I know next to nothing about physics, other than what I see on PBS or listening to Brian Green’s lectures on YouTube, but one thing seems constant, physicists are always searching for a way to united the forces in a unified theory.
This is my question, is there any reason why they all should be united? Is it possible that they are not ever going to be united, because they just aren’t that way.
I know this sounds dumb but I don’t know how else to ask it. So does physics need a unified theory? Or could it be they haven’t found one, because there isn’t one
Well, the basic problem is there comes a point where the very very small (Quantum Mechanics) doesn’t play nice with the very, very big (General Relativity).
Mostly, this is evident when it comes to gravity.
There’s an unshakable feeling, and indeed some promising theories that hope to eventually unify/reconcile these two major pieces that just don’t seem to jive quite yet. So, something is evidently missing.
The thing that sucks is, compared to electromagnetism, and the two nuclear forces, gravity is vastly weaker, so it takes a very large instrument to probe ever smaller into the whole dilemma. Which is what most of the ruckus at the LHC (at CERN) is all about (and the search for the predicted Higgs Boson).
Short answer: understanding the big bang and black holes and such, require a theory that both are very massive (so that relativity applies) and very small (so that quantum physics applies).
Long answer: wait for the physicists to come around.
As to “Does there need to be a unified theory”, this notion has mostly to do with uniting the fundamental forces of nature, which must all play together nice… somehow… we just haven’t quite unwound the huge tangled ball of christmas lights yet.
If you want to get really simple, not having a unified theory means that both of the current theories are somewhat wrong. Since science is ultimately about gaining correct knowledge of the world around us, it would be weird if we weren’t trying to fix the problem.
This is probably the best answer so far, but I suppose it depends on your definition of “need”. Most people don’t need to have the deepest possible understanding of how their toaster works, but some people are driven to take it apart and see the nuts and bolts, and other people are driven to learn about heat radiance, etc.
I suppose the most practical answer as to whether we will actually “need” a unified theory is whether we can make some real-world applications out of that understanding. There are lots of ideas out there regarding time travel, faster-than-light travel, inexhaustible energy supplies,etc., that suggest maybe maybe there are some. And it’s possible that our understanding will tell us some of those things aren’t possible and we can stop wasting our time one them (but of course lots of people won’t anyway). We can’t really know whether we need a unified theory in practical terms until we have one, and when we have it, the question becomes moot.
I think you are lacking a “feel” for what unified theories are all about. I’ll give you an example. A staggering number of otherwise seemingly unrelated laws and facts about the natural world, including but not limited to temperature, pressure, brownian motion, the different states of matter, latent heat of evaporation/fusion, crystallization, in fact all of chemistry, all are unified by a very simple idea: the atomic theory of matter. Before so many phenomena seemed completely whimsical; separate unrelated models had to be built to describe each one, predictions were often wrong, and models were perilously hacked-together to try to fit the results of new experiments; the world seemed very complicated indeed! But all of that – almost everything about the world we see around us, in fact – can be derived from, and explained by, the fact that the world is composed of little things called atoms. The unifying concept then allows new predictions to be made that can be tested (ie we can do science). Unification isn’t just some aesthetic preference; it is the mechanism by which physics moves forward. Do you think that, before we had thought of atoms, we should have been content with our understanding of the world? After all, after doing enough experiments we could have come up with all sorts of complicated equations that seemed to give more or less the right answer regarding pressure, temperature, and so on, without ever really understanding why they worked the way they did. We are in much the same position today as we were before we thought of atoms: we have models for how different things work, but those models don’t fit together very well, and we don’t understand why those models are the way they are. A unifying theory would explain the different models as being the result of some more fundamental thing, allowing us to fit everything together and understand why they are the way they are.
One reason I have always given for the remarkable level of support that some governments, especially the US government, have given to fundamental physics is that they still remember the last time a bunch of physicists came running in with a whole new set of theories about how the universe worked. They had a whole lot of crazy ideas about relativity, quantum physics, and all sorts of particles inside atoms. From Rutherford in 1911 and Einstein’s work in 1905 to Einstein writing to Roosesvelt in 1939 was only 3 decades. That letter was of course describing the practicality of an atomic weapon. In 1911 Rutherford discovered that the atom had a nucleus, and in 1905 Einstein had published his initial work on relativity.
One might also cynically suggest that some of the support for experimental high energy physics has waned as it has become more apparent that whilst there are very likely new things to be found, and new physics to be uncovered, it isn’t going to be within the reach of a just compressing the heck out of lump of metal to get a really big bang.
It is possible that unification won’t ever be achieved, but others have pointed out how our current theories seem to work at very large and very small scales, but they don’t integrate well. We don’t know what happens when you have something both large and small (such as a black hole, for one).
However, unification has been a very common theme throughout science, so I think it’s realistic to expect unification in more areas. More often than not, we’ve taken very complicated things, discovered a few common building blocks and then we can see how the array of complicated things result from the simple building blocks. Alchemy was a mess; chemistry understood that a hundred elements combined to make everything. Nuclear physics showed that those hundred elements are composed of just three types of subatomic particles. When we discovered hundreds of subatomic particles, we discovered things like quarks so that only a dozen components could once again explain hundreds of results.
As for usefulness, just look at one of the first unifications: electromagnetism. It’s one thing to know that electrical fields exist and that magnetic fields exist. It’s another to realize that an electrical current produces a magnetic field and that a moving magnetic field produces an electrical current. Without that knowledge, you don’t get electrical power generation on a massive scale or electric motors.
The thing is, you usually don’t know what’s useful until after you discover the connection. To attempt to answer a question like “Is antigravity possible?” will probably require a unified theory.
I should note that the OP is asking about unified field theories, not necessarily the Theory of Everything. There are other forces than gravity, and one might reasonably ask whether the Electroweak Force must necessarily be unifiable with the Strong Force. For that matter, a reconciliation of General Relativity with Quantum Mechanics needn’t necessarily unify gravity with the other forces, either: The String Model hopes to do so, but Loop Quantum Gravity (which really, is about as promising as the String Model) doesn’t include that feature.
So to answer the question the OP actually asked, instead of the question everyone else wanted to answer: No, a unified theory is not actually necessary. We do have some experimental hints that suggest that the electroweak and strong forces can be unified, and electroweak theory itself is the result of a successful unification of the electromagnetic and weak forces. If the electroweak and strong forces could be unified, it would simplify and extend our understanding of fundamental physics, and fundamental physicists generally have a sense that simpler theories are closer to the truth. In any event, though, there’s little reason beyond wishful thinking to believe that GR can be unified with the other forces, even if it can be reconciled with them.
I realize this was just an off-the-cuff example, but I don’t see this really being true. You’d need a valid theory of gravity (e.g., the proven existence of the graviton) in order to figure out how to negate it to anti-gravity, but it doesn’t necessarily have to be unified with the other forces.