Discover Q&A
about our Universe!By Zahid Ikram
Home Index Q&A about Universe

What is the cosmic particle horizon?
The particle horizon (also called the cosmological horizon, the comoving horizon (in Dodelson's text), or the cosmic light horizon) is the maximum distance from which particles could have traveled to the observer in the age of the universe.

What is the cosmological horizon?
A cosmological horizon is a measure of the distance from which one could possibly retrieve information. This observable constraint is due to various properties of general relativity, the expanding universe, and the physics of Big Bang cosmology. Cosmological horizons set the size and scale of the observable universe.

How far away is the cosmic horizon?
If the Universe weren't expanding, the distance to the horizon would be 13.7 billion light-years. But since space gets stretched with the expansion, light waves get lift and we can see further than that: the cosmic horizon is roughly at 42 billion light-years away.

What is the Hubble sphere?
In cosmology, a Hubble volume, or Hubble sphere, is a spherical region of the Universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the Universe.

What is beyond the universe?
Astronomers think space might be infinite, with "stuff" (energy, galaxies, etc.) distributed pretty much the same as it is in the observable universe. If it is, that has some seriously weird implications for what lies out there. Beyond the Hubble Volume you won't just find more, different planets.

What is the horizon problem?
The horizon problem (sometimes called the homogeneity problem) is an observational inconsistency in the interpretation of particle horizons of FLRW models of the Big Bang. ... Two theories that attempt to solve the horizon problem are the theory of cosmic inflation and variable speed of light.

What is Comoving distance?
Commoving distance is the distance between two points measured along a path defined at the present cosmological time. For objects moving with the Hubble flow, it is deemed to remain constant in time.

Is there an edge to the universe?
We know that the galaxies must extend much further than we can see, but we do not know whether the universe is infinite or not. When astronomers sometimes refer (carelessly!) to galaxies "near the edge of the universe," they are referring only to the edge of the OBSERVABLE universe - i.e., the part we can see.

What is the universe expanding into?
The short answer is that this is a nonsense question, the Universe isn't expanding into anything, it's just expanding. The definition of the Universe is that it contains everything. If something was outside the Universe, it would also be part of the Universe too.

Where is the end of the space?
Whether space ever ends is a hard question. There is a limit to the space that we can see, because if there is stuff beyond 15 - 20 billion light years (the age of the Universe) the light from there hasn't reached us yet. So we don't know

Why the universe is expanding?
The American astronomer Edwin Hubble made the observations in 1925 and was the first to prove that the universe is expanding. He proved that there is a direct relationship between the speeds of distant galaxies and their distances from Earth. This is now known as Hubble's Law.

How is the universe expanding if it is infinite?
If, on the other hand, the universe has a finite size, then it may be legitimate to claim that there is something "outside of the universe" that the universe is expanding into. ... Therefore, the collection of galaxies (which we call the "universe") is expanding, and it is certainly fair to ask what it is expanding into.

How do we know if space is infinite?
Two possibilities exist: either the Universe is finite and has a size, or it's infinite and goes on forever. Both possibilities have mind-bending implications. In another episode of Guide to Space, we talked: "how big is our Universe". Then I said it all depends on whether the Universe is finite or infinite

What is at the center of the universe?
First, it's important to know that the big bang wasn't an explosion of matter into empty space—it was the rapid expansion of space itself. This means that every single point in the universe appears to be at the center. Think of the universe as an empty balloon with dots on it. Those dots represent clusters of galaxies.

What is beyond space and time?
BEYOND SPACE AND TIME. (Image: Ryan Wills) We don't have any trouble coping with three dimensions – or four at a pinch. The 3D world of solid objects and limitless space is something we accept with scarcely a second thought. Time, the fourth dimension, gets a little trickier.

Is space really never ending?
Most scientists think that our universe is infinite– that space goes on forever and never ends. The problem is that our universe has a finite age (the big bang probably happened 13.7 billion years age). This means that there is space that is too far away to observe or measure.

What happens when you reach the end of the universe?
The geometry of the universe is, at least on a very large scale, elliptic. In a closed universe, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch", the opposite of the Big Bang.

How fast the universe is expanding?
Using standard candles with known intrinsic brightness, the expansion of the universe has been measured using redshift to derive Hubble's Constant: H0 = 67.15 ± 1.2 (km/s)/Mpc. For every million parsecs of distance from the observer, the rate of expansion increases by about 67 kilometers per second.

What is the theory that the universe is expanding?
The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang

Is the universe infinitely large?
Current observations show that k is close to zero, which can mean either infinite or very big (much larger than 14 billions of ly which is observable space size). I treat this as it is most probably infinite. Lambda-CDM model cannot itself answer the question if the Universe is finite or not.

How does space go on forever?
Infinity in the real world: Does space go on forever? It's an existential question most of us have probably pondered at some point: is space infinite? It's tricky to answer because there's not just one kind of infinity to consider. Even if the universe goes on forever, it may not be infinitely large

What is the universe made of?
Astronomers like to call all material made up of protons, neutrons and electrons "baryonic matter". Until about thirty years ago, astronomers thought that the universe was composed almost entirely of this "baryonic matter", ordinary atoms.

How many universes are there in the world?
The fact that no one knows the answer to this question is what makes it exciting. The story of physics has been one of an ever-expanding understanding of the sheer scale of reality, to the point where physicists are now postulating that there may be far more universes than just our own.

What is the theory of inflation?
The Inflation Theory proposes a period of extremely rapid (exponential) expansion of the universe during its first few moments. It was developed around 1980 to explain several puzzles with the standard Big Bang theory, in which the universe expands relatively gradually throughout its history.

How big is the observable universe?
It is estimated that the diameter of the observable universe is about 28.5 gigaparsecs (93 billion light-years, 8.8×1023 kilometres or 5.5×1023 miles), putting the edge of the observable universe at about 46.5 billion light-years away.

How long universe will last?
According to the formulas used to calculate cutoffs, a universe that is 13.7 billion years old will reach its cutoff in about 5 billion years, his team concludes. For most people, the idea that a mathematical tool could be elevated to a real-world event might seem strange, but there are precedents for it in physics.

What will happen if the expansion of the universe continues forever?
Observations suggest that the expansion of the universe will continue forever. If so, then a popular theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario is popularly called the Big Freeze or Heat Death.

What happens when you reach the end of the universe?
The geometry of the universe is, at least on a very large scale, elliptic. In a closed universe, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch", the opposite of the Big Bang.

What does dark energy mean?
In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. ... Contributions from scalar fields that are constant in space are usually also included in the cosmological constant.

How does dark energy affect the universe?
The curve changes noticeably about 7.5 billion years ago, when objects in the universe began flying apart as a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart. One explanation for dark energy is that it is a property of space.

What is dark matter and dark energy?
The rest of the universe appears to be made of a mysterious, invisible substance called dark matter (25 percent) and a force that repels gravity known as dark energy (70 percent).

Is antimatter and dark matter the same thing?
Antimatter is the same as matter in every way, looks the same, behaves the same, except its particles have electrical charges opposite to matter. E.g., our electrons are negatively charged, whereas a positron (an antimatter "electron") is positively charged. The positron is the "anti-particle" of the electron.

What makes up antimatter?
Antimatter particles bind with one other to form antimatter, just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom.

Can we make antimatter?
Antimatter is produced in many experiments at CERN. In collisions at the Large Hadron Collider the antiparticles that are produced cannot be trapped because of their very high energy - they annihilate harmlessly in the detectors. The Antiproton Decelerator at CERN produces much slower antiprotons that can be trapped.

What is the Big Rip theory?
In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is progressively torn apart by the expansion of the universe at a certain time.

What is the big bounce?
The Big Bounce is a hypothetical cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe.

What is the possible fate of the universe?
The universe expands faster and faster, until galaxies and even atoms are eventually torn apart in the Big Rip scenario. With dark energy, the fate of the universe might go well beyond the Big Chill.

What percent of the observable universe can we see?
NEW YORK — All the stars, planets and galaxies that can be seen today make up just 4 percent of the universe. The other 96 percent is made of stuff astronomers can't see, detect or even comprehend. These mysterious substances are called dark energy and dark matter.

How many light years across is the universe?
The universe is about 13.7 billion years old. Light reaching us from the earliest known galaxies has been traveling, therefore, for more than 13 billion years. So one might assume that the radius of the universe is 13.7 billion light-years and that the whole shebang is double that, or 27.4 billion light-years wide.


Let's Explore the Universe!

Is it small or large? Is it “infinite” or does it “end” somewhere? If so, what is beyond its outer boundary? How long has it been in existence? How it is created?


Back to Home Index