why is modern physics significant?

Answer 1

1. Nuclear power.
2. Wave-particle duality.
3. Big Bang

The Newtonian view of the Universe has been overthrown, supplanted by a relativistic view within which Newtonian physics is a special-case approximation.

Answer 2

There are a lot of reasons why modern physics is significant. If you ask a physicist, the most relevant, though least practical, answer is so that we can increase our knowledge. Humans are curious creatures, we always want more knowledge. All physics in its time is about understanding how the universe works. It's like looking into the mind of God. Though Newton's laws were good approximations, they're just not exactly right.

A thorough understanding of modern physics helps us to know where the entire universe began, and where it's going. It's heading towards letting us know exactly what we are made of, what the fundamental building blocks of the universe are.

Of slightly lesser importance is the engineering concepts put forth by it. Engineering on an atomic scale is impossible without understanding quantum mechanics. And engineering on a cosmic scale is impossible without understanding general relativity. Without these we wouldn't have such things as GPS or nuclear power.

In short, modern physics is significant because classical physics, to put it bluntly, is just wrong. We want understanding and answers, and modern physics is what's leading us there.

Answer 3

There are discoveries which will be made which will yield all sort of technological advancements as well as a new understanding of everyday occurance. Sometimes, this is not good because it opens a can of worms. E.g. Fusion physics made it possible to destroy Earth itself and create cancer, while at the same time it holds the possibility of providing vast amounts of energy.
When Maxwell was studying electricity and magnetism and The Wright Brothers trying powered human flight 100 years ago, many thought they were just quacks and hobbiests.

Answer 4

Jerry P has some good reasons and I will add to his list.

X-rays
MRI
semicondutors
computers
LCD's

All of these are other applications of modern physics that would not be possible without it.