I’ve started thinking about what you could do with different amounts of energy, starting from the approximate amount of energy used to climb up the stairs in my school per day for the entire school. I don’t want to type out what you could do with all the different amounts of energy that I’ve calculated, so I’ll focus on how much energy you would have if you converted the entire Milky Way galaxy into energy.
(Word of advice: don’t turn the Milky Way galaxy into pure energy if you get a chance to unless the universe is ending and you’re running out of energy to sustain your civilisation. Firstly, you would destroy Earth and basically any place you would be able to call home for the next few millenia until you found another galaxy. Secondly, you would be destroyed by the sheer amount of energy released, and even if you were further away, millions of light-years away, you would probably be killed by the gamma rays released, although not for a few million years.)
The Milky Way galaxy has a mass of about a trillion Suns. Our Sun weighs 2 million trillion trillion kilograms. That gives us a mass of 2×10^42 kilograms. That multiplied by the speed of light squared gives us 1.8×10^59 joules. In case you don’t know what ^ represents, here it is. That should give you a better idea of how much energy this really is.
This might seem off topic, but it’s not. If Rapunzel’s hair grows at about 21 metres per 18 years, each year her hair would grow by 1.2metres. If she has 100,000 hairs, each of which is perfectly cylindrical with a cross-sectional diameter of 0.1 millimeters, her hair would increase in volume by 0.00377 metres cubed.
Now, assuming that polar bears consume 100,000 calories of energy per week (according to a National Geographic documentary), 1.8×10^59 joules would feed 24,751,827 polar bears for enough time for Rapunzel’s hair to grow to 40 trillion trillion light-years long, which is 430 trillion times longer than the diameter of the observable universe. It would take up about 1,255 trillion trillion trillion metres cubed of space, or 875 billion Suns of volume.
According to one source, 1 joule of energy would create 110 decibels of sound for 1 second. This means that 1.8×10^59 joules converted into energy would be equivalent to 41,662,500,416.6 Tunguska explosions(300 db) focused directly onto your ears for a trillion times the estimated age of the entire universe(the general consensus among scientists is 13.7 billion years old).
Finally, it would be enough to heat a cube of water 8 light-years on edge from 0 degrees Celsius to 100 degrees Celsius. The Sun and its neighbouring stars would fit inside that cube of water which a lot of room to spare.