The universe is continually expanding, but there is no such thing as something it expands into.
When making a loaf or batch of muffins, place the dough on a baking sheet. As the dough cooks in the oven, it expands in the pan. Any pieces of chocolate or berries in the dough will move away from each other as the bread or muffin expands.
The expansion of the Universe is, in some ways, similar. But this analogy is flawed in one respect: while the dough expands inside the pan, the Universe has nothing to expand into. It simply expands within itself.
It may be difficult to understand, but the Universe is considered to be everything within the Universe. In the expanding Universe there is no pan. Only pasta. Even if a pan existed, it would be part of the Universe, and therefore the Universe would expand with the pan.
Even for me, a physics and astronomy professor who has been studying the Universe for years, these ideas are difficult to understand. You don’t experience anything like this in your everyday life. It’s like asking which direction is furthest north from the North Pole.
Another way to think about the expansion of the Universe is how other galaxies are moving away from our galaxy, the Milky Way. Scientists know that the Universe is expanding because they can track other galaxies as they move away from ours. They define expansion using the speed at which other galaxies are moving away from us. This definition allows them to imagine expansion without needing something to expand upon.
The expanding Universe
The Universe began with the Big Bang 13.8 billion years ago. The Big Bang describes the origin of the Universe as an extremely dense and hot singularity. This tiny dot suddenly underwent a rapid expansion called inflation, during which everywhere in the Universe suddenly broke apart. But the name Big Bang is misleading. This was not a giant explosion, as the name suggests, but a moment when the Universe expanded rapidly.
Then the Universe condensed and cooled rapidly and began producing matter and light. Eventually, it evolved into what we know today as our Universe.
The idea that our Universe was not static and could expand or contract was first published by physicist Alexander Friedman in 1922. He mathematically confirmed that the Universe is expanding.
Although Friedman demonstrated that the Universe is expanding, at least in some places, it was Edwin Hubble who further analyzed the rate of expansion. Many other scientists have confirmed that other galaxies are moving away from the Milky Way, but in 1929 Hubble published his famous paper in which he confirmed that the entire Universe was expanding and that this rate of expansion was increasing.
This discovery continues to intrigue astrophysicists. What phenomenon allows the Universe to overcome the gravitational force that holds it together and, at the same time, to expand, moving the objects of the Universe away from each other? And on top of all this, its rate of expansion is accelerating over time.
Many scientists use an image called an expansion funnel to describe how the expansion of the Universe has accelerated since the Big Bang. Imagine a deep funnel with a wide rim. The left side of the funnel, the narrow end, represents the beginning of the Universe. When you move to the right, you are moving forward in time. The widening of the cone represents the expansion of the Universe.
The expansion funnel visually shows how the expansion rate of the Universe has increased over time. To the left of the funnel is the Big Bang, and since then the Universe has been expanding at an increasingly rapid rate.
NASA
Scientists have not been able to directly measure where the energy causing this accelerated expansion comes from. They were unable to detect or measure it. Because they cannot see or measure this type of energy directly, they call it dark energy.
According to researchers’ models, dark energy should be the most common form of energy in the Universe, making up about 68% of the Universe’s total energy. The energy contained in everyday matter, which makes up the Earth, the Sun and everything we can see, represents only about 5% of all the energy in the Universe.
Dark matter and dark energy make up most of the Universe.
Green Bank Observatory, CC BY-NC-ND
Outside the expansion funnel
So what’s outside the expansion funnel?
Scientists have no evidence of anything beyond our known Universe. However, some predict that multiple universes could exist. A model that includes multiple universes could correct some of the problems scientists find in current models of our Universe.
A big problem with current physics is that researchers fail to integrate quantum mechanics, which describes how physics works at very small scales, and gravity, which governs large-scale physics.
The rules for how matter behaves on a small scale depend on probability and “quantized,” or fixed, amounts of energy. At this scale, objects can pop in and out of existence. Matter can behave like a wave. The quantum world is very different from how we see the world.
On a large scale, which physicists call classical mechanics, objects behave as we expect them to behave in everyday life. Objects are not quantized and can have continuous amounts of energy. Objects do not come in and out of existence.
The quantum world acts like a light switch, where energy only has the ability to turn it on and off. The world we see and interact with acts like a dimmer switch, allowing for all levels of energy.
But researchers run into problems when they try to study gravity at the quantum level. On small scales, physicists would have to assume that gravity is quantized. But the research conducted by many of them does not support this idea.
An infinitely expanding universe lies beyond the Milky Way.
DECaPS2/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA, M. Zamani and D. de Martin via AP
One way to make these theories work together is the multiverse theory. There are many theories that go beyond our current Universe to explain how gravity and the quantum world work together. Some of the major theories include string theory, brane cosmology, quantum cycle theory, and many others.
Regardless, the Universe will continue to expand, with the distance between the Milky Way and most other galaxies increasing over time.
Nicole Granucci does not consult, work for, own shares in, or receive funding from any company or organization that could benefit from the publication of this article, and has not disclosed any relevant relationships beyond her academic position.
Source: Terra
Rose James is a Gossipify movie and series reviewer known for her in-depth analysis and unique perspective on the latest releases. With a background in film studies, she provides engaging and informative reviews, and keeps readers up to date with industry trends and emerging talents.
