- 3151 - UNIVERSE - size and beyond? The universe doesn't need that outside perspective in order to exist. The universe simply is. It is entirely mathematically self-consistent to define a three-dimensional universe without requiring an outside to that universe.
- ----------------------- 3151 - UNIVERSE - size and beyond?
- Despite a century of measurements, astronomers can’t agree on the rate at which the universe is expanding. How fast is the universe expanding , how big is it, really?
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- Back in 1920, Edwin Hubble first noticed the relationship between a galaxy’s distance and how fast it was moving away from us. This value, now known as the “Hubble constant of expansion“ is a key parameter in our cosmological models.
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- Hubble first measured this constant by comparing galactic distance and velocity measurements derived from a specific kind of star, “cephids“, that pulses regularly.
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- Measurements using direct methods like Hubble’s have improved greatly over the decades, but they don’t agree with methods that extrapolate from the “Cosmic Microwave Background‘ which is light leftover from the very early universe.
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- What lies beyond the boundary of the Universe? Or, what's outside the universe. We first need to define exactly what we mean by "universe." If you take it to mean literally all the things that could possibly exist in all of space and time, then there can't be anything outside the universe.
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- Even if you imagine the universe to have some finite size, and you imagine something outside that volume, then whatever is outside also has to be included in the universe.
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- Even if the universe is a formless, shapeless, nameless void of absolutely nothing, that's still a thing and is counted on the list of "all the things" and is, by definition, a part of the universe.
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- If the universe is infinite in size, you don't really need to worry about this. The universe, being all there is, is infinitely big and has no edge, so there's no outside to even talk about.
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- There is an outside to our observable patch of the universe. The cosmos is only so old, and light only travels so fast. So, in the history of the universe, we haven't received light from every single galaxy.
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- The current width of the observable universe is about 90 billion light-years. And presumably, beyond that boundary, there's a bunch of other stars and galaxies.
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- Cosmologists aren't sure if the universe is infinitely big or just extremely large. To measure the universe, astronomers instead look at its curvature. The geometric curve on large scales of the universe tells us about its overall shape. If the universe is perfectly geometrically flat, then it can be infinite. If it's curved, like Earth's surface, then it has finite volume.
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- Current observations and measurements of the curvature of the universe indicate that it is almost perfectly “flat“. You might think this means the universe is infinite. But it's not that simple. Even in the case of a flat universe, the cosmos doesn't have to be infinitely big.
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- Even if the universe is finite, it doesn't necessarily mean there is an edge or an outside. It could be that our three-dimensional universe is embedded in some larger, multi-dimensional construct.
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- Even if the universe has a finite volume, it doesn't have to be embedded. When you imagine the universe, you might think of a giant ball that's filled with stars, galaxies and all sorts of interesting astrophysical objects. You may imagine how it looks from the outside, like an astronaut views the globe of the Earth from an orbit above.
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- The universe doesn't need that outside perspective in order to exist. The universe simply is. It is entirely mathematically self-consistent to define a three-dimensional universe without requiring an outside to that universe. When you imagine the universe as a ball floating in the middle of nothing, you're playing a mental trick on yourself that the mathematics does not require.
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- It sounds impossible for there to be a finite universe that has nothing outside it. And not even "nothing" in the sense of an empty void, completely and totally mathematically undefined.
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- The entire point of developing sophisticated mathematics is to have tools that give us the ability to grapple with concepts beyond what we can imagine. And that's one of the powers of modern cosmology: It allows us to study the unimaginable.
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- An independent measurement method could help bridge the gap between methods and lead to a more decisive view of the Hubble constant as measured directly from distances.
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- That’s where the “JAGB method” comes in. Stars in the “J-region Asymptotic Giant Branch” are a specific type of aging giants that contain a substantial amount of carbon in their atmospheres that is brought to the surface by convection currents, giving them a very distinct color and brightness that allows them to be identified in a set of stars within a galaxy.
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- This makes them prime candidates for being what astronomers call “standard candles“. Because the “apparent brightness” of a star as observed depends on both its distance from the observer and its “intrinsic brightness“, knowing the intrinsic brightness of a star can allow astronomers to calculate its distance.
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- Type 1a supernovae are used to measure more distant galaxies, but they need to be calibrated by shorter range distance measurements using techniques like the JAGB method. Astronomers can not only measure the Hubble constant but also compare these various distance methods to see if there are issues with any of them.
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- Whether that new, independent value for the Hubble constant agrees with other direct measurement methods or the early-universe measurements will shed light on this question that has long puzzled astronomers and cosmologists.
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- How big is the Universe? What is the life cycle of the Universe?
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- 3143 - UNIVERSE - rate of expansion? The disagreement over the Hubble constant of expansion is one of the biggest mysteries in cosmology today. In addition to helping us unravel this puzzle, the spacetime ripples from these cataclysmic events open a new window on the universe. We can anticipate many exciting discoveries in the coming decade.
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- 3142 - UNIVERSE - is it also rotating? This Review tackles the question. Einstein’s theory of general relativity is our only validated theory of the universe as a whole. Without it we would have difficulty explaining where the universe came from and where it is going.
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- 3135 - UNIVERSE - what is it expanding in to? - If the Universe is infinite, how can infinity be expanding? Astronomers believe the Universe is finite and that eventually it comes back on itself. To explain this we have to decide the shape of the Universe. The shape is flat?
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- 3106 - UNIVERSE - The Universe you live in? Space is completely silent. Sound needs an atmosphere to travel through, and since space has no atmosphere, it has no sound. The biggest, most awe-inspiring exploding star wouldn’t even make a peep. Astronauts are able to communicate up there thanks to radio waves, which can travel through space.
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- 3101 - UNIVERSE - Is it spinning, or, is it just me? An initial spinning Universe could cause parity-violating asymmetry where gravity is allowing matter to dominate over anti-matter. Bold theories still need a preponderance of evidence. A spinning Universe is a new idea. What does it all mean?
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- 2016 - Birth of the Universe. The universe was born 13.8 billion years ago. Our telescopes can see back 13 billion years. This is when the Universe was only 800,000 years old.
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- 2008 - The universe almost did not happen. There is a fine tuning problem for many of the constants in physics. Change any of these constants only slightly and the universe we know would not have happened.
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- 1991 - Universe - what are the odds? Our whole existence appears to be n the very edge of the best conditions. Our bodies are a collection of elements that were formed inside exploding stars. So, what are the odds you are able to read this review?
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- 1493 - The universe is expanding at an ever accelerating rate due to a vacuum energy that we do not understand. This energy will eventually over come all the gravity in the universe. Enjoy life while you have it. The future is not bright.
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- 1836 - 95% of the universe is Dark Matter and Dark Energy that we do not understand. General Relativity was the theory used to detect gravitational waves. These are ripples in Einstein’s space-time.
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- 1821 - Describing the universe. The universe can be described with a model using just 6 qualities. Astronomy is a time machine that looks backwards in time. Hubble’s law describes the expansion.
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- 1808 - History of the Universe. 15 pages starts t 10^-43 seconds and goes to15 billion years. Each period details important events.
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- 1782 - Telescopes looking back in time. The Hubble Deep Space Exposure, lasting 140 hours. The view 11 billion years back in time. Expanding space stretches wavelengths into the infrared. The temperature drops from 3,000 Kelvin to -2.73 Kelvin. If the Sun were a grain of sand, the milky way would be 40,000 miles across.
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- 1759 - Why is the universe expanding? It is expanding 47,000 miles er hour for every million lightyears distance. And, it is still accelerating. On lightyear is 6 trillion miles distance.
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- 1672 - 100,000,000 years after the Big Bang the universe was 5 parts Dark Matter and 1 part Ordinary Matter, hydrogen and helium. Today Dark Energy is pulling the universe apart at an accelerating rate. We still do not understand gravity, but, Einstein’s math always works.
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- 1665 - For the first 400,000 the universe was a pea soup fog of all charged particles. The first stars could have been a million times larger than our Sun.
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- 1634 - The universe started out in the realm of Particle Physics. We are still 95% Dark Matter and Dark Energy and only 5% Ordinary matter and energy. Gravity is an amazingly small number in the scheme of things. The masses of the fundamental particles still can not be predicted mathematically.
- May 9, 2021 UNIVERSE - size and beyond? 3151
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