The ‘raisin bread’ model of the expanding Universe, where relative distances increase as the space (dough) expands. The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received. The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what’s been known all the way back since the 1920s. (Credit: NASA/WMAP Science Team)

Whenever you have a puzzle, you have every right to expect that any and all correct methods should lead to you to same solution. This applies not only to the puzzles we create for our fellow humans here on Earth, but to even the deepest puzzles that nature itself has…

An event like AT2018cow, now known as either FBOTs or Cow-like events, is thought to be the result of a breakout shock from a cocooned supernova. With five such events now discovered, the hunt is on to uncover precisely what causes them, as well as what makes them so unique. (Credit: Shanghai Astronomical Observatory, China)

Every once in a while, a stellar cataclysm occurs in our Universe, bringing the life of a star to an end. The most common type of cataclysm is a core-collapse supernova, where a massive star’s interior implodes, leading to a runaway fusion reaction and a tremendous explosion, where the energy…

Planet Earth’s motion through space isn’t just defined by our axial rotation or our motion around the Sun, but the Solar System’s motion through the galaxy, the Milky Way’s motion through the Local Group, and the Local Group’s motion through intergalactic space. Only with everything combined, and by comparing to the Big Bang’s leftover glow, can we arrive at a meaningful answer. (Credit: Jim slater307/Wikimedia Commons; background: ESO/S. Brunier)

Planet Earth isn’t at rest, but continuously moves through space.

This image shows the supernova remnant of SN 1987a in six different wavelengths of light. By monitoring the same object across wavelengths and across time, we can gain unparalleled insight into what this object’s history, properties, and evolution are. (Credit: Alak Ray, Nature Astronomy, 2017; ACTA/ALMA/ESO/Hubble/Chandra composite)

Some stars die of natural causes. Others meet a grizzlier fate. As they go through their life cycles, most stars will die on time, right when they’re supposed to, as determined by their initial masses. They’ll burn through their fuel until they can fuse elements no longer, and then…

This image shows a depiction of a solar sail, and in particular of the sail used by the Japanese IKAROS mission. The idea of a thin, light, large-area surface has traditionally been based off of “sailing” on particles and radiation emitted by the Sun. However, a similar concept would leverage a highly reflective surface to reflect directed laser light 180 degrees from the surface, enabling direct propulsion and large, continuous accelerations, with the goal of completing an interstellar journey. (Credit: Andrzej Mirecki/Wikimedia Commons)

For all of human history, embarking upon an interstellar journey has been a seemingly unreachable dream, made practically impossible by the enormous distances separating our Sun from any of our stellar neighbors. Even with the most powerful rocket technology ever developed, it would take tens of thousands of years to…

While many unstable particles, both fundamental and composite, can be produced in particle physics, only protons, neutrons (bound in nuclei) and the electron are stable, along with their antimatter counterparts and the photon. Everything else is short-lived, but if muons can be kept at high enough speeds, they might live long enough to forge a next-generation particle collider out of. (Credit: Contemporary Physics Education Project/CPEP, DOE/NSF/LBNL)

If you want to uncover all the particles that fundamentally exist, your best bet is to smash particles together, under controlled, laboratory conditions, at extremely high energies. Whenever two particles collide, they have to conserve both energy and momentum, as well as other quantum properties that have associated conservation laws…

An illustration of our cosmic history, from the Big Bang until the present, within the context of the expanding Universe. We cannot be certain, despite what many have contended, that the Universe began from a singularity. We can, however, break the illustration you see into the different eras based on properties the Universe had at those particular times. We are already in the Universe’s 6th and final era. (Credit: NASA/WMAP science team)

The Universe is not the same today as it was yesterday. With each moment that goes by, a number of subtle but important changes occur, even if many of them are imperceptible on measurable, human timescales. …

In addition to formation by supernovae and neutron star mergers, it should be possible for black holes to form via direct collapse. Simulations such as the one shown here demonstrate that, under the right conditions, black holes of any mass could form in the very early stages of the Universe. However, there must be something novel at play, or this process will not occur until after the first stars have formed. (Credit: Aaron Smith/TACC/UT-Austin)

Whenever we think about the Universe, it’s fun to imagine what else might be out there beyond the limits of what we’ve discovered so far. But as vast as our imaginations are, we have no choice but to rein them in, as they’re constrained by all that we’ve already seen…

Glittering in the sunlight as it recedes from the view of the final stage of the Ariane 5 rocket that launched it, NASA’s James Webb Space Telescope heads towards its final destination with perhaps the maximum amount of fuel we could have hoped for. (Credit: NASA TV/YouTube)

On Christmas day, 2021, NASA’s James Webb Space Telescope successfully launched into space.

The Earth, moving in its orbit around the Sun and spinning on its axis, appears to make a closed, unchanging, elliptical orbit. If we look to a high-enough precision, however, we’ll find that our planet is actually spiraling away from the Sun, while the rotation period of our planet is slowing down over time. The same calendar that we use today won’t apply to the distant past or future. (Credit: Larry McNish/RASC Calgary)

With every year that passes, we assume that two separate things will both line up. One is the seasonal year on Earth: the progression from winter to spring to summer to fall and back around again, coinciding with the periodic solstices and equinoxes as well. On the other hand, there’s…

Ethan Siegel

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.

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