In The Dresden Files universe is there a limit to what magic can do ? And how does it compare to other magic in different series like harry potter for example?
There are no theoretical limits. Magic can, given enough of a power source and a properly constructed spell, do literally anything. The Laws of Magic are a simple enough guide to the possibilities; magic can warp minds, alter flesh, kill by the droves, and even rewrite time and space.
Once active, however, a spell still has to work in the "real world", so to speak. Physics plays more of a part than you'd expect. For example, let's take Harry's favorite fireball. You can build that spell to just directly create heat for the fire, but that's pretty exhausting on the magic. You could also build the spell to just move nearby heat around, stealing it from other sources to make the fire hot. That's a lot less intense on the magic, but might make it harder to do in a frozen tundra. Point is the heat for that fireball has to come from somewhere. Magic doesn't provide a free lunch, just lets you bend how to pay for it.
If you wanted to do something catastrophic, like alter history, the energy involved becomes insane, fast. Really, time only flows in one direction, and we haven't figured out any rules that change that on Earth. So every ounce of power you get would have to fight the natural order of the weight of time, just to get into the past, even slightly. Then the spell would need more to change whatever you needed, more to make things flexible enough for the timeline to accommodate, more, more, more.
So practice reigns rather than theory and the effort involved in bending the world to your whims usually wouldn't work out. A single wizard can only channel so much power on their own. Gathering more would require focuses for something elses energy, places to store the energy up, preparation, more time, etc.
The biggest magics seen actively so far in the series -
Kemmlers Darkhallow and the Red Court's bloodline slaughter
are usually shortcuts past all that, using some form of human sacrifice to harvest life energy by the truckload.
There are beings that can break the practical boundaries, but by and large they exist under their own laws and natures (or laws of nature) and are constrained from large scale meddling. Examples include -
Nicodemus' pentagram traps, which per Harry needed some sort of divine level of Hellfire to work and implied the involvement of Lucifer, but which in turn allowed certain archangels to interfere to counterbalance his influence; also Mab altering weather patterns and invoking an early Winter in Chicago in the same book, which falls under her perview as Winter Queen.
To answer the Harry Potter question, it looks like the other answers have it pretty well covered. As used up-front in the Harry Potter books, magic is a very structured regulated and known quantity, and while there's deeper effects related to intentions they don't get into that much. Magic in The Dresden Files is fueled by life and emotion and energy, but it's form and effects is only limited by the wizard in question, his/her resources, and imagination.
tl;dr: So far we have not seen any limit to what magic is capable of doing, so long as the magic user has the skill, strength, and talent to channel enough magic to do it.
Compared to, e.g. the Potterverse, magic in the Dresden universe appears way more powerful, though I don't know that anyone in Harry Potter ever really tested the limits of what they can do. Potter-style magic is more structured: spells require wands and magic words and such, which may be the limiting factor there; Dresden-style magic is completely internal, and the words and wands and such are merely use to aid the spellcaster, and are not required.
There are actually a number of different kind of magic in the Dresden Files universe, with different characteristics.
Most of the humans and semi-humans in the series use a standard form of human magic that relies on two things:
- The naturally-occurring "magic energy" in the environment, and
- The ability of the wizard to channel it through their body.
We have seen wizard-type characters perform some pretty impressive effects (in particular, read the battle with the Red Court at the end of Changes). The only limit to their effects seems to be the practical limits of the wizard's body more than anything else. After using lots of high-powered spells, Harry is often exhausted and unable to conjure up anything strong anymore. This is also why wizards use so many objects: they are focus devices, allowing them to perform stronger effects with less effort.
The other kind of human magic we see is "blood magic", used by the bad guys. In this case, the wizard uses human sacrifices to build up a lot of power very quickly, without their needing to gather it into themselves first, thus making the process easier. Again, the climax of Changes shows perhaps the biggest example of this so far: a single blood-powered spell was able to
instantly destroy every single Red Court vampire in the world.
which is a pretty damned powerful spell.
Besides those, however, we also see creatures like the fae capable of performing feats of "magic" that dwarf anything we've seen humans do. Their abilities do not appear to be the same kind of magic that humans use, rather it's some sort of innate ability they have. In particular, I don't think we've ever seen a far tire after using their powers, and we've seen the Faerie Queens do impressive things (up to and including total control over the climate.) It appears that their power in the NeverNever is essentially unlimited, but even on Earth it's really strong.
Fortunately, the fae are constrained by their nature, meaning they are unlikely to run around willy-nilly doing massive magic spells. They generally stick to the things they know; most of the cases where we've seen a Faerie Queen flip out was when someone disrupted the natural course of things they they were responding to the threat.
Dresdenverse operates on a "Clap Your Hands If You Believe" style of magic. Belief creates truth (for mortals, anyway).
Whether that belief is in Magic itself, as Harry believes, or belief in the Divine, as Michael believes in his actions and duty as a Knight of the Cross, or any other belief, that is how supernatural effects are created.
To demonstrate the difference, the only thing preventing Harry from being atheist is that he's met archangels; Harry can't use a cross to ward off vampires. However, Harry's belief in magic does allow him to use his mother's pentacle (representative of the five Western classical elements, bound by human will) for a similar purpose, and Michael can use crosses to repel the creatures of the night.
Similarly, so many people believe in the "Shroud of Turin" held by the Vatican, it has power. But that is not the actual Shroud of Turin.
Supernatural creatures may operate slightly differently, in that they are born for a purpose and excel at that purpose; faeries and demons and so on may not even "believe" in things with the same sense that mortals do.
Although mortal magic has few-if-any theoretical limitations, it has practical limitations such as obtaining enough power to fuel a given spell, and skill to put the spell together.
Finally, the White Council of Wizards imposes a few more limitations on mortal practitioners. While the Laws of Magic don't prevent certain spells from being cast, someone who casts such spells invites a Warden's sword to a tea party with their neck. The Warlock's head is not invited.
- Thou Shalt Not Kill
(This only applies to killing with magic, not killing with mortal means; also, only killing "people" counts, and monsters like vampires and faeires aren't "people")
- Thou Shalt Not Transform Others
- Thou Shalt Not Invade the Mind of Another
- Thou Shalt Not Enthrall Another
- Thou Shalt Not Reach Beyond the Borders of Life
(This only technically applies to human corpses; making a zombie T-Rex toes the line without crossing it)
- Thou Shalt Not Swim Against the Currents of Time
(Even inspecting the future is frowned upon, although the Gatekeeper seems to be able and permitted to bend this rule)
- Thou Shalt Not Open the Outer Gates
(Also applies to the Outsiders from beyond the Outer Gates; even learning about the Outer Gates and the Outsiders can be punishable; naturally, the Gatekeeper is exempt, as guarding the Outer Gates is among his duties)
For all of the above Laws, the Wizard with the position of the Blackstaff is exempt.
There are no limits on magic itself.
The limitations come instead from how much one's body can endure. As Harry has said many times, magic is about preparation and/or being able to control the raw magic which you evoke. Instances are given many times of wizards who have attempted to evoke too much power in too short a time and killed themselves in the process.
If you wish to bring about great changes with magic, you either have to accomplish it over a very long period of time, with much research and planning, or you have to be able to endure your raw magic overwhelming you.
Fairies on the other hand have much more power and a greater and inherent control of it, but faeries are bound by other restrictions, particularly governing their interactions with the mortal world.
Yes, Dresden Files has limits to what it's magic can do. The broadest bit of this is that you can't use magic to make something happen unless you truly believe it should happen. You can't use magic to find your keys unless you truly believe your keys should be found. You can't use magic to throw a fireball unless you really believe that fire should be thrown. And you can't use magic to kill someone unless you truly believe they should be dead.
Most magic we see in Dresden is thaumatergy - forging a link between something big and something small. In one book, Harry uses this to create a detection web in a hotel - he takes a tub of play-dough and puts bits of it all over the hotel. He then uses the remainder in the tub and links them all together magically.
A villain from an earlier book used Black Magic (defined as magic which violates one of the White Council's Laws) thaumatergy to kill people at a distance - he had a piece of the person (in this case, bodily fluids and hair), powered a magical rite with feelings of lust, and used a thaumatergical connection between the person's bits and the person to forge a link between them and a small animal. He used that connection to rip their hearts out from across a city.
There's dozens more examples, but thaumatergy is the simplest type of magic for a mortal to use.
Evocation is another type of magic. It deals with moving and transforming energy. Harry is extremely skilled and has a natural talent for evocation. He can use it for several things, most notably his common spell: fuego. With this spell (or any of the variants) Harry conjures fire. He can throw fireballs, create pillars of flame, or any of a number of other uses. This doesn't come freely, though - the energy comes from somewhere. Sometimes it comes from within Harry, other times he channels it from the surrounding environment. Notably, he once used a massive fire spell to
Freeze part of a lake, creating a sheet of ice thick enough to support several people's weight so they could escape from a sinking ship. He channeled heat from the lake into the fire, causing the lake to partially freeze.
Magic can also be used to enhance things and make them more of what they already are. Leather is a tough material, and Harry famously has used magic to enhance his leather duster to the point where it can stop most bullets.
Potions are made in a similar way - take things which have a desired quality, mix them together and add magic to get a short-term magical effect. Using tequila, a large bill, ashes from a romance novel, and a few other things, Harry brews a 'love' potion at one point. It gives the drinker the feelings of love (or, given who helped him make it, lust).
Magic can also be used to summon things from the Never Never (or Beyond), to create illusions, to mess with people's minds, to heal, or any of a number of other uses.
In short, Dresden's magic is both more and less powerful than Harry Potter's. It can't be used (well) untrained, it doesn't require any tools or artifacts, and there's always a cost to what you get. That said, it can do lots of things Harry Potter's magic isn't shown to do. It can turn you truly invisible (not just Disillusioned), can control the winds and elements, can reverse gravity...but it takes a great deal of skill and training. You can't simply hand an 11-year-old a stick and watch magic happen.
I keep seeing references to Harry's use of fire, Harry is not an evoker, he is very limited in it's use, that's why he carries a blasting rod. Harry relies heavily on tools to focus magic from evocation school. Morgan from the wardens on the other hand is a true evoker and does not rely on such devices to cast such down and dirty raw magic as Harry puts it.
Harry is often quoted as saying >given enough time and couple items there's nothing a Wizard couldn't accomplish.
Fae operate at different rules than humans and they are not restricted from messing with time. they can stop people from aging they can manipulate doors to allow people to go foward and backwards in time etc.