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.



Gravity wells - 

A Gravity well or gravitational well is defined as “a conceptual model of the gravitational field surrounding a body in space.”

The more massive the body, the deeper and more extensive the gravity well associated with it. The Sun is very massive, relative to other bodies in the Solar System, so its gravity well appears “deep” and far-reaching.

(picture a very heavy object sinking deep into a bed mattress; the more mass the object has the deeper it sinks in and creates a deeper sinkhole; a deeper sink hole will pull in any nearby objects towards the centre object with greater influence. Objects of  mass bend the fabric of spacetime this way also as the theory of general relativity explains) 

a video example

I was just wondering how many hours of existence 36-year-old John has left, and it got me thinking. youve-got-your-love-online, who lives in a very different time zone from me, reminded me that it’s John’s birthday, and I was like, “wait, no, it’s tomorrow” because here it’s still Saturday. But John’s actual age has nothing to do with what time zone any of us live in now, including John. Your age doesn’t change as you change time zones, it’s completely dependent on what time it was (and where you lived) when you were born. Unless of course you’re travelling over time zones at light speed. 

Seeking SciNote, Physics: The Speed of Light and Time Dilation


I heard, in an episode of a popular Brazilian podcast, some physicists say that if one were to travel at 100% the speed of light, they would witness the end of the Universe. Why is that, and what supports this hypothesis?

Asked by Anonymous

Answer: Before we get to the speed of light, let’s look at one of the central equations of special relativity: the one describing time dilation.


Hyperphysics, an excellent website if you’re ever doing a physics problem and stuck – or if you’re just curious about physics and would like to know more – has a much more detailed version of this same equation:


I show both of these because I think the first equation is clearer but the second website is more straightforward. Let’s go through them slowly. Say that you’re in a car going at some speed that we’ll call “v”. This v, if you’re on Earth, is going to be pretty small, but in a minute we’re going to break the rules of Earth in order to have a little fun. On the top of the right side of the equations is what is labelled Tb and T0. This is the amount of time that you measure as going by in your car. Nothing weird so far; you’re just sitting in your car looking at your watch or your phone or counting heartbeats. It doesn’t matter how you’re keeping track of time, just that you are. On the left side of the equations is that TA or T. This is the amount of time that someone would measure if they were sitting on the ground as your car is going by. Normal common sense says that for every second you count off in your car, someone on     the ground should count exactly one second. It’s so obvious that that sentence reads as if I’m trying to trick you, but I’m not. We think of ourselves as in a domain of absolute times, where one second is one second no matter what we’re doing or how we’re moving.

Except this isn’t true, and it’s not the way the universe works. There’s that factor with the square root on the bottom of the right-hand side of the time dilation equation, which has a “v” in it. This is what physicists have agreed to call “gamma”, and it looks like this:


This means that as your velocity increases, every car-second counts for a little more than every ground-second. In other words, time goes by more slowly when you’re moving than when you’re standing still. Let’s put in a few numbers to see how much of an effect this has.

Typically a car on the highway goes about 60 miles per hour, which is about 30 meters per second. At that velocity, for every second of car time, 1.0000000000000049 seconds of ground time pass.
But that’s .000005% the speed of light. Let’s break the speed limit – also maybe the sound barrier – and travel at 10 times that velocity. At 300 meters per second, T (ground time) = 1.0000000000005 * T0 (car time). Okay, still not much. What about 1000 times that velocity? This is 300,000 meters per second, or .1% the speed of light. T = 1.000000500000375 * T0. That’s something, but still not much. Who’s going to notice 500 nanoseconds?

Ramp it up again to 3,000,000 meters per second – 1% the speed of light. T = 1.0000500037503124 * T0. 50 microseconds – still not much.
Let’s go to half the speed of light. T = 1.1547 * T0. Now that’s something noticeable; ground time is off from car time by more than 10%. At 75% the speed of light, T = 1.51186 * T0. At 90% the speed of light, T = 2.29416 * T0. Now every second of car time is two seconds of ground time. Finally, at 99.9% the speed of light, T = 22.36627 * T0, meaning that your clock is running 22 times more slowly than the clocks on the ground, just because you’re moving.

Okay, this is all good and fun, but I haven’t gotten to your question. Let’s see what happens if we put the speed of light into this equation. Well, (v^2)/(c^2) becomes (c^2)/(c^2), which is equal to 1. 1-(c^2)/(c^2) = 1-1 = 0. T0/0 = the end of life, the universe, and everything. You can’t divide by zero; it’s common enough knowledge that there’s a whole web of memes based on it. So how do we interpret this? Well, notice that as we got closer to the speed of light, your time was passing more and more slowly – exponentially more slowly, really. It follows this graph:


The logical conclusion is that for a body traveling at the speed of light, one second of car-time is an infinite amount of ground-time. This is the justification for saying that if one were to travel at the speed of light, one would see the end of the universe. It’s because if you travel at the speed of light, no time passes for you, but an infinite amount of time passes around you. I’m curious why only some physicists would say this, though, because it’s very well-established. Maybe the others are too busy saying “You can’t get to the speed of light because it would take an infinite amount of energy to do so” to entertain a fun hypothetical.[1]

Now to the proof. Wikipedia has a whole page on “Tests of Special Relativity” that I think is worth browsing. I’ll just say that we don’t have direct evidence that traveling at the speed of light will allow one to witness the end of the universe, for some definitions of direct. Obviously the universe hasn’t yet ended and it’s impossible to travel at the speed of light, so we’re doubly blocked. However, science doesn’t need to work by direct measurements like that to know that its conclusions are very likely. Your GPS works because of special and general relativity. Muons in the atmosphere take longer to decay than they should because of special relativity. Mass dilation is something they need to take into account at the CERN. Relativity is weird, but it’s real nonetheless.

Thanks for your question!

[1] It would take an infinite amount of energy because mass dilates the same way time does. So at 99.9% the speed of light, if you started out weighing 100 kg you would instead weigh 2,200 kg, and it goes up exponentially in the same way. The energy it takes to move something is the mass times the square of the velocity, so as both of those get really big, so does the energy it takes to push you more. Relativity is weird.

Answered by Brendan C., Expert
Edited by Dylan S.

Happy Birthday, Albert Einstein!

Born March 14, 1879, in Ulm, Germany, Albert Einstein (1879−1955) seems not to have anticipated how famous his theories and ideas would make him. And as you see from the quotation in the image above, Einstein professed to be mystified by the adulation and attention that rained down on him as his last name became, even during his lifetime, a byword for “genius.”

The truth is, however, that his life and work continue to intrigue. After all, as the Museum's Einstein exhibition (on display in 2002−2003) points out, “Albert Einstein reinterpreted the inner workings of nature, the very essence of light, time, energy, and gravity. His insights fundamentally changed the way we look at the universe—and made him the most famous scientist of the 20th century.”

More on the man and his ideas.

Scientists studying cosmic microwave background (the faint afterglow of the Big Bang) have detected a signal generated a trillionth of a trillionth of a trillionth of a second after the Big Bang began.  They’ve found gravitational waves – ripples in the fabric of space-time.  Physicists are especially excited (and they’re trying their best to get their non-physicist friends excited too) because studying these waves could help bridge the divide between our understanding of gravity and quantum mechanics. You can hear more about it here.

Image credit: This is the telescope they used to detect the gravitational waves.  It’s called the South Pole Telescope, and it was photographed by Eli Duke.


Ask Ethan #74: Gravitational Waves

“Dear Ethan,
What the heck are gravity waves?

When you think of waves, chances are you think of some type of pressure wave moving through a medium, like sound or water waves, or you think of light, which is an electromagnetic wave that requires no medium to move through. But there’s another type of wave that exists, that no one expected before Einstein came along: gravitational waves. These are energy-carrying ripples through the fabric of space itself, explained in a beautiful analogy with light and detailing how they affect our Universe as well as how to detect them.