In the Harry Potter universe, the most powerful magical artifacts or spells all seem to be very old, while there seems to be no more powerful works of magic being created in modern times.
- The Philosopher's Stone, which can transmute any metal to gold and produce the Elixir of Life, which makes the drinker immortal. However, there is only one Philosopher's Stone (Flamel's not making another one), and that was made at least 500 years ago (Flamel celebrated his 665th birthday before he died, and he would have had to create the Stone before he reached 165, as by that time he would be extremely old).
- The Resurrection Stone, created by Cadmus Peverell, had the ability to bring back an 'echo' of dead people. The only other way this is known to occur is with Priori Incantatem, where wands turned against other that share a core 'connect', and the one that loses the battle regurgitates it's last spells in reverse order. However, bringing up an 'echo' of people with Priori Incantatem only works if the losing wand has actually cast the spell that killed the people. This means that the Stone is very powerful, able to call up the 'echo' of any person (I presume... I don't think there's canon stating that it can only call up those who the user knew). This stone was created about 800 - 900 years ago, when Cadmus Peverell was alive (yes, the question refers to Ignotus Peverell, but they were brothers and they worked on the Hallows together).
- The Elder Wand was the ultimate wand of power (hey... it repaired Harry's wand when nothing else would), as well as having accumulated wisdom through the ages. This was made by Antioch Peverell, also about 800 - 900 years ago.
- The Cloak of Invisibility was the invisibility cloak, made by Ignotus Peverell 800 - 900 years ago.
Ah, but the Third Hallows is the true Cloak of Invisibility, Miss Granger! I mean to say, it is not a traveling cloak imbued with a Disillusionment Charm, or carrying a Bedazzling Hex or else woven from Demiguise hair, which will hide one initially but fade with the years until it turns opaque. We are talking about a cloak that really and truly renders the wearer completely invisible, and endures eternally, giving constant and impenetrable concealment, no matter what spells are cast at it. How many cloaks have you ever seen like that, Miss Granger?
- Hogwarts. Creating a semi-sentient castle with moving stairways and various other massive enduring enchantments (for example, the ceiling) is no mean feat. This was created by the four founders (Godric Gryffindor, Salazar Slytherin, Helga Hufflepuff and Rowena Ravenclaw) "over a thousand years ago", although the exact date is unknown.
- Horcruxes are cursed objects that contain a 'consciousness backup' that prevent actual death as long as they exist. Created by Herpo the Foul more than 2000 years ago, they are indisputably evil, but also indisputably magically powerful.
Whereas in modern times, the most powerful magical artifacts or spells seem to be all products of Weasley's Wizarding Wheezes, staffed by a pair of drop-out mischief-makers.
Also, no-one is able to recreate any of the artifacts, otherwise they would have, as they are highly desirable items.
This is totally different to Muggle history, which is one of increasingly powerful inventions and discoveries. Sure... there's still pyramids in Egypt that we don't know how they were built at the level of technology of the builders thousands of years ago, but if we wanted to, we could recreate them with our level of technology... faster.
However, modern wizards don't know how the artifacts were created with the level of technology of the ancient wizards, and they are unable to recreate them with their current level of technology.
There seems to be a lot of magical knowledge lost over the years, leading to a decrease in the power of magical creations. Why was this knowledge lost?
(It's not because of the HPMOR Interdict of Merlin...)
Ancient wizards made really powerful things. Modern wizards don't and can't make similar really powerful things.
There's obviously been a loss of magical knowledge.
What is the reason for this loss?