The truth is that the universe is expanding itself but expanding in what?

Everything happens outside what can be observed, we have more questions than answers.

One of the greatest discoveries in the 20th century is that the universe itself is expanding . When Einstein introduced general relativity, he quickly realized that there was a consequence of it that made him unhappy. That the universe is filled with matter in every direction, it will be unstable and unable to resist the gravitational collapse, when all objects attract and are destroyed.

In 1917, a year after general relativity was published, Einstein added a concept called gravitational constant . It is responsible for an invisible external force that is preventing the collapse of the universe.

However, if the cosmological constant does not exist, scientists can still prove that the universe does not collapse in another way. Theory and experimental observations since 1930 show that the universe is expanding itself.

The universe is expanding after the Big Bang and has not stopped.

Back in the 1910s, Vesto Slipher, an American astronomer, found that the "spiral nebula" in the sky had a red shift . This is evidence that they are increasingly moving away from us.

The next decade, another American astronomer, Edwin Hubble, proved that the "spiral nebula" observed by Slipher is a galaxy. He also determined their distance from the Earth.

If you combine these two facts you will realize that galaxies are increasingly leaving us . And there's another interesting trend: the farther the galaxies are, the faster they move.

Explaining this, many factors are considered by scientists. For example, light from distant "tired" galaxies, they lose their energy as they travel through space. Or a big explosion that pushes galaxies away from us long ago.

However, only one hypothesis is confirmed by both the general theory of relativity and all the astronomical observations that human beings have then: The space of the universe itself is expanding.

Hubble's research data shows the distant nebulae.

A confusing conclusion for most people. They will wonder "If it extends itself, what does it expand in and how does it? The universe swells like blowing a ball or it stretches like a rubber band?"

The questions are very reasonable. Experience throughout our lives shows that a hot air balloon inflates in all directions, so does a balloon when we fill it with air. But think about this: Do you really need to blow the air to expand the balloon?

May be no need. For example, in case you use your hand to stretch it. And when there is one more person, 4 hands can pull it open in all directions.There are many, many ways to make something expand.

The universe expanded like a balloon, and the galaxies are like dots on it?

But now imagine, you are no longer giant to see a ball like that anymore. You are so narrow that the ball becomes as big as the universe. And your vision is limited to a half-millimeter radius.

At this time, even if the ball is stretched in any way, when you look at all the areas within a half a millimeter radius, you will also see them moving away from you. Not only that, the farther away the area is, the faster their movement speed is. This is like Edwin Hubble has observed since the beginning of the 20th century, and it has so far happened to the universe.

But if the universe expanded, what caused it? Is the cosmic ball stretched by a giant hand outside? Is there still a space outside the universe and someone has blown air inside to bulge? Is there something attached to the ball itself that makes it voluntarily expand? Or is the initial setting of the ball already open?

Is there something outside the universe that is stretching it?

Unfortunately, the most complete and honest answer now is: We don't know. Worse, the next affirmation is: We cannot know. From our position, only the expanding ball can be observed.

Today's science may assume there are more balls than the ball we live on. Then we can follow exactly how the ball expands over time. We can measure all the properties that affect that process.

Indeed, until the problem lies on the ball, science can do it.

Only, beyond the ball we have no information, to say anything. Our universe is now like a 3-dimensional version of the cake surface. Galaxies are like raisins sprinkled on it.

The universe is like a cake, a galaxy like raisins.

We can measure raisins. It can be assumed that there are many raisins and even more cakes outside of our vision. But that's all we know. We can determine the expansion history of the universe, and even discovered it expanding rapidly. But everything happens outside what can be observed, we have more questions than answers.

Can a 2-dimensional ball collapse in 3-dimensional space, can a 3-dimensional universe expand in 4-dimensional space? Is there a bakery outside where we live and can observe and feel? Is our cake endless, or is it just because we are so small to see something outside it? Or is it hatching in a mold and spilling into the microwave?

Scenarios for the expansion of the universe.

Humans not only don't know about those things. We don't even have any ideas to answer these questions. But it is also an interesting science.Until we know about what's outside the universe, just accept the irrational answers of science.

The universe does not need to expand inside anything. Because it is the greatest and the greatest.The universe itself, extends itself.

Because a man has come up with general relativity, and it makes sense for that. But mankind with intelligence still exists, we have not only one man. If we are lucky in the future, we will have easy-to-understand answers.