relativity

9

Strange is our situation here on Earth. Each of us comes for a short visit, not knowing why, yet sometimes seeming to divine a purpose. From the standpoint of daily life, however, there is one thing we do know: that man is here for the sake of other men - above all for those upon whose smiles and well-being our own happiness depends.

The most beautiful thing we can experience is the mysterious. It is the source of all true art and science.

Happy 138th birthday to Albert Einstein, one of the brilliant fathers of modern physics and the founder of physical cosmology and relativity. 

Kányádi Sándor: Relativitás

- Megállt az idő - mondják,
akik megálltak.

- Rohan az idő - mondják,
akik rohannak.

A várakozónak: végtelen;
a rabnak: mozdulatlan;
a bölcsnek: mély;
az alkotónak: kevés;
emennek: boldog;
amannak: boldogtalan;
kecsegtető és kilátástalan,
satöbbi, satöbbi … csupa
érzelmi hozzáállás.

Einstein fölfedezése nem sokat
változtatott a közfelfogáson.

The fact that we live at the bottom of a deep gravity well, on the surface of a gas covered planet going around a nuclear fireball 90 million miles away and think this to be normal is obviously some indication of how skewed our perspective tends to be.
—  Douglas Adams, The Salmon of Doubt: Hitchhiking the Galaxy One Last Time
10

Ask Ethan: What Happens When A Black Hole’s Singularity Evaporates?

“What happens when a black hole has lost enough energy due to hawking radiation that its energy density no longer supports a singularity with an event horizon? Put another way, what happens when a black hole ceases to be a black hole due to hawking radiation?”

One of the most puzzling things about Black Holes is that if you wait around long enough, they’ll evaporate completely. The curved spacetime outside of the event horizon still undergoes quantum effects, and when you combine General Relativity and quantum field theory in exactly that fashion, you get a blackbody spectrum of thermal radiation out. Given enough time, a black hole will decay away completely. But what will that entail? Will an event horizon cease to exist, exposing a former black hole’s core? Will it persist right until the final moment, indicative of a true singularity? And how hot and energetic will that final evaporative state be?

Incredibly, even without a quantum theory of gravity, we can predict the answers! Find out on this week’s Ask Ethan.

What we don’t know about black holes:

Of all the places in the entire universe, there is probably nowhere more mysterious than the inner workings of a black hole. This is because the two most accurate theories humans have ever created disagree about what happens in the center of one.

When a large star runs out of fuel, it no longer has the energy to resist its own gravity and starts pulling in on itself. If nothing stops the collapse before a certain point, the gravity will become so strong that not even light can escape. At this point, the star becomes a black hole; a massive celestial body that has the ability to tear apart stars.

For the most part, we have a good idea for what happens in the space around a black hole. Einstein’s theory of General Relativity tells us that black holes, as well as other massive objects, bend the fabric of space and time, leading to strange events such as time dilation. But the main point of controversy isn’t what happens around a black hole, but what happens in the very middle; the singularity.

General Relativity states that if a piece of matter falls into a black hole, it gets crushed into a single point in the center. Here, any information about what fell in is completely obliterated. However, quantum mechanics tells a different story. It is a well known rule in quantum physics that quantum information can’t be destroyed, and there must be some ambiguity to a particle’s position. Clearly, something is off here.

There are a lot of different theories that attempt to solve this riddle, often involving extra dimensions or new particles beyond the Standard Model, but none of them seem to be currently testable. But it’s possible that someday, someone will give us a new, testable theory, and it will give us insight into the inner working of black holes, and maybe even the first few moments of the Big Bang.

Space fact #5

If you and I are in separate space ships both traveling fast, there’s literally no possible way to determine if I am staying still and you are moving, or if you are staying still and I am moving, or if we are both moving. Also, from your perspective time will flow normally for you and slower for me, but from my perspective time will flow normally for me and slow for you.

Basically, everything, including time, is completely relative.

The famous image of Einstein’s desk, exactly how he left it, mere hours after his death

Before his passing Einstein had refused the surgery for the internal bleeding that subsequently took his life; saying: “I want to go when I want. It is tasteless to prolong life artificially. I have done my share, it is time to go. I will do it elegantly”.

As can be seen here with the mountains of shuffled paper and scribbles on the blackboard, Einstein certainly did do his part and worked until the very end.

(Time)

10

Is Time Travel Possible, According To Science?

“You can witness the evolution and destruction of humanity; the end of the Earth and Sun; the dissociation of our galaxy; the heat death of the Universe itself. So long as you have enough power in your space ship, you can travel as far into the future as you like.”

Have you ever wondered about time travel? Perhaps you have your destination in the far future, and want to see how it all turns out? Maybe you want to return to the past, and alter the future or present by your actions there? Or maybe you want to freeze time altogether? If you want to know whether it’s possible, the physics of relativity holds the answer. Special relativity allows us to control our motion through time by manipulating our motion through space. The more we move through space, the less we move through time, allowing us to travel as far as we want into the future, limited only by our energy available for space travel. But going to the past requires some specific solutions to general relativity, which may (or may not) describe our physical Universe.

What’s the status of traveling through time? Come get the scientific story (with a brand new podcast) today!

the-endlessquestions  asked:

Does time actually exist? I personally dont think that it really exists...

Time, as described by Einstein’s theories of relativity, certainly does exist. The duration of time between two events is just as real as the distance in space between two objects, and according to Einstein, these two qualities are actually tied together. This is where the concept of space-time comes from, and it has some profound consequences.

Not only does time exist, but it can be stretched, bent, and warped. The flow of time can change depending on how fast you are moving, and how close you are to a massive object. The same can be said for space, too, but I don’t think anyone is debating how ‘real’ space is.

Now, the human perception of time may not be entirely real. Our brains aren’t perfect clocks, so we’re bound to be a little bit off. Not to mention, one can make the argument that all of human perception is an illusion, but I digress. That being said, our perception of time is a decent approximation.

anonymous asked:

I'm pretty young but I love astrophysics and I was wondering if you had any sort of list of resources (books, websites, etc) that explains and discusses quantum mechanics, the theory of relativity, and general theoretical physics.

Thanks for asking!! I’m glad that you’re interested in learning more about space and astrophysics, especially since you’re young.

I really really like PBS SpaceTime, they have a lot of SUPER interesting and very well done videos about all of the above mentioned topics (i’m actually probably gonna post some of their really good vids eventually). And when I say they have a lot of videos, I mean a LOT. And they’re all really really informative and very scientifically accurate. 15/10, would recommend. 

Fraser Cain is also pretty interesting, along with VsauceVeritasium, 3blue1brown, isaac arthur, and PBS infinite series (the math version of spacetime). You can also search these topics online and a lot of results will pop up.

In my astrophysics class, we watched several podcasts from the Silicon Valley Astronomy Lecture Series, which are in-depth talks given by professional astronomers.

If you want very in-depth articles, wikipedia is a relatively (pun intended) good source for reading about scientific topics - one of my friends jokingly said that wikipedia is where grad students record all the stuff they’ve learned so they don’t forget it in a few months (lol). Also a lot of universities have online notes and stuff posted, any website with a .edu ending is DEFINITELY trustworthy and likely to be accurate. I don’t have any book recommendations right now, but I’m going home for the weekend and I want to look at some if I get the chance. You can always find really good science books in the science section, right now I have “physics of the impossible” by Michio Kaku, and it’s a really cool book.

Let me know if you have any other questions, I’m happy to answer them and I really enjoy getting asks!

9

Earth Prepares To Snap First-Ever Image Of A Black Hole’s Event Horizon

“Instead of a single telescope, 15-to-20 radio telescopes are arrayed across the globe, observing the same target simultaneously. With up to 12,000 kilometers separating the most distant telescopes, objects as small as 15 microarcseconds (μas) can be resolved: the size of a fly on the Moon.”

One of relativity’s oddest predictions is the existence of black holes, objects so dense and massive that nothing, not event light can escape from them. But that lack-of-escaping is limited to a certain volume of space: that within the black hole’s event horizon. Although black holes have been detected and identified, an event horizon has never yet been imaged. That, however, is likely about to change when the Event Horizon Telescope comes online. Given the general relativistic prediction of the size of the supermassive black hole at the center of our galaxy – 37 microarcseconds – and the resolution of the EHT that spans the diameter of Earth, its event horizon should be visible. Speculations about black holes date back to 1783, and just a few decades after the first black hole candidate was identified, we’re now prepared to directly image one.

Are event horizons real? Get ready, humanity. We’re about to find out!

cryptoking  asked:

So this may not be possible but I thought I should ask anyway because it sounds cool. How fast would a single hydrogen nucleus (1 proton) need to be moving to inflict the same amount of energy as the nuclear bomb dropped on Hiroshima?

The energy released in the Little Boy atomic bomb was about 63 TJ, and the mass of a proton is about 1.6*10^-27 kg, so obviously this proton will need to be going very fast to get this sort of energy.

To start off, let’s see what Newton’s equations tell us. Newton’s kinetic energy equation states that KE=(½)mv^2. Plugging the numbers in, we get a velocity of 2.744*10^20 m/s, about 900 billion times the speed of light! Obviously, this isn’t correct. To get the right answer, we need to use Eisenstein’s energy-momentum relation instead.

Einstein’s energy-momentum relation tells us that in terms of energy, v=sqrt(E^2*c^2-c^6*m^2)/E. Plugging the numbers in, we get the correct answer of 0.99999999999999999999999999999999999999999999999715 times the speed of light! To compare, the fastest protons humans have ever made only go up to about 0.999999991 times the speed of light, at the Large Hadron Collider.

At this speed, the proton will have about 4*10^23 times more mass than if it was standing still, at about .0003 kg. That means that this single proton will have the mass of about a third of a US dollar bill. Although that may not sound like a lot, in terms of the rest mass of a proton, it’s absolutely MASSIVE, and I doubt humans will ever have the technology to make this happen.

whatisitwhereisit  asked:

is it true that if a person could travel at light speed, she would age differently from a regular person on earth? If so, how/what would make that happen?

In essence, yes. What you’re describing is an important element of special relativity. I’ll explain below.

We know that the speed of light is constant in any reference frame - no matter what speed you travel at, you will always observe the speed of light to be 3.00x108 m/s. Period. Since any observer will always see light traveling at this speed, it is impossible to travel at or faster than light.

So knowing this, what happens if I’m traveling at 90% the speed of light in one direction, and you are stationary? I’m going to observe light moving at  3.00x108 m/s, but so are you! Now, if I’m going at 90% the speed of light and time flows the same for me as it does for you, won’t I observe light traveling at 190% the speed you observe? Based on what we know already, this cannot happen, since that would lead to two different measurements of the speed of light, and impossibility.

In order for both of our measurements to be the same, time and space have to be different - time has to slow down for me, and my length has to shrink relative to yours, since velocity is a measure of distance over time. So you would observe me being shorter, and time flowing slower for me (so I would be moving in slow motion). However, from my perspective I am not moving, and you are moving at 90% the speed of light in the opposite direction. I observe time flowing slower for you, and I observe your length as shorter. Both observations are equally accurate, and there’s no way to prove which one is accurate - if we were to take videos of each other passing by, my video would show time flowing slower for you, and your video would show time flowing slower for me, and both are equally accurate. So yeah, that’s the basics of special relativity for you. Pretty wild, right?

Here are some resources that should help out as well, along with providing some more in-depth details that weren’t covered here; I would DEFINITELY recommend watching the two videos below. I also included graphs of time dilation, which shows how time is impacted by speed, and length contraction, which shows how length changes based on velocity.

Another post I made

TL;DR time and length have to be relative in order for the speed of light to be constant in all frames of reference. Thanks for asking, and I hope this was informative. If I went too in depth // any of it went over anyone’s head, feel free to ask me questions about it! I love answering them. Sorry this is so long, but it was the only way to explain this well.