Quantum Gravity

Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics, and where quantum effects cannot be ignored, such as in the vicinity of black holes or similar compact astrophysical objects where the effects of gravity are strong, such as neutron stars.

Three of the four fundamental forces of physics are described within the framework of quantum mechanics and quantum field theory. The current understanding of the fourth force, gravity, is based on Albert Einstein's general theory of relativity, which is formulated within the entirely different framework of classical physics. However, that description is incomplete: describing the gravitational field of a black hole in the general theory of relativity, physical quantities such as the spacetime curvature diverge at the center of the black hole. 

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Possible Mass of Dark Matter

  

 Sombrero Galaxy, a perfect object for calculating galaxy rotation speed. (NASA/Hubble Heritage Team/STScI/AURA)

We may not know what dark matter is, but scientists now have a better idea of what to look for.

Based on quantum gravity, physicists have worked out new, much more stringent upper and lower mass limits of dark matter particles. And they have found that the mass range is way tighter than previously thought.

This means that the dark matter candidates that are either extremely light or heavy are unlikely to be the answer, based on our current understanding of the Universe.

"This is the first time that anyone has thought to use what we know about quantum gravity as a way to calculate the mass range for dark matter. We were surprised when we realised no-one had done it before - as were the fellow scientists reviewing our paper," said physicist and astronomer Xavier Calmet of the University of Sussex in the UK.

"What we've done shows that dark matter cannot be either 'ultra-light' or 'super-heavy' as some theorise - unless there is an as-yet unknown additional force acting on it. This piece of research helps physicists in two ways: it focuses the search area for dark matter, and it will potentially also help reveal whether or not there is a mysterious unknown additional force in the Universe."

Dark matter is undeniably one of the biggest mysteries of the Universe as we know it. It's the name we give to a mysterious mass responsible for gravitational effects that can't be explained by the stuff we can detect by other means - the normal matter such as stars, dust, and galaxies.

 

For example, galaxies rotate much faster than they should if they were just being gravitationally influenced by the normal matter in them; gravitational lensing - the bending of spacetime around massive objects - is far stronger than it should be. Whatever is creating this additional gravity is beyond our ability to detect directly.

We know it only by the gravitational effect it has on other objects. Based on this effect, we know there is a lot of it out there. Roughly 80 percent of all matter in the Universe is dark matter. It's called dark matter because, well, it's dark. And also mysterious.

However, we do know that dark matter interacts with gravity, so Calmet and his colleague, physicist and astronomer Folkert Kuipers of the University of Sussex, turned to the qualities of quantum gravity to try and estimate the mass range of a hypothetical dark matter particle (whatever it may be).

Quantum gravity, they explain, places a number of bounds on whether dark matter particles of various masses can exist. While we don't have a decent working theory that unites general relativity's space-bending description of gravity with the discrete chunkiness of quantum physics, we know any melding of the two would reflect certain fundamentals of both. As such, dark matter particles would have to obey quantum gravitational rules on how particles break down or interact.

By carefully accounting for all these bounds, they were able to rule out mass ranges unlikely to exist under our current understanding of physics.

Based on the assumption that only gravity can interact with dark matter, they determined that the mass of the particle should fall between 10^-3 electronvolts and 10⁷ electronvolts, depending on the spins of the particles, and the nature of dark matter interactions.

That's insanely smaller than the 10^-24 electronvolt to 10¹⁹ gigaelectronvolt range traditionally ascribed, the researchers said. And that's important, because it largely excludes some candidates, such as WIMPs (weakly interacting massive particles).

If such candidates do later turn out to be the culprit behind the dark matter mystery, according to Calmet and Kuipers, it would mean they are being influenced by some force we don't yet know about.

That would be really cool, because it would point to new physics - a new tool for analysing and understanding our Universe.

Above all, the team's constraints provide a new frame to consider in the search for dark matter, helping narrow down where and how to look.

"As a PhD student, it's great to be able to work on research as exciting and impactful as this," Kuipers said. "Our findings are very good news for experimentalists as it will help them to get closer to discovering the true nature of dark matter."

The research has been published in Physics Letters B.

 

 Source:Science alert

 

 Sombrero Galaxy, a perfect object for calculating galaxy rotation speed. (NASA/Hubble Heritage Team/STScI/AURA)

Astronomers have discovered a star and potentially habitable planet that are strikingly similar to the sun and Earth

   

• Astronomers have discovered a potentially habitable exoplanet and its star that are strikingly similar to the Earth and the sun.
• The planet is less than double the size of Earth. The star it orbits is about the size of the sun and emits visible light.
• The system is about 3,000 light-years away from our solar system. Future space telescopes could someday study it in more detail.

Scientists have found a potentially habitable exoplanet and its star that are more similar to the Earth and our sun than any other known planet-star pair.

The planet — which is still considered a planet candidate until further confirmation — is the right distance from its star to allow for the presence of liquid surface water. That means it could potentially host life. The Earth-like world is about 1.9 times the size of our planet.

"It's the combination of this less-than-double the size of the Earth planet and its solar type host star that make it so special and familiar," Dr. René Heller, the lead author of the new study, said in a press release. Her team at the Max Planck Institute for Solar System Research described the planet and star in a paper published last week in the journal Astronomy & Astrophysics.

For now, the planet candidate is known as KOI-456.04. If its existence is confirmed by other telescopes, the exoplanet would join a group of about 4,000 known planets outside our solar system.

 

What makes an exoplanet habitable

To be considered habitable, planets must orbit a stable star at a distance that maintains a temperature suitable for liquid water.

The Milky Way galaxy could hold up to 10 billion Earth-like planets, some estimates suggest, but only about 4,000 have been identified.

The vast majority of exoplanets don't meet the conditions required for life to exist. Most of the potentially habitable worlds researchers have found orbit red dwarf stars, which aren't stable enough. Red dwarf stars are smaller and fainter than the sun, and emit infrared radiation. They also sometimes send out high-energy flares that can fry the planets around them.

The new finding came after astronomers reexamined archived data from the Kepler Space Telescope, which NASA retired in October 2018. The telescope passed the exoplanet-hunting torch to to the TESS satellite telescope, which began its observations in August 2018.  

Because KOI-456.04 is less than double the size of Earth, that could mean its atmospheric conditions are similar to ours. Plus, the star the planet candidate orbits is about 1.1 times the size of the sun, with a surface temperature of 5,200 degrees Celsius (only 300 degrees less than the sun). The star also emits visible light, like our sun does.

If KOI-456.04's atmosphere is like Earth's — meaning it has a mild greenhouse effect — then its average surface temperature would be about 5 degrees Celsius, compared to Earth's average of 15 degrees Celsius, according to the Max Planck Institute. 

by Business Insider

 

An artist's impression of exoplanet K2-18b, its host star, and an accompanying planet in the system.

ESA/Hubble, M. Kornmesser

Wormholes

 

Wormholes are solutions to the Einstein field equations for gravity that act as "tunnels," connecting points in space-time in such a way that the trip between the points through the wormhole could take much less time than the trip through normal space.

The first wormhole-like solutions were found by studying the mathematical solution for black holes.

Multiverso

 

 

 

 

 

 

 

 

 

Artistic impression of a Multiverse — where our Universe is only one of many. According to the research, varying amounts of dark energy have little effect on star formation. This raises the prospect of life in other universes — if the Multiverse exists.

Jaime Salcido/simulations by the EAGLE Collaboration

 

The Universe is all there ever was, all there is, and all there will ever be. At least, that's what we're told, and that's what's implied by the word "Universe" itself. But whatever the true nature of the Universe actually is, our ability to gather information about it is fundamentally limited.

It's only been 13.8 billion years since the Big Bang, and the top speed at which any information can travel — the speed of light — is finite. Even though the entire Universe itself may truly be infinite, the observable Universe is limited. According to the leading ideas of theoretical physics, however, our Universe may be just one minuscule region of a much larger multiverse, within which many Universes, perhaps even an infinite number, are contained. Some of this is actual science, but some is nothing more than speculative, wishful thinking. Here's how to tell which is which. But first, a little background.

 

There is a large suite of scientific evidence that supports the picture of the expanding Universe and the Big Bang. The entire mass-energy of the Universe was released in an event lasting less than 10^-30 seconds in duration; the most energetic thing ever to occur in our Universe's history. NASA / GSFC

The Universe today has a few facts about it that are relatively easy, at least with world-class scientific facilities, to observe. We know the Universe is expanding: we can measure properties about galaxies that teach us both their distance and how fast they appear to move away from us. The farther away they are, the faster they appear to recede. In the context of General Relativity, that means the Universe is expanding.

And if the Universe is expanding today, that means it was smaller and denser in the past. Extrapolate back far enough, and you'll find that things are also more uniform (because gravity takes time to make things clump together) and hotter (because smaller wavelengths for light mean higher energies/temperatures). This leads us back to the Big Bang.

There are a number of things we observe in the Universe that the Big Bang can't explain, but a new theory that sets up the Big Bang — cosmic inflation — can.

Inflation tells us that, prior to the Big Bang, the Universe wasn't filled with particles, antiparticles and radiation. Instead, it was filled with energy inherent to space itself, and that energy caused space to expand at a rapid, relentless, and exponential rate. At some point, inflation ends, and all (or almost all) of that energy gets converted into matter and energy, giving rise to the hot Big Bang. The end of inflation, and what's known as the reheating of our Universe, marks the start of the hot Big Bang. The Big Bang still happens, but it isn't the very beginning.

If this were the full story, all we'd have was one extremely large Universe. It would have the same properties everywhere, the same laws everywhere, and the parts that were beyond our visible horizon would be similar to where we are, but it wouldn't be justifiably called the multiverse.

Until, that is, you remember that everything that physically exists must be inherently quantum in nature. Even inflation, with all the unknowns surrounding it, must be a quantum field.

If you then require inflation to have the properties that all quantum fields have:

• that its properties have uncertainties inherent to them,
• that the field is described by a wavefunction,
• and the values of that field can spread out over time,

you reach a surprising conclusion.

Inflation doesn't end everywhere at once, but rather in select, disconnected locations at any given time, while the space between those locations continues to inflate. There should be multiple, enormous regions of space where inflation ends and a hot Big Bang begins, but they can never encounter one another, as they're separated by regions of inflating space. Wherever inflation begins, it is all but guaranteed to continue for an eternity, at least in places.

Where inflation ends for us, we get a hot Big Bang. The part of the Universe we observe is just one part of this region where inflation ended, with more unobservable Universe beyond that. But there are countlessly many regions, all disconnected from one another, with the same exact story.

 

 

An illustration of multiple, independent Universes, causally disconnected from one another in an ever-expanding cosmic ocean, is one depiction of the Multiverse idea. In a region where the Big Bang begins and inflation ends, the expansion rate will drop, while inflation continues in between two such regions, forever separating them. Ozytive / Public domain

 

That's the idea of the multiverse. As you can see, it's based on two independent, well-established, and widely-accepted aspects of theoretical physics: the quantum nature of everything and the properties of cosmic inflation. There's no known way to measure it, just as there's no way to measure the unobservable part of our Universe. But the two theories that underlie it, inflation and quantum physics, have been demonstrated to be valid. If they're right, then the multiverse is an inescapable consequence of that, and we're living in it.

the Multiverse is not a scientific theory on its own. Rather, it’s a theoretical consequence of the laws of physics as they’re best understood today. It’s perhaps even an inevitable consequence of those laws: if you have an inflationary Universe governed by quantum physics, this is something you’re pretty much bound to wind up with. 

 

read more Multiverse and Parallel Universe / Worlds Theory

 

 

 

 

 

Does time go faster at the top of a building compared to the bottom?

 

 

Earth's mass warps space and time so that time actually runs slower the closer you are to earth's surface. Although this is a very weak effect, the time difference can be measured on the scale of meters using atomic clocks. Public Domain Image, source: NASA. 

Yes, time goes faster the farther away you are from the earth's surface compared to the time on the surface of the earth. This effect is known as "gravitational time dilation". 

It is predicted by Einstein's theory of General Relativity and has by verified multiple times by experiments. Gravitational time dilation occurs because objects with a lot of mass create a strong gravitational field. 

The gravitational field is really a curving of space and time. The stronger the gravity, the more spacetime curves, and the slower time itself proceeds. 

We should note here, however, that an observer in the strong gravity experiences his time as running normal. It is only relative to a reference frame with weaker gravity that his time runs slow. 

A person in strong gravity therefore sees his clock run normal and sees the clock in weak gravity run fast, while the person in weak gravity sees his clock run normal and the other clock run slow. There is nothing wrong with the clocks. Time itself is slowing down and speeding up because of the relativistic way in which mass warps space and time.

Gravitational time dilation occurs whenever there is difference in the strength of gravity, no matter how small that difference is. 

The earth has lots of mass, and therefore lots of gravity, so it bends space and time enough to be measured. As a person gets farther away from the surface of the earth – even just a few meters – the gravitational force on that person gets weaker. We don't notice it much as humans, but even going from the first floor of a building to the second floor of a building moves you away from the earth and therefore slightly weakens the gravitational force that you feel. The difference in gravity between that felt at three meters above the surface of the earth and that felt at four meteres is too small to notice with our human senses, but the difference is large enough for sensitive machines to pick up.

Because the strength of gravity is weakening with every step you take up a flight of stairs, the rate at which time proceeds is also speeding up with every step. 

People who work on the bottom floor of a skyscraper are literally time traveling into the future compared to the people who work on the top floor. But the effect is very small. 

So small, in fact, that you will never notice the time difference in everyday life. People who live and work farther away from the surface of the earth are only fractions of a nanosecond ahead per year compared to those close to the surface. Though small, the time rate difference between different altitudes is real and has been measured experimentally using very accurate atomic clocks. 

The U.S. National Institute of Standards and Technology (NIST) has measured such small time rate differences and published its findings. NIST was able to measure the small time rate difference between a point on the earth and a point half a meter higher, by simply raising their experimental table a half of a meter. Their findings matched well the time dilation predicted by Einstein's relativity. 

The time dilation due to earth's gravity is significant enough that the GPS satellites, which orbit high above the earth, must adjust their internal clocks in order to take into account their faster time and therefore accurately determine the location of GPS receivers on the ground.

 source:https://wtamu.edu

 

How is time dilation due to Earth's gravity calculated?

Several points here.

1. Time itself is not affected by gravity
2. Time keeping devices however are affected by gravity and will slow down in heavier gravity. Or speed up in lower gravity

Theory of General Relativity uses formula as follows.

 

Could quantum entanglement be a result of the Big Bang?

Two particles whose properties are somehow connected are "entangled." 

Astronomy: Roen Kelly

 

If accelerated inflationary expansion occurred in the early universe, inflation itself is what puts the “bang” into the Big Bang. During inflation, the universe likely contained a chaotic soup of exotic high-energy fields. When inflation eventually ended, the energy in these fields was converted into the usual zoo of familiar particles like protons and electrons in a process called reheating.

The most common way to produce entangled states — where two particles remain mysteriously correlated regardless of distance — is when particles or fields interact or are created together. Since we believe quantum mechanics would hold during inflation, entanglement between different degrees of freedom in these exotic fields would be a natural outcome. It is an open question whether inflationary-era entanglement could survive the chaotic process of reheating.

Purely considering causality, inflation makes regions of space separate faster than the speed of light (this is allowed in general relativity). So today, regions once in causal contact during inflation are now out of causal contact, beyond each other’s so-called cosmic horizons.

The main question is whether any entanglement set up during inflation could survive and persist to somehow produce observable effects today. The answer is that we don’t know. We probably require a full theory of quantum gravity to even formulate such a question precisely. But even without knowing the details, cosmic scale tests of quantum mechanics are probably the best way to look for any strange effects. It certainly would be wonderful if the early universe left us such clues because it could let us use local measurements of space-time to test questions about parts of the universe that seem inaccessible in principle.
 

Andrew Friedman
Massachusetts Institute of Technology, Cambridge

 

Friedmann Universe Model

The "Friedmann model" is a model of the Universe governed by the Friedmann equations, which describes how the Universe expands or contracts. These equations are a solution to Einstein's field equations, and with two very important assumptions they form the basis for our understanding of the evolution and structure of our Universe. These assumptions, together called "the cosmological principle", are that the Universe is homogeneous, and that it's isotropic.

 

The cosmological principle

Homogeneity

That the Universe is homogeneous means that its "the same" everywhere. Obviously, it's not, really. For instance, under your feet is a dense, rocky planet, whereas above your head there's thin air. We live in a galaxy full of stars and molecular clouds and what not, while 100,000 lightyears from the Milky Way, there is virtually nothing. But on very large scales, say above half a billion lightyears, the Universe actually looks the same all over.

Isotropy

That it's isotropic, means that it looks the same in all directions. Again, obviously it doesn't on small scales, but on large scales, it does. If it didn't, it would mean that we occupied a special place in the Universe, and we don't think we do.

So, neither of these assumptions have to be true, but observations tell us that apparently, they are.

You might think that a homogeneous Universe would also be isotropic and/or vice versa, but that's not the case.

Three possible solutions

It turns out that, for these assumptions, there are three possible solutions to the Friedmann equation. We call the three possible universes flat, positively curved (or "closed"), and negatively curved (or "open"). Which of these possible universes we live in, turns out to depend upon the average density in the Universe, so by measuring this, we can determine the "geometry" of our own Universe. And it seems that it's "flat".

A flat universe

The reason it's called flat is that the geometry is like that of a flat 2D table, only in 3D. That is, a triangle has 180º, parallel lines never meet, etc. And it's infinitely large. Intuitively, we'd think that this is the way the Universe is, and definitely on small scales (say within our own Galaxy), it's an adequate approximation. In the 2D analogy, the 2D surface of Earth seems flat locally, and for all practical purposes the parking lot outside is flat. But if you draw a triangle from Congo→Indonesia→the North Pole→Congo, you'd measure it's sum of angles to be roughly 270º. That's because the geometry of the surface of Earth is not flat, but is "closed".

A closed universe

If the Universe were "closed", it's geometry would, in the 2D analogy, correspond to that of the surface of a ball, i.e. a triangle has more than 180º, lines that start out being parallel will at some point meet, etc. But like the surface area of a ball is finite (but doesn't have a border), so is the Universe. So if you take you spaceship and fly straight away from Earth, you would end up back here (assuming the Universe doesn't collapse before you get back, or expand too fast for you).

An open universe

If it were "open", it's geometry would, in the 2D analogy, correspond to that of the surface of a saddle, i.e. a triangle has less than 180º, lines that start out being parallel will diverge, etc. And it's infinitely large.

This picture from here visualizes the 2D analogies.

In 3D, only a flat geometry can be pictured, and this doesn't look "flat" by any means; it is simply your good old 3D ("Euclidian") space that you know from your everyday senses.

Expansion of the Universe

The Friedmann equation, together with the densities of the constituents of the Universe (radiation, normal matter, dark matter, and dark energy) tell us how the Universe expands. So, again by measuring these densities, we can prediect the evolution of the Universe. And it seems that the Universe not only expands, but actually expands faster and faster.

 Density parameters
Whether the geometry of the Universe as described above is flat, closed, or open, depends on whether the total density ρtot is exactly equal to, above, or below a certain critical threshold ρcr∼10−29gcm−3. It is customary to parametrize the density of the i'th component as Ω≡ρi/ρcr.

The Cosmic Microwave Background

The Cosmic Microwave Background (CMB) is a snapshot of the oldest light in our cosmos, imprinted on the sky when the Universe was just 380 000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. 

The top view shows anisotropies in the temperature of the CMB at the full resolution obtained by Planck. In the middle view, the temperature anisotropies have been filtered to show mostly the signal detected on scales around 5º on the sky. The lower view shows the filtered temperature anisotropies with an added indication of the direction of the polarised fraction of the CMB.

A small fraction of the CMB is polarised – it vibrates in a preferred direction. This is a result of the last encounter of this light with electrons, just before starting its cosmic journey. For this reason, the polarisation of the CMB retains information about the distribution of matter in the early Universe, and its pattern on the sky follows that of the tiny fluctuations observed in the temperature of the CMB.

Speed of the Earth's Rotation at the Equator and speed of the Earth around the sun

Questions about how fast the earth--or anything, for that matter--is moving are incomplete unless they also ask, "Compared to what?" Without a frame of reference, questions about motion cannot be completely answered.

Consider the movement of the earth's surface with respect to the planet's center. The earth rotates once every 23 hours, 56 minutes and 4.09053 seconds, called the sidereal period, and its circumference is roughly 40,075 kilometers. Thus, the surface of the earth at the equator moves at a speed of 460 meters per second  or roughly 1,000 miles per hour (1670 km/h)

Speed of Rotation = Distance/Time = 40,075 km / 24 hr = 1669,79 km/hr.

As schoolchildren, we learn that the earth is moving about our sun in a very nearly circular orbit. It covers this route at a speed of nearly 30 kilometers per second, or 67,000 miles per hour. In addition, our solar system--Earth and all--whirls around the center of our galaxy at some 220 kilometers per second, or 490,000 miles per hour. As we consider increasingly large size scales, the speeds involved become absolutely huge!

Speed of the Earth around the sun

Since speed is equal to the distance traveled over the time taken, Earth's speed is calculated by dividing 940 million km by 365.256 days and dividing that result by 24 hours to get km per hour.107232 Km/h that is equivalent to 29,78 Km/sec

 

• Mercury: 47.87 km/s (107,082 miles per hour), or a period of about 87.97 days
• Venus: 35.02 km/s (78,337 miles per hour), or a period of about 224.7 days
• Earth: 29.78 km/s (66,615 miles per hour), or a period of about 365.256365 days
• Mars: 24.077 km/s (53,853 miles per hour), or a period of about 686.93 days
• Jupiter: 13.07 km/s (29,236 miles per hour), or a period of about 11.86 years
• Saturn: 9.69 km/s (21,675 miles per hour), or a period of about 29.42 years
• Uranus: 6.81 km/s (15,233 miles per hour), or a period of about 83.75 years
• Neptune: 5.43 km/s (12,146 miles per hour), or a period of about 163.72 years
• Pluto: 4.74 km/s (10,603 miles per hour), or a period of about 247.92 years

Your Brain is Like The Universe

The human brain is literally one of the most complex structures known in the Universe – which is itself the greatest of all complexity.Your brain is the most complex organ in the universe. It is estimated to have over 86 billion neurons (also called nerve cells or brain cells), which is about the number of stars in the Milky Way Galaxy.

Each neuron is connected to other neurons by up to 40,000 individual connections (called synapses) between cells. Multiplying 100 billion neurons times 40,000 synapses is equivalent to the brain having more connections in it than there are stars in the universe. A piece of brain tissue the size of a grain of sand contains 100,000 neurons and 1 billion synapses, all communicating with one another.

The Universe is networked as well. While we may think of space as objects separated by vast tracts of…well…space, that’s not entirely the case. The Universe we see with our scientific equipment is referred to as the “Observable Universe” approximately 90 BILLION light years in diameter and containing on the order of hundreds of billions to a few trillion galaxies. These galaxies, like our Milky Way, collections of billions of stars (200 - 400 Billion) , are themselves grouped into galaxy clusters. Our Milky Way is part of the “Local Group” which contains the neighbouring Andromeda and Triangulum galaxies as well as 50 other galaxies. Those galaxies are in turn part of a larger group called the Vir

go Supercluster. The space between groups and clusters is not empty but rather hosts connecting filaments of both ordinary and dark matter that stretch for millions of light years. In this way, the Universe can be thought of as a giant network of galaxy clusters all interconnected similarly to neural networks in the brain. That network is called the Cosmic Web.

Some studies achieved by Vazz and Feletti found “remarkable” similarities between both the brain and the Universe. They also found that the networks were more like each other than other biological and physical structures including tree branches, the dynamics of cloud formation, or water turbulence.

Hereafter you can see the number of the Neurons for some animals:

Fruit Fly: 100 Thousands of neurons 

cockroach: 1 Million of neurons

Rat : 75 Million of neurons 

Cat : 1 Billion of Neurons 

chimpanzees: 7 Billion of neurons 

Elephant : 23 Billion of neurons

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How many stars are there in the Universe?

Have you ever looked up into the night sky and wondered just how many stars there are in space? This question has fascinated scientists as well as philosophers, musicians and dreamers throughout the ages.

Look into the sky on a clear night, out of the glare of streetlights, and you will see a few thousand individual stars with your naked eyes. With even a modest amateur telescope, millions more will come into view.

So how many stars are there in the Universe? It is easy to ask this question, but difficult for scientists to give a fair answer!

Stars are not scattered randomly through space, they are gathered together into vast groups known as galaxies. The Sun belongs to a galaxy called the Milky Way. Astronomers estimate there are about 100 thousand million stars in the Milky Way alone. Outside that, there are millions upon millions of other galaxies also!

Hipparcos mapped millions of stars in our galaxy, but how many more are there?

It has been said that counting the stars in the Universe is like trying to count the number of sand grains on a beach on Earth. We might do that by measuring the surface area of the beach, and determining the average depth of the sand layer.

If we count the number of grains in a small representative volume of sand, by multiplication we can estimate the number of grains on the whole beach.

For the Universe, the galaxies are our small representative volumes, and there are something like 10¹¹ to 10¹² stars in our Galaxy, and there are perhaps something like 10¹¹ or 10¹² galaxies.

With this simple calculation you get something like 10²² to 10²⁴ stars in the Universe. This is only a rough number, as obviously not all galaxies are the same, just like on a beach the depth of sand will not be the same in different places.

 

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Half the universe was missing... until now

 

In the late 1990s, cosmologists made a prediction about how much ordinary matter there should be in the universe. About 5%, they estimated, should be regular stuff with the rest a mixture of dark matter and dark energy. But when cosmologists counted up everything they could see or measure at the time, they came up short. By a lot.

The sum of all the ordinary matter that cosmologists measured only added up to about half of the 5% what was supposed to be in the universe.

This is known as the “missing baryon problem” and for over 20 years, cosmologists like us looked hard for this matter without success.

It took the discovery of a new celestial phenomenon and entirely new telescope technology, but earlier this year, our team finally found the missing matter.

Origin of the problem

Baryon is a classification for types of particles – sort of an umbrella term – that encompasses protons and neutrons, the building blocks of all the ordinary matter in the universe. Everything on the periodic table and pretty much anything that you think of as “stuff” is made of baryons.

Since the late 1970s, cosmologists have suspected that dark matter – an as of yet unknown type of matter that must exist to explain the gravitational patterns in space – makes up most of the matter of the universe with the rest being baryonic matter, but they didn’t know the exact ratios. In 1997, three scientists from the University of California, San Diego, used the ratio of heavy hydrogen nuclei – hydrogen with an extra neutron – to normal hydrogen to estimate that baryons should make up about 5% of the mass-energy budget of the universe.

Yet while the ink was still drying on the publication, another trio of cosmologists raised a bright red flag. They reported that a direct measure of baryons in our present universe – determined through a census of stars, galaxies, and the gas within and around them – added up to only half of the predicted 5%.

This sparked the missing baryon problem. Provided the law of nature held that matter can be neither created nor destroyed, there were two possible explanations: Either the matter didn’t exist and the math was wrong, or, the matter was out there hiding somewhere.

Remnants of the conditions in the early universe, like cosmic microwave background radiation, gave scientists a precise measure of the unverse’s mass in baryons. NASA

 

 

 

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