Griffon

You do not to have to go into physics of course after your degree. What else interests you? For example I understand the financial sectors still look for bright graduates in theoretical physics and mathematics.

 

Most of the theorists I have known have been part of experimental research groups and by and large not in those areas we normally associate with theoretical physics like cosmology, particle physics and so on. They have been theorists in atomic physics, condensed matter physics, laser physics and so on.

 

So it's far from true that theorists only work at the edges of physics in fields like string theory. Theorists bring very necessary skills in mathematical techniques, computing and understand the underlying physics to an experimental research group. The theorists very often set the direction of the research too.

 

So, in your position I might look at what areas are currently topical and being funded in your country. Discover which are the most successful research groups. Maybe apply to do a PhD with a theoretical bias in one of those successful groups. Also think about the areas of physics that interest you apart from the standard ones you've mentioned.

I'm not that keen on faith education. I'd rather children were taught to be rational, to think and to question.

 

But I have to say that fundamentalist secularists worry me too. I'd rather live in a society that was tolerant of different ways of life, which includes parental freedom to choose how their children are educated.

I understand your argument. I am taking the viewpoint that there may be something extraordinarily fortuitous about emergence of life, or of intelligent life, that knowledge we acquire in millenias time could lead us to understand we are unique without visiting all environs. I doubt we are unique, but believe it is too early to say.

Yes. I see what you mean. In such circumstances I might imagine we could say the possibility of life elsewhere was vanishingly small, in a finite universe anyway. But we could never be certain that somewhere in a galaxy far far away life like ours had also developed.

 

I also find such a scenario depressingly bleak.

That looks like an Argument from Ignorance. Just because you cannot see how we might determine this does not mean it is not possible.

It depends what it is we are saying. I was taking the OP's question "What if aliens didn't exist?" to mean just that: didn't exist anywhere. I can't see how we could know that for sure. We might be able to say they don't exist in a more limited sense, within our solar system say, or even further afield eventually. We could indeed be the first intelligent species to populate the galaxy.

What's your interest, Petrushka?

Interesting question. I know a fair bit about lasers and almost nothing about masers apart from their use as atomic clocks, communications, radar etc. I suppose the most obvious difference is wavelength. Lasers cover the near IR to x-Ray region of the EMS whilst masers are in the microwave region.

I can't see how we could possibly know there were no intelligent extraterrestrial life forms apart from ourselves. We would have to have explored the whole universe to know that.

 

In the very distant future we might be able to conclude that there are no detectable technologically capable alien civilisations in our galaxy. If this turns out to be true it would indicate just how rare are civilisations like our own - and profoundly influence our view of ourselves as a species.

In fact, how can they reasonably be called "truths" if they are not subject to investigation or even falsification?

Quite.

 

My last sentence woud have been better put the other way around.

 

I can think of few things more closed minded than accepting "miracles, omens, etc." as truths.

I pick up on the following sentence.

 

"Many things are not explainable by the conventional scientific logic which does not accept many truths like miracles, omens, etc and tries to answer every question with not a very open view."

L

I can think of few things more closed minded than accepting the truths of "miracles, omens, etc."

Wouldn't the two masses have to start accelerating towards one another from an infinite distance apart?

 

I'm imagining a universe consisting only of two equal masses set initially at some distance apart.

A theory is false with just one experiment the contrary.

 

It would be a contradiction in terms to say it should be possible in principle to find observations showing a theory to be untrue, and at the same time saying a theory is true. Indeed, if such were the case, the world would be chaotic.

 

A so called supernatural explanation is a falsification.

I'm not sure what you're saying exactly.

 

I agree a theory can be shown to be false by experimental result.

 

My point is that not all explanations can be shown to be false. For such explanations there is no observation or experiment you can make that can show the explanation to be false. The theory that an undetectable goblin moves my car keys about so I cant find them is such an explanation. [if only I could catch the blighter though!]

 

Such explanations are unscientific. For an explanation to be described as scientific it must be possible, in principle, to show that it is false. The discovery that neutrinos travelled faster than the speed of light would have been sufficient to falsify relativity as it stands. That's what's meant by "falsifiable".

I see what you're saying. But doesn't string theory make predictions that we can't test, and won't be able to test if ever because of the inaccessible energies required. Mind you, I suppose the same might be said of theoretical considerations of the conditions at the earliest time within the Big Bang. I suppose all we can do when experiments are not possible is to see how well the theory predicts what we see now.

I think you have to include journalists in the blame for that, possibly more than the scientists.

True. So perhaps scientists should be more careful.

 

So, should string theory be considered a scientific theory? Lee Smollin has his doubts. Perhaps it's a branch of mathematics?

 

PS How odd. I keep trying to add this comment on ST as separate post, but it keeps adding it to this post. Doesn't this forum allow you to post twice in a row?

You have to explain to the level of your audience. But when you don't know that level, you have to guess. We never got any feedback that we were talking above or were at Vay's level.

Yes, that is true. Although the level of the question is an indication of a sort.

Again "everything which "begins to exist" has a cause apart from itself. The Christian God never began to exist! You can't make up your own god and apply your gods limitations to mine!!

Yeah, you're postulating an eternal entity. There's nothing in the cosmological argument that self evidently points to the existence of such an entity, let alone that it is what you call the Christian God. The arguments just don't stack up.

 

PS is it really so bad not knowing the true origins of the universe?

To Crispy Bacon ...

 

Why doesn't your "everything" include God? Why is God the special entity that needs no point of creation?

 

And if you admit the possibility of the existence of a prime cause that had no cause, why can't that cause be the universe itself rather than a supernatural entity?

Yes, we can be sloppy, because of the mixing of the lay use and scientific use of the word in discussions. However, I would argue that a physicist is in a much better position to discern between the two definitions when s/he hears it from another physicist, than from a layperson who doesn't know the difference, or that there is a difference. The problem is in communicating to a lay audience and being sloppy, and the main problem there lies in a lack of training or practice in communicating with a lay audience.

Yes. I think that's because working physicists are pragmatists and don't worry too much about what the word theory actually means. They use the term theory to cover everything from a speculative explanation, with maybe a smattering of supporting evidence, to relativity, which has been tested till the pips squeak. I don't think this is good enough. Many so called new "theories" that get reported to fill column inches of New Scientist or Scientific American are actually not theories with anything like the stature of Darwin's theory of the evolution of species, say, or the atomic theory of matter. We might term them somthing like proto-theories.

We can't read that article ...

 

Interesting that you say Karl Popper has fallen out of favour. I'd heard that of late. I'm not sure why, or why Ruse is critical of him. Popper was generally highly thought of when I started out in science 35 yeas ago.

Yes. Oh how many times have I found myself arguing with some creationist or whatever who comes out with the famous 'but it's just a theory'? It doesn't seem to matter how patiently you try and explain the difference between a scientific theory and every day use of the word .... they often don't want to understand the difference.

I experience something like this from time to time. It's a bit like there's a big stationary lorry up road with its engine idling. The frequency is just too low to hear. I sort of feel it. Odd.

 

I also hear it intermittently in pubs too. No funny comments please! But I put that down to some kind of pump perhaps. But it tends to go on for sometime, 20 minutes perhaps. Then I'm aware it's stopped.

 

It's quite unpleasant in fact. Almost like my head is being pummelled.

 

Mind you, I'm increasingly getting tinnitus too as I get older. Most of the time I just ignore it.

Swansont - exactly. Though many have been persuaded by the cosmological argument down the centuries. The fallacy is contained in the assertion that everything has a cause.

Am I alone in thinking that many physicists are sloppy in their use if the word theory? As we've seen a scientific theory has quite a tight definition. Yet the word theory is often used to describe explanations weakly supported by evidence, such as some recent theories in cosmology, to the pillars of modern physics like quantum theory and relativity. In part I think this is why 'theory' has such a bad reputation in non-scientific circles. Hypothesis might be a better word, or maybe we need something between a hypothesis and a theory?

Some nice explanations so far.

 

I would add that a scientific theory should be falsifiable. It should be possible in principle to find an observation that shows the theory to be untrue. That doesn't mean the theory is false.

 

Some explanations are not falsifiable in any known way, like supernatural explanations for example, so are not scientific.

"If you know calculus" ... that's the nub isn't it! It moves the mysterious appearance of one half to somewhere else i.e. the integration of the variable v being v^2/2

 

I had the experience a few years ago of trying to explain this to a young person who was confused about this very issue. I too came at it from the mathematical end, which is entirely natural to me. Nevertheless we weren't making any headway and I realised that the maths was obscuring rather than revealing. It's often not helpful to explain something using explanations that are at least if not more complicated, especially for people who are not mathematically inclined. It turned out that we had to go back to basics and explain things which my young tutee had forgotten or not taken in. Things like work done is defined as the force applied in moving (or accelerating) an object over a certain distance, the equivalance of potential and kinetic energy, Newton's second law, the equations of motion etc. No calculus was involved. We got there!

I don't see an answer to Vay's question. He is an elementary physics student who needs the big picture. Vay asks a reasonable question: where does the 1/2 come from? He probably won't understand an explanation expressed with unfamiliar symbols and variables. Relativity theory is probably not familiar either.

I agree with you. I sometimes wonder whether there's an element of 'look how clever I am' in answers on science boards. Ajb's answer was about the right level I'd have thought. And now there are a range of answers which, if the OP is willing to spend time on them, he should be able to glean an understanding at several levels.

 

Regarding the fact that KE is proportional to velocity squared, I have long felt this to be unintuitive. You might naively expect that doubling the velocity would provide an object with twice the energy rather than four times. But that is just the way it is from the definitions of Work (force x distance) and Newton's second law (Force = mass x acceleration), as contained in ajb's simple explanation.