Large galaxy clusters, equivalent to on this Hubble Area Telescope picture, will help astronomers take a look at theories about dark matter and darkish power. Credit score: ESA/Hubble & NASA, RELICS
Our universe is shrouded in thriller, with about 70 % of it consisting of darkish power. The precise nature of darkish power stays a puzzle that, as soon as solved, may unlock profound insights into the formation of our solar system, the evolution of the Milky Way Galaxy, the origins of life, and even the destiny of our universe.
Darkish power might be described because the impact of a detrimental stress pushing space outward. We’ll get extra technical, I promise, however let’s begin with an analogy to know this basic idea. Think about you could have a balloon representing the whole universe, and also you place stickers throughout its floor to symbolize galaxies or clusters of galaxies. Think about the primary pump of air into the balloon — this equates to the Massive Bang and initiates the start of time as we all know it. Because the balloon expands and time passes, the space between any two stickers (or galaxies) will increase. That is just like how galaxies are transferring farther aside from one another, displaying proof for an increasing universe.
Not solely is the universe increasing, however it’s increasing at an accelerated charge, which means it’s getting larger sooner and sooner over time. In our balloon analogy, think about blowing air into the balloon quickly, making it develop sooner and sooner. This extra stress represents darkish power pushing the balloon (or our universe) to develop at an accelerated charge.
Darkish power and dark matter
Earlier than diving deeper into the depths of darkish power, you may be asking what the distinction between darkish power and dark matter is, or how they may be comparable. Darkish power and dark matter, the enigmatic duo, make up about 96 % of the universe (roughly 70 % darkish power and 26 % dark matter). In the meantime, baryonic, or regular, matter, equivalent to stars, crops, cats, you, and me, solely accounts for about 4 % of the universe’s contents.
Associated: Are the percentages of dark matter and dark energy stable?
Whereas the phrases are sometimes confused, the results of darkish power and dark matter are very completely different. Darkish power is a theoretical type of power that counteracts gravitational attraction and drives or “pushes” the universe’s accelerated enlargement. However, dark matter exerts a gravitational affect that may be detected by its results, which “pull” collectively stars and galaxies, affecting their motions.
Whereas their results differ, they each earn their mysterious first title, “darkish,” as a result of we can not immediately observe them. Neither emits, absorbs, nor displays mild. But, we can observe how darkish power and dark matter work together with regular matter. This permits astronomers to attain the seemingly unimaginable and research one thing we are able to’t see.
Detecting the unseen
Darkish power’s acceleration results had been first discovered by observing distant supernovae in the late 1990s. This was performed with Sort Ia supernovae, which act as “customary candles,” which means they’ve a predictable luminosity. So, the fainter certainly one of these supernovae seems, the farther away it’s. This makes them beneficial for measuring distances throughout huge cosmic epochs. By observing their brightness and redshift (a proxy for distance, which is affected by the enlargement of the universe), scientists can hint the historical past of cosmic enlargement and infer the affect of darkish power.
It may also be studied by analyzing baryon acoustic oscillations (BAOs). BAOs are common fluctuations within the density of seen matter attributable to stress waves within the early universe. Basically, they trigger galaxies to cluster extra strongly at particular scales, which then change throughout completely different epochs because the universe expands. So, BAOs additionally present a “customary ruler” for measuring distances over cosmic scales. Massive surveys do that by creating maps of the universe, permitting astronomers to check the dimensions of BAOs to hint the enlargement historical past of the universe and constrain darkish power parameters.
One other modern method to understanding darkish power includes analyzing the bending of sunshine (gravitational lensing) from distant galaxies and clusters. By analyzing the distortions within the shapes and positions of galaxies attributable to gravitational lensing, scientists can probe the distribution of dark matter and additional infer the properties of darkish power by observing how its affect impacts buildings all through the universe.
Our future is in darkish power’s fingers
Ongoing and future surveys just like the Dark Energy Survey (DES), the Legacy Survey of Space and Time (LSST), the Euclid mission, the Baryon Oscillation Spectroscopic Survey (BOSS), and the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) intention to develop our understanding of darkish power by observing bigger volumes of the universe and refining cosmological measurements.
These multi-million-dollar, decade-long experiments would possibly expose the reply to how darkish power has formed our universe or the way it might but destroy the universe (or doubtlessly reveal one other!).
There are three theories about how darkish power may impression the destiny of the universe. The primary concept is warmth demise or the so-called Massive Freeze. On this state of affairs, darkish power retains pushing galaxies farther aside, inflicting the universe to change into emptier and darker. Ultimately, all the things — together with us if we’re nonetheless round — will attain a uniform temperature. To think about a case just like the Massive Freeze, image putting our balloon within the freezer. Ultimately, with sufficient time, the balloon will attain the identical temperature because the freezer, relinquishing all of the properties we beforehand related to how a balloon features at room temperature. The identical applies to our universe.
The second is a captivating conjecture often called the Massive Rip state of affairs. Based on this speculation, the pervasive affect of darkish power will propel the universe’s enlargement at an more and more fast tempo. In the end, cosmologists theorize that this relentless acceleration will attain some extent the place it exerts a power so potent that it rends aside celestial entities. Equivalently, that is an instance I’m certain all of us have skilled when blowing up a balloon. While you push an excessive amount of air into the balloon too rapidly, the balloon pops and is strewn across the room, forsaking balloon fragments and stickers — or, within the cosmic case, galaxies and planets — that had been blown aside.
The third state of affairs is known as the Massive Crunch, which is the other of enlargement. It means that the results of darkish power may change from inflicting the universe to develop to inflicting it to break down. This might result in all the things collapsing in on itself and probably resetting us again to the way in which issues appeared firstly of time. This might be like letting all of the air out of our balloon and watching the chaotic universe fly across the room till it peacefully rests on the bottom, ready to be blown up once more.
