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Time moves slower on Mercury than it does on Earth.
A day on Mercury is 58 days, 15 hours and 30 minutes on Earth.
We can tell this by observing Mercury through telescopes and timing how long it would take
for Mercury to complete one full orbit around the Sun.
However, if we travelled to Mercury and started our timer there, we would not get the same
figure.
This is because time does not move as constantly as you might think.
It can be affected by speed – the faster you go, the slower time goes for you.
But it can also be affected by gravity.
And Mercury is much closer to a massive source of gravity in our solar system – the Sun.
But, how much does gravity affect time?
Could we live to incredible ages if we all went to live on Mercury?
I’m Alex McColgan, and you’re watching Astrum.
Join with me today as we answer this question, and explore the strange and warping world
of general relativity, and gravitational time dilation.
I hope by the end of this video to have earned your like and subscription.
To begin with, what exactly is time?
Mark Twain once said that time is what keeps everything from happening all at once.
It separates yesterday’s events from today’s, and today’s from tomorrow’s.
As you sit here and watch this video, you are not doing what you were doing yesterday,
or tomorrow, you are watching this video.
You are constantly travelling through time in the direction of the future, at a rate
of 1 second per second.
This is the normal speed for travel through time, and is shared by you and everyone else
on the planet.
But this speed doesn’t have to be the case.
As discovered by Albert Einstein, the faster we travel through space, the slower our time
becomes, up until the point where if we somehow could travel at the speed of light, time would
stop moving for us.
If we were to travel to an object 4 light years away from us, to people here on Earth
it would look like it took us 4 years.
To us, it would look like we arrived at our destination instantaneously.
Although it sounds incredible, scientists have proven that this actually happens.
They took 2 clocks.
One they put one on a plane and flew around the world with it onboard, increasing its
speed for an extended amount of time, while leaving the other one at a stationary location.
When they eventually returned and compared the clocks again, they found that the clock
that had travelled faster had actually recorded less time, in line with what general relativity
had predicted.
General relativity is a real thing.
But Einstein also predicted that this would happen with gravity.
The closer you are to a large source of gravity, and the more mass that source of gravity has,
the slower time will go for you.
This was proven to be correct in 1959 with the Pound-Rebka experiment, where they shot
gamma rays from the top of a tall building to the bottom, and recorded whether anything
had happened to the light waves.
They found that the frequency of the waves increased the closer to the earth they were.
Kind of like cars bunching up in congested traffic, the peaks of radiation moved closer
together.
Time slowed down ever so slightly for the gamma radiation the closer it got to the Earth.
This effect is significant enough that satellites have to be programmed to account for it, because
when they are further away from the Earth’s gravity, time moves more quickly for them.
Without this correction, their internal clocks would go out of sync with our clocks on Earth,
which could cause problems.
And yes, that’s right, the Earth’s gravity is enough to cause time to slow down for us.
So, you’re probably now thinking, how much faster would time be going for me if I wasn’t
on Earth, or if Earth had no gravity?
Well, it’s a matter of perspective.
The procession of time will always appear the same from your perspective, you won’t
feel like you’re going slower, although you may notice some weird stuff going on around
you.
It’s the outside observer that has to deal with you slowing down.
To find out an exact answer to the question, Einstein devised the following equation: We
will be using this equation a lot in the rest of the video, so let’s try to understand
it.
It looks a little scary, but it’s not as bad as it looks.
“t0” is the answer we’re looking for – how much time would pass on the object
we’re interested in, in this case the Earth.
“tf” is how much time would pass in a place completely unaffected by gravity.
Such a place doesn’t exist, by the way.
But it is our hypothetical, stationary clock.
“G” is the gravitational constant – a number they added to basically make the sums
work out.
We’re not going to worry about where it came from, all we’re interested in is the
fact that it’s always this: 6.6743x10-11 N*m2/kg2.
Don’t worry too much about the metric at the end.
“M” is mass, specifically the mass of the object creating the gravity.
“r” is the distance from the centre of that object, and “c” is the speed of light,
a figure we know to be 299,792,458 m/s.
So, to find out how much slower time goes on Earth compared to somewhere where there
was no gravity, all we have to know is how much mass the Earth has (5.972 × 1024 kg),
how far we are from its centre (6,371,000m), and then we can just decide how much time
we want to compare.
Just to ease ourselves in, I decided to try this formula out with 60 seconds.
If 60 seconds passes in our place unaffected by gravity, how much time passes on Earth?
I plugged in the information and got our result: t0=59.99999996…s.
For every 60 seconds that passes, people on Earth experience only 59.99999996 seconds.
In other words, 6,000,000,000 (6 billion) seconds have to go by before we notice a difference
of 4 seconds.
This happens roughly once every 190 years.
So realistically, you’ll only gain about 2 seconds over the course of your entire lifetime
because of the Earth’s gravity compared to a place with no gravity.
This is… a little underwhelming.
However, we here on Earth are not just affected by our planet’s gravity.
We are also affected by the gravity of the Sun, which in terms of our equation is much
more significant.
So, let’s try this again by inputting the mass of the Sun (1.989 × 1030 kg, or 1,989,000,000,000,000,000,000,000,000,000
kg), and our distance from it (147,490,000,000 metres) into our equation.
This gives us the new figure.
How much time goes by for us on Earth for every 60 seconds of actual time that goes
by? 59.9999994…s.
While this is a more significant number, it does mean that you are only seeing a difference
of a second once every 3 years or so.
Or in other words, about 24 seconds over the course of an average human lifetime.
But Mercury is much closer to the Sun than Earth.
Surely time is significantly altered here compared to Earth with a massive object like
the Sun so close-by.
How much more does time slow down for us on Mercury?
The equation is essentially the same as before – the only new number we need is the distance
between the Sun and Mercury (69,813,000,000 metres).
The answer to our final question of “how much time passes on Mercury every 60 seconds”
is: 59.9999990...s.
60,000,000 seconds need to go by before there’s a single second’s difference.
This happens roughly once every 1.9 years, which scaled up across a lifetime equates
to about 38 second’s difference.
Only 14 more seconds than Earth.
But from your point of view, you’re not even really gaining those seconds, because
from your perspective time would be moving normally.
It would be the Earth that is moving ever so slightly faster from your point of view.
So, if you pointed a telescope towards Earth, you’d just see 14 more seconds of Earthen
history than you would if you were living there.
As Mercury is fairly inhospitable, this probably isn’t worth it.
So, does Mercury’s proximity to the Sun allow time to move slower for you compared
to Earth?
Yes.
But only by a difference of about 14 seconds over your entire lifetime.
In reality, time dilation due to gravity is not actually that significant.
At least, not in our own solar system.
The mass of the Sun is not enough to really stretch time that much for us, even if we
were as close to it as Mercury.
The Sun would need to be millions of times more massive before we would begin to experience
time dilation to any significant degree.
However, it’s still a fascinating insight into the way that time flows in our universe,
and reveals that time is not as constant as we might think.
And of course, it begs one final question.
Are there any objects in our universe that are massive enough that we’d experience
significant time dilation around them?
There are.
And this is where things start to get very noticeable to an outside observer.
At the centre of galaxies exist objects known as supermassive black holes.
These objects have masses that are millions to billions of times the mass of our Sun.
In other words, if you were to fall towards them, time could slow down for you so much
that it would approach 0.
If you were to get close enough to one of these giants and later escape it, you could
spend half an hour around there and emerge to find that hundreds of years had passed
to the people back on Earth.
People on Earth with a powerful enough telescope would see you barely move, even your breathes
would take days to complete.
In fact, there would be a point right at the edge of such a body that as you approached
it, your time would hit 0.
What would happen if you passed that point?
Our equations break down, and so cannot explain what lies beyond that horizon.
Science does not yet have the answer, although there are certainly many theories.
But that might be a subject better explored in another video.
General and special relativity can be pretty confusing topics, but was this video good
at helping you digest this topic?
And is this something you’d like to know more about?
Let me know in the comments below, and if you found value in the video, please consider
giving it a like and subscribe.
Now, if you like thinking in hypotheticals like in this video, here’s something we’ve
probably all thought about before: what if Earth suddenly became uninhabitable?
It’s something that will definitely happen at one point or another, and the only real
solution to this possibility is space colonies.
I’ve been watching this series called “Space Colonies”, where they explore the options
for humanity that we could achieve in the not to distant future.
And that’s the fascinating thing, this isn’t as distant a prospect as some people may think.
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