Seven greatest mysteries of the universe

We've made some incredible space discoveries in the last few years, like gravitational waves and liquid water on Mars.
But considering we've explored only a teeny-tiny corner of the universe, there's a lot of big questions we don't have answers for yet.
Here are some of the biggest unsolved mysteries about space.

1. What we can see makes up only 5% of the universe

Everything we can see makes up a piddling 5% of the universe. The other 95% is part dark energy and part dark matter.

If we can't actually see dark matter or dark energy, how do we know they're real? The bottom line is, we don't. Scientists think dark energy is the mysterious force that's causing the universe's rate of expansion to continue accelerating. However, dark energy could also be explained as just a big error in theory of gravity.

Dark matter is an invisible material that makes up the bulk of the matter in galaxies. Scientists think it exists because the gravitational force of galaxies is far too large to be explained by only the matter we can see. 

2. What is up with Mars?

Life may have once existed there, and it might even still exist there.
Mars used to hold vast oceans, and now there's evidence that liquid water still periodically flows on its surface.
Did this planet once hold life? And more importantly, does it hold life still? Scientists are pushing to send human explorers to Mars to find out.

3. Where do high-energy cosmic rays come from?

They are constantly crashing into Earth from outer space, but no one knows their origin.

Cosmic rays are streams of high-speed particles that fly through space and sometimes barrel into Earth. Where do they come from?

"The lowest energy cosmic rays arrive from the Sun in a stream of charged particles known as the solar wind, but pinning down the origin of the higher-energy particles is made difficult as they twist and turn in the magnetic fields of interstellar space," CERN explains.

4. What's the deal with "fast radio bursts"?

Sometimes, if an astronomer gets lucky, she can spot millisecond-long flashes of radio waves from space called "fast radio bursts" (FRBs). But just like with cosmic rays, astronomers don't know where FRBs come from.
Two recent papers have muddied the waters even more because they came to opposite conclusions about the origin of FRBs. One suggests FRBs come from the same source; the other says FRBs come from cataclysmic disasters that can't possibly repeat themselves.
The bottom line is we really don't know what causes them, and we need a better way to detect them if we want to find out.

5. Why is there more matter than antimatter?

We know that when a particle of matter and a particle of antimatter collide, they annihilate each other.
If there were an equal amount of matter and antimatter, our universe would be completely devoid of particles.
Based on what we know about cosmology, the Big Bang should have produced an equal amount of matter and antimatter. That means we would have been left with a particle-less universe. But for some reason, the Big Bang produced slightly more matter than antimatter. Something tipped the balance in matter's favor, but we have no idea what.
"One of the greatest challenges in physics is to figure out what happened to the antimatter, or why we see matter/antimatter asymmetry," CERN explains.

6. How did life on Earth get started?

It's one of the most fundamental questions of all time, and yet we don't have a scientific answer for it.
Some scientists think it was carried here on comets or asteroids. It's a good theory because we've found organic material on some them. Some even think that a piece of Mars could have landed on Earth and allowed life to get started.
Others think simple molecules caused chemical reactions to happen that eventually formed more complex molecules. Those molecules combined into things like RNA, one of the necessary ingredients for life. Then multicellular organisms evolved.

7. How will the universe end?

Astronomers estimate that in about 6 billion years, Earth will get vaporized by our dying sun. But what about the rest of the universe? 

There are a few grisly theories out there. Thermodynamics tells us that a heat death is possible, where everything in the universe becomes the same temperature. That means all the stars will fizzle out and all matter will decay. 

There's also the idea that the opposite of the Big Bang will happen. It's called the Big Crunch. If the universe keeps expanding and growing, eventually there will be too much gravity and all that gravitational force will cause everything to start contracting. 

The whole universe will shrink down into a dense, fiery inferno and we'll all get fried — putting an end to these mysteries altogether.

source: BusinessInsider

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What is the speed of gravity?

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If you looked out at the Sun across the 93 million miles of space that separate our world from our nearest star, the light you’re seeing isn’t from the Sun as it is right now, but rather as it was some 8 minutes and 20 seconds ago. This is because as fast as light is — moving at the speed of light — it isn’t instantaneous: at 299,792.458 kilometers per second (186,282 miles per second), it requires that length of time to travel from the Sun’s photosphere to our planet. But gravitation doesn’t necessarily need to be the same way; it’s possible, as Newton’s theory predicted, that the gravitational force would be an instantaneous phenomenon, felt by all objects with mass in the Universe across the vast cosmic distances all at once.

But is that right? If the Sun were to simply wink out of existence, would the Earth immediately fly off in a straight line, or would it continue orbiting the Sun’s location for another 8 minutes and 20 seconds? If you ask General Relativity, the answer is much closer to the latter, because it isn’t mass that determines gravitation, but rather the curvature of space, which is determined by the sum of all the matter and energy in it. If you were to take the Sun away, space would go from being curved to being flat, but that transformation isn’t instantaneous. Because spacetime is a fabric, that transition would have to occur in some sort of “snapping” motion, which would send very large ripples — i.e., gravitational waves — through the Universe, propagating outward like ripples in a pond.

The speed of those ripples is determined the same way the speed of anything is determined in relativity: by their energy and their mass. Since gravitational waves are massless yet have a finite energy, they must move at the speed of light! Which means, if you think about it, that the Earth isn’t directly attracted to the Sun’s location in space, but rather to where the Sun was located a little over 8 minutes ago.

If that were the only difference between Einstein’s theory of gravity and Newton’s, we would have been able to instantly conclude that Einstein’s theory was wrong. The orbits of the planets were so well studied and so precisely recorded for so long (since the late 1500s!) that if gravity simply attracted the planets to the Sun’s prior location at the speed of light, the planets’ predicted locations would mismatch severely with where they actually were. It’s a stroke of brilliance to realize that Newton’s laws require an instantaneous speed of gravity to such precision that if that were the only constraint, the speed of gravity must have been more than 20 billion times faster than the speed of light!

But in General Relativity, there’s another piece to the puzzle that matters a great deal: the orbiting planet’s velocity as it moves around the Sun. The Earth, for example, since it’s also moving, kind of “rides” over the ripples traveling through space, coming down in a different spot from where it was lifted up. It looks like we have two effects going on: each object’s velocity affects how it experiences gravity, and so do the changes that occur in gravitational fields.

What’s amazing is that the changes in the gravitational field felt by a finite speed of gravity and the effects of velocity-dependent interactions cancel almost exactly! The inexactness of the cancellation is what allows us to determine, observationally, if Newton’s “infinite speed of gravity” model or Einstein’s “speed of gravity = speed of light” model matches with our Universe. In theory, we know that the speed of gravity should be the same as the speed of light. But the Sun’s force of gravity out here, by us, is far too weak to measure this effect. In fact, it gets really hard to measure, because if something moves at a constant velocity in a constant gravitational field, there’s no observable affect at all. What we’d want, ideally, is a system that has a massive object moving with a changing velocity through a changing gravitational field. In other words, we want a system that consists of a close pair of orbiting, observable stellar remnants, at least one of which is a neutron star.

As one or both of these neutron stars orbit, they pulse, and the pulses are visible to us here on Earth each time the pole of a neutron star passes through our line-of-sight. The predictions from Einstein’s theory of gravity are incredibly sensitive to the speed of light, so much so that even from the very first binary pulsar system discovered in the 1980s, PSR 1913+16 (or the Hulse-Taylor binary), we have constrained the speed of gravity to be equal to the speed of light with a measurement error of only 0.2%!

That’s an indirect measurement, of course. We were able to do another type of indirect measurement in 2002, when a chance coincidence lined up the Earth, Jupiter, and a very strong radio quasar (QSO J0842+1835) all along the same line-of-sight! As Jupiter moved between Earth and the quasar, the gravitational bending of Jupiter allowed us to measure the speed of gravity, ruling out an infinite speed and determining that the speed of gravity was between 2.55 × 10^8 and 3.81 × 10^8 meters-per-second, completely consistent with Einstein’s predictions.

Ideally, we’d be able to measure the speed of these ripples directly, from the direct detection of a gravitational wave. LIGO just saw the first one, after all! Unfortunately, due to our inability to correctly triangulate the location from which these waves originated, we don’t know from which direction the waves were coming. By calculating the distance between the two independent detectors (in Washington and Louisiana) and measuring the difference in the signal arrival time, we can determine that the speed of gravity is consistent with the speed of light, but can only place an absolute constraint that it’s equal to the speed of light within 70%.

Source: Forbes.com

Matter

In space matter occurs in clumps which are held together by gravity. These clumps may be stars, planets, satellites, asteroids, comets, etc.

• Planets:A planet is an astronomical object orbiting a star or stellar remnant that
  • is massive enough to be rounded by its own gravity,
  • is not massive enough to cause thermonuclear fusion, and
  • has cleared its neighbouring region of planetesimals.

• Star:A star is a luminous sphere of plasma held together by its own gravity.

• Asteroids:Asteroids are minor planets. The larger ones have also been called planetoids.

• Satellite:A natural satellite, or moon is a celestial body that orbits another celestial body of greater mass (e.g. a planet, star, or dwarf planet), called its primary.

• Comet:A comet is an icy small Solar System body that, when passing close to the Sun, heats up and begins to outgas, displaying a visible atmosphere or coma, and sometimes also a tail.

Gravity

Space, in fact the whole universe consists of dimensions. There are mainly 5 dimensions:

1. Length
2. Breadth
3. Height
4. Time
5. Gravity

We live in a 3 dimensional space i.e. all the objects we see consists  of 3 dimensions (length, breadth, and height). that's what we call 3-D.

Introduction to space and universe

Many of us have heard tins phrase in our every day life.So what is your opinion about space? how would you define it? What are the various mysterious things in space? I will try to answer some of these questions in  my blog.
So... What is space?
Space is just nothing. It is a bulk area which does not contain any volume and is a absolute vacuum.

Alright guys this is my first blog. In this blog I will inform you about latest news of space and time. I will update my blog everydays.