fact that when the water freezes and the molecules arrange themselves in a regular order, the charge causes the molecules to arrange themselves a little further apart than they would otherwise.

The end result is that ice is less dense than liquid water – and that’s why ice floats on the surface of water.

Tom Kuusela

University researcher in physics

University of Turku

How much is the universe expanding per second?

Niilo Jylhänlehto, 6

The universe the expansion has continued since the big bang, i.e. about 13.8 billion years. Enlargement is only noticed when looking at really distant objects.

As the universe ages, the rate of expansion slowly changes, and the expansion is currently accelerating due to a phenomenon called dark energy. The rate of expansion is also proportional to the distance of the object. That is, the further the object is from us, the faster it moves away from us.

If we look at the limit of the observable universe, i.e. the farthest corners of the universe from which light has reached the Earth since the Big Bang, the distance there increases at the current rate of expansion by no less than 970,000 kilometers in one second. That distance corresponds to the distance of about 23,000 marathons.

The border in question is located approximately 46.5 billion light years away from us.

The distance from us to the edge of the observable universe expands by almost a million kilometers per second! Light travels about a third of that distance per second, so the universe is clearly expanding faster than the speed of light. So the light now leaving the edge of the observable universe will never reach the Earth.

Atte Keitaanranta

astrophysics elective researcher

University of Helsinki

Send the question, the questioner’s full name and age to lasten.tiedeskö[email protected]. The column is provided by Touko Kauppinen.