# PBS_SpaceTime

8m17s

## Groundbreaking Explanation About How A Circle Can Be A Straight Line

General Relativity! Spacetime! And... curved lines? On this week's episode of Spacetime, Gabe talks about what it actually means for a line to be straight so we can better understand what we mean by the idea of "Curved Spacetime". To make it easer he will divide this ground work at three parts: Part one: Geometry, part two: Spacetime, part three: Spacetime + curvature. This is part one of our series on General relativity, so be sure to check it out! Part one is about straight lines and curved spaced, no physics. Gabe gives great explanation about how a curve can be “straight” if tangent vectors stay tangent when parallel- transported along with that curve. Simple, isn’t it? This is great example with an ant confined to the surface of an ordinary sphere with no concept of or an access to the direction off the surface. From the ant’s two dimensional confined prospective, curve one between A and B is straight. The vector tangent to curve one at point A remains tangent all along curve one as we parallel transport it to point B. Once the ant does that over lots of curves joining A and B it finds that the tangent vector will remain tangent only. That segment is called a geodesic and piecewise it’s straight. Topology is global, but geometry and curvature are local. Now what we have learned from Gabe is that in a three dimensional space you can test curvature just by moving a vector parallel to itself around a circle. If you end up with the same vector you started with space is flat, if not, it’s curved.

8m32s

## Here Are 5 Ways To Prevent A Killer Asteroid From Colliding With The Earth

When it comes to dangerous asteroids striking Earth, it's not a matter of if, it's a matter of when. We have begun to track projectiles large enough to destroy our planet, and we are in the clear for the foreseeable future. However, there are countless asteroids large enough to take out an entire city that we cannot see. If you’ve ever watched the movie Armageddon, you know what we are talking about. There is a high probability that sometime in the future we would have to resort to those kinds of actions to save our planet. There is a reason to believe that it hasn’t been the first time an asteroid of large proportions changed the course of history when it fell on the Earth and wreaked havoc on it. The dinosaurs as species were wiped of the face of the Earth by an asteroid that hit the coast of the Yucatan peninsula, triggering a series of changes in the Earth’s climate and biodiversity. The first thing to do when under the threat of an asteroid hitting our only home is trying to locate it sooner rather than later. Efforts have been made to scan as much of the dark sky for flying rocks that are bigger than 500m, so that we are aware of their approach, but it’s still unclear as to where those smaller than 500m are. They are just like a grain of sand in the vastness of space. Other ways of dealing with them include finding a way to change their trajectory, whether by kinetic or gravitational force.

10m59s

## Guide-Through To How To Build A Black Hole

Earth mysteries are a wide range of spiritual, quasi-religious and pseudo-scientific ideas focusing on cultural and religious beliefs about the Earth, generally with regard to particular geographical locations of historical significance. Believers in Earth mysteries generally consider certain locations to be "sacred", or that certain spiritual "energies" may be active at those locations. The term "alternative archaeology" has also been used to describe the study of Earth mystery beliefs. A black hole is a region of space-time exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform space-time to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed. In many ways a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved space-time predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe. Black holes have mystified physicists for decades, but with the help of quantum mechanics, we are beginning to make serious progress in understanding these strange objects. This week on Space Time, Matt dives deeper into the physical process of creating a black hole, and what that can tell us about how black holes behave. Take a look as this video is sure to broaden your horizons!

10m34s

## Intriguing Theory About Alien Life And Earth-Like Planets

With millions of Earth-like planets around sun-like stars in our galaxy alone, why don't we see intelligent alien life? Or any other life for that matter? It gets especially weird when you factor in new scientific revelations that life on Earth occurred crazy fast! So if you want to help us theorize on the real reasons we haven't found alien life, you should check this video of Space Time! Why don’t we see alien civilization? The resolution for it has to be that there is some sort of great filter that either makes intelligent life extremely rare in the first place or that wipes out, essentially, all advanced civilization before they get to the galactic empire stage, whether by a nuclear war, environmental catastrophe, accidentally making a black hole that swallows the planet, et etcetera. But some people believe in that and some people just don’t buy that theory. The other logical explanation is that we know of exactly one instance intelligent life happening, the case of the earth. Multicellular life evolved independently dozen of times. It just took a really long time for those single cells to become complex enough to form large collaborative structure capable of collective reproduction, I.e plants, animals, species capable of making the Kerbal Space Program. So what is the great filter? Maybe it’s just time. If life is common then of the billions of Earth-like planets in the galaxy , only a tiny fraction needed to have a small head start on us in order to have produced the Federation of Planets and Stargates and stuff by now. Well, that explains a lot!

11m23s

## S2 Ep28: What Happens at the Event Horizon?

What really happens when you approach the event horizon of a black hole?

8m44s

## Will Mars or Venus Kill You First?

Humans have been talking about space colonization for quite some time, but our neighboring planets are not exactly the most hospitable places. If we are ever going to be successful, we should probably figure out where we could reasonably expect to survive.

9m58s

## Strange Stars

What happens when matter can’t get any denser yet somehow does? The answer - it becomes strange. Strange Stars may be the most massive stellar remnant that is just shy of forming a black hole. And they could be even cooler than black holes.

11m51s

## Do Events Inside Black Holes Happen?

Black holes! From Stephen Hawking to Interstellar, black holes are mammoths in the world of science AND sci-fi. But what exactly IS a black hole? Do events happen inside black holes? Are black holes really a hole? Are black holes really black?!

8m23s

## The Real Meaning of E=mc²

You’ve probably known OF E=mc² since you were born, and were also probably told that it meant that it proved Mass equaled Energy, or something along those lines. BUT WAIT. Was E=mc² explained to you properly? Mass equalling energy is mostly true, but E=mc² actually describes a much more interesting aspect of reality.

10m48s

## Why is the Earth Round and the Milky Way Flat?

Our universe is not a very diverse place when it comes to shapes. Large celestial bodies become spheres, galaxies become discs, and there is little room for variation. Why is this? Well it turns out physics has some pretty strict rules when it comes to creating new planetary bodies.

8m04s

## When Time Breaks Down

We learned how motion gives matter its mass, but how does motion affect time? Let’s dive deeper into the true nature of matter and mass by exploring Einstein’s photon clock thought experiment, and the phenomenon that is time dilation.

12m25s

## S3 Ep16: White Holes

Lurking in the depths of the mathematics of Einstein’s general relativity is an object even stranger than the mysterious black hole. In fact it’s the black hole’s mirror twin, the white hole. Some even think that these could be the origin of our universe.

9m49s

## S2 Ep26: Strange Stars

Neutron stars are made of a substance known as Neutronium. It was thought that this was the densest form of matter possible but some theoretical physicists believe that at the core of some neutron stars the Neutronium breaks down even further, into quark matter. It may even evolve one step further into “strange matter", the densest and most stable substance in the universe.

7m44s

## What Happens At The Edge Of The Universe?

Lots of people believe the Universe is infinite, but there's a good possibility that might not be the case. Which means that there would be an actual edge of the Universe. What happens at that edge? Is there a restaurant?

7m43s

## Does Dark Matter BREAK Physics?

In this episode, welcome in Matt O’Dowd as the new host to rigorously take you through the mysteries of space, time, and the nature of reality. We’re starting off this new season with perhaps one of the most mysterious things of all — DARK MATTER. What is it? Where does it come from? And is it even real? Watch this episode of Space Time to find out!

11m10s

## S2 Ep23: The Many Worlds of the Quantum Multiverse

The Copenhagen interpretation of quantum mechanics tells us that observation collapses a probability wave into a single definitive outcome, but this isn’t the only interpretation of quantum mechanics. The many worlds theory proposes that the wavefunction never actually collapses. The observer simply follows one of those many possible paths into their present reality while all the other paths conti

8m35s

## The True Nature of Matter and Mass

Are matter, mass, and time real?

10m34s

## S3 Ep18: The Future of Space Telescopes

The Kepler mission has determined that terrestrial planets are extremely common, and may orbit most stars in the Milky Way. But these planets are difficult to directly image because they’re dense and small. Our Sun is about ten billion times brighter than Earth. Train a distant telescope on us, and it will be overwhelmed by the Sun’s rays. So how can we find terrestrial planets around stars light

10m41s

## S3 Ep5: Supervoids vs Colliding Universes!

If you study a map of the Cosmic Microwave Background, or CMB, you may notice a large, deep blue splotch on the lower right. This area, creatively named the Cold Spot. Is this feature a statistical fluke, the signature of vast supervoids, or even the imprint of another universe?

10m28s

## S2: The Quantum Experiment that Broke Reality

The double slit experiment radically changed the way we understand reality. Find out what the ramifications of this experiment were and how we can use it to better comprehend our universe.

9m53s

## S2: Is Quantum Tunneling Faster than Light?

Where are you right now? Until you interact with another particle you could be any number of places within a wave of probabilities. Matt dives into these counter-intuitive ideas and explains the bizarre phenomenon known as quantum tunneling in this episode of Space Time.

12m11s

## S2 Ep8: Is an Ice Age Coming?

We’re living in a brief window of time where our planet isn’t frozen underneath a giant layer of glaciers. How much longer will the moderate climate that we’ve come to know as “normal” continue? This episode looks at how the changes in our planet’s orbit and rotation impacts our climate.

2m21s

## The Leap Second Explained

Every once in a while we add a second onto our days. Similar to the Leap Year, this is known as the Leap Second. But, if the Leap Year already helps us account for the offset from a calendar in days, what exactly does the Leap Second do? Check out this video for the answer!

10m17s

## Is Gravity An Illusion?

Most of us take gravity as an assumed part of our living realities, but why? Basic physics introduces us to the concept of gravity from a Newtonian sense, but when you start factoring Einstein into an understanding of gravity, things get weird. For example, gravity may simply not exist. Why? Watch this week’s episode of PBS Space Time and find out why gravity may be an illusion!

11m27s

## S3 Ep17: Neutron Stars Collide in New LIGO Signal?

Last year LIGO announced the detection of gravitational waves from the merger of two black holes. The science world went a little crazy. Only a few weeks ago a new rumour emerged: that LIGO had, for the first time, spotted gravitational waves from the collision of a pair of neutron stars. If it’s true, some long-standing astrophysical mysteries are about to be unlocked.