So now you're saying that at least Newton's Second Law was not derived from anything; do I understand that right?
Nope. I'll say it again.
neither F=ma nor Einstein's postulate of constant c arose out of nowhere--they were based upon observations of the real world
So they were derived from observations of the natural world. Which is the case for all theories. And "Law" is merely an obsolete term for a simple theory that was once thought to be absolutely correct.
I disagree with this last statement. When things are moving slowly relative to the speed of light, and gravity isn't "too" strong, there is no difference between Newton's and Einstein's versions of things. Newton's Laws are not contradicted in these circumstances; they describe things perfectly to any precision you care to measure with (because all measurements are finite, and any differences are tiny).
I disagree. Anytime there is motion or gravity, Newton's and Einstein's equations yield different predictions. Whether or not those differences are within the range of a practical measurement is irrelevant. There are therefore only two possibilities: Only one of them is correct (i.e. exactly accurate) as a description of reality or neither of them is correct. I don't think that it is semantics to insist that "correct" and "true" mean only one thing: an absolutely perfect description of reality to an infinite degree of precision. So a theory cannot be "true" at one time, and not true at a later time. I think talking about degrees of truth when it comes to reality makes about as much since as being a little bit pregnant. We have plenty of perfectly good terms for talking about theories that are close, but not absolutely correct under every conceivable condition--"approximation" for example. I agree that pretty much all of physics is approximation, but that is no excuse for abandoning the concept of truth. Let's preserve the conventional meanings of truth as "absolute and perfect correspondence to reality."
I'm trying to make two points here. First of all, Einstein's stuff and Newton's stuff are the same at low energies (low speed, low gravity), because all the scary looking bits become zero at low energy to any precision you care to measure at. They predict the same behaviour. They work the same. They look the same. They are the same.
There is nothing about the equations of either theory that limits it to a particular range of conditions. A true theory must yield perfectly valid results for any physically realistic value of its parameters. If it fails to do so, then it is merely approximation to the true (and quite possibly unknown) theory.
Really? Which principles? We were always told that, for example, F=ma is simply given; that's just what happens. Everything else is built up from that. (It's sort of an axiom.)
Derived from basic mathematical principles means derived mathematically from simple axioms, like F = ma. But of course, neither F=ma nor Einstein's postulate of constant c arose out of nowhere--they were based upon observations of the real world.
Actually, Roger Penrose proved that every black hole has a singularity in 1964. It's called, unsurprisingly, the Singularity Theorem [wolfram.com].
Remember that every proof is of the form,
IF premises THEN conclusions.
So a proof may be mathematically valid, but it is scientifically true (i.e. a correct description of the real world) only if the premises are true. The premises of Penrose's proof were General Relativity. Since there is good reason to believe that GR cannot be universally correct, particularly at the infinitesimal distance scale of a singularity, Penrose's conclusions cannot be presumed to be true for the real world.
They were not "incorrect"... they merely fail to describe all reality, as does every other theory we have.
Since the goal of a scientific theory is to describe reality, a theory is "correct" if it accurately describes reality, and incorrect if it does not. A theory cannot, of course, be proved to be correct--it can only be proved incorrect, by obtaining a reliable experimental result that contradicts the predictions of the theory. So, practically speaking, theories fall into two classes: those that have been shown to be incorrect, such as Newton's Laws of Motion, and those that have not yet been shown to be incorrect, and thus still have some chance (although probably only a small one) of being correct.
A theory may be incorrect, but still useful as an approximation. So, for example, Newton's and Einstein's theories of gravity are both considered to be incorrect--Newton's because it is contradicted by experiment, and Einstein's because it yields implausible results when applied at very small scales of distance, but Einstein's is a better approximation--i.e. it yields predictions that are closer to the experimentally determined values than Newton's.
Facts are boring things, because they are all just single observations. Here's an example of a fact: On October 15, 2002, I dropped a pencil. It accelerated toward the ground and stopped on impact.
Theories are a lot more interesting, because they are the generalizations that tie facts together. Here are a couple of examples of theories:
"A dropped objects falls toward the center of the earth"
"There is a universal force attracting particles of matter together that is proportional to mass and inversely proportional to the square of the separation of their centers of mass."
Basically, everything that we think we know about the universe is a theory.
I recently heard an interesting description of the difference between a "Law" and a "Theory": a "law" is purely observational, whereas a "theory" implies some understanding of what's going on underneath things; a theory is derived from more basic principles. Newton's Laws of Motion, and Kepler's Laws of Orbit, are based on observations (fits, basically), although they might have had at least some idea of why it might be that way. Einstein's Theory of Relativity is derived from the ground up starting from some basic principles (I think you can get most (all?) of it from assuming the speed of light is a constant for all inertial reference frames!).
Unfortunately, it is sheer nonsense. Newton's "Laws" of Motion are derived from basic mathematical premises, just like Einstein's theory of relativity. And of course, theories are ultimately intended to explain observation, whether they are empirical or derived from mathematical postulates
A more accurate explanation is: "Law" is an obsolete term for a simple, widely accepted theory. These days, science changes fast enough that theories almost never get referred to as "laws". One consequence of that is that most of the scientific "laws" are now known to be false. For example, Newton's Laws of Motion are incorrect, and have been superseded by the theory of special relativity
Comets can orbit the sun for a really long time; some smack into an object (like the sun, for instance), some escape their orbit, and some just keep orbiting. There's nothing that guarantees the star will get sucked in; it all depends on the orbital path, really. It may experience a slingshot effect and leave the black hole altogether.
According to current theory, on a long enough time scale, no orbits are stable, because the orbital energy is radiated away as gravitational waves. So everything that orbits a black hole falls into it eventually. In a continuously expanding universe, pretty much all of the matter ultimately ends up in black holes. As the universe continues to expand, all of the blackholes become unstable, as the blackbody temperature of the universe falls below their surface temperatures. They then "evaporate" by radiation. What happens to their singularities is, AFAIK, still a matter of debate. So ultimately, you end up with a universe with nothing in it but photons, and maybe some naked singularities.
True, but current theories also haven't proven that inside a black hole _is_ a singularity
Since we have no unified theory, it is not possible to prove anything mathematically with confidence. The current theory of gravitation, Einstein's general relativity, requires a singularity. But GR is presumed not to be valid at quantum scales of distance, and since a singularity is infinitely small in GR, all bets are off.
People who have sex where there is a high chance of contracting AIDS aren't following ANY evolutionary guidelines: AIDS causes death, which puts a hamper on your ability to breed, AIDS also kill your mate, putting a hamper on his/her ability to procreate, AIDS can infect the child, causing, again, death. Just what rules is any person following by risking AIDS?
It's not a matter of following "evolutionary rules." Instincts are blind, thoughtless drives, burned into the nervous system by millions of years of evolution. The drive to reproduce evolutionarily predates the capacity for thought.
And remember, AIDS is a new disease. Perhaps after a thousand years and millions of deaths, AIDS will lead to an evolutionary modification of the drive to procreate. The hard fact is that while individuals can sometimes be persuaded or forced to limit their reproductive activity, nobody anywhere has ever met with real success in enforcing strict monogamy. Expecting to eliminate AIDS by persuading most of the people on earth to be strictly monogamous is living in a fantasy world.
Sorry i lost my mom to cancer, so i get a little annoyed when i see lots of money getting spent on developing a cure for a disease that is avoidible. Instead of on horrible random disease like cancer. To the mods sorry for the off topic post.
I lost my wife to cancer, but that's no excuse for this kind of idiocy.
a) Some cancer is avoidable (e.g. smoking) and some AIDS is not (transfusion, maternal transmission to infants).
b) Expecting people to avoid a disease by resisting the single most powerful biological instinct is stupid. It isn't going to happen. A medical treatment is the only hope.
c) HIV is a wake-up call. It is purely our good fortune that it is so hard to get that you have to have sex or a transfusion to get it, rather than being spread by mosquitoes like West Nile, or through the air like measles. The next virus to come down the pike may not be so well-behaved as HIV. Most of what we learn fighting HIV is likely to help us against the next one.
d) It's not a zero-sum game. Advances in biology are often portable. A cure for cancer could quite plausibly come out of AIDS research.
e) AIDS is increasing; most cancers are not. We don't have to worry about an epidemic of cancer among young people. Yet just such an AIDS epidemic is wiping out people wholesale in Africa. There is so much sickness that it is contributing to starvation, because people are too ill to raise food.
As a biologist and pharmacologist, I run folding@home myself. But realistically, I think its chance of curing cancer or AIDS is about as good as SETI@home's chance of finding aliens.
Apple has never supported changing basic interface elements. I've had many utilities that tweaked basic elements of Apple's OS6-9. Many of them broke with major operating system upgrades, because they used undocumented or unsupported hooks. It doesn't seem like much has changed.
I don't think anybody understands genetic algorithms all that well. GA's are based upon guesses about which aspects of genetic organization and recombination are critical for evolution. Considering that our understanding of genetic organization, mutation, and recombination is very incomplete, it is hardly surprising that our clumsy atempts to emulate the system don't work all that well. After all, modern organisms are the ones that *did* evolve--which means that they have undergone selection for evolution. There are all sorts of questions: the importance of introns and gene duplication, the role of epigenetic mechansims, etc.
The argument that our genetic algorithms don't work well enough to explain evolution is a bit like arguing that our airplanes don't maneuver as well as a hummingbird, so hummingbird flight must not be explainable by aerodynamics.
I've looked as some of Spetner's stuff, and his definition of "information" is obvious nonsense, and clearly designed to give him the "answer" that he's looking for.
I put it in the category of "theft of services." It is generally accepted that the concept of theft need not entail actual loss by the victim--it is the act of taking/using something, physical or not, that you have no right to without the permission of the person who does have the right to it. For example, it is still car theft if I take your car without permission while you are on vacation, drive it around, and return it, fully gassed, exactly where you left it.
Generally, if people leave useful stuff out on the sidewalk, the default assumption--barring notification to the contrary--is "free to all."
I don't see how an unsecured network is any different. It is so easy to add password or other simple security that it is reasonable to presume that anybody offering network access to the neighborhood intends to do so. Of course, simple courtesy demands that one not abuse such a service--by sending out 10,0000 spams, for example.
On the other hand, it is certainly theft to break into the network, no matter how rudimentary the security.
Once a bug (defined as a failure or a program to function as documented, advertised, or otherwise represented by the publisher) is reported to the developer, the publisher must
1) Within 6 weeks, acknowledge the bug by posting the information on a web site or sending the information to registered users via postal or email.
2) Within 6 months, contact all registered users and either a) offer a full refund of the purchase price, or b) provide a fixed version of the program.
Failure to comply with these requirements renders any exclusion of consequential damages related to the bug in question invalid.
25% sounds about right to me as an estimate of the "it ain't broke I ain't gonna fix it" group. Consider that you are a long-time Mac user. You have all of the applications you need, you know the system well, everything is working fine. You just need one more machine for a new employee. Why should you switch? You don't care if OSX is better--better or worse, it's still different, and everybody would have to learn it. Not everybody is a computer enthusiast. A lot of people will keep doing what they have been doing until there is a strong reason to switch--a must-have application that requires OSX, or a decision to upgrade to a newer computer that no longer boots into 9.
If Apple does not include functionality to use OS7/8/9 apps in OSX, then it will hurt them.
Undoubtedly. Fortunately, there are no plans to do this. You don't have to boot into OS9 to use OS7/8/9 apps in OSX. As when Apple switched to PowerPC, they included a backwards compatibility mode right from the outset. I have plenty of legacy applications. Fortunately, they all run fine under Classic mode in OSX.
This seems less of a problem than when Apple dropped the serial and Desktop bus ports. I expect that there are quite a few people holding onto an older Mac because they have peripherals or software dongles that require these ports. And I'm sure that there will be rare applications that don't work under Classic mode--probably about as many as failed when Apple went from System 6 to 7, or 8 to 9. Fortunately, keeping your old Mac is a perfectly adequate solution--those old Macs works as well as ever, and they can share data with the newer systems via the network.
The part about not using MDI style applications is in my opinion _very_ wrong. I often have 3 or more applications open when working and I find it damn confusing to look at all of them at the same time. Ever hit something outside the program you are working in and then spend time finding your way back?
This is really something that depends upon whether your generally work in one program, or are always switching between programs. Apple really should have made this a System Preference. I use a shareware utility called ASM, which allows user control of this behavior.
I still can't stand the default position of the dock at the bottom of the screen. It doesn't go well with windws that resize from the bottom-right corner, or with horizontal scroll bars.
But I understand why Apple put it there. Windows has a lot of people conditioned to look to the bottom of the screen for an application menu/launcher. Similarly, the great big icons make it hard to miss for the new user.
Fortunately, they also included a lot of customization. I am much more comfortable with the dock since I stuck it to the right side of my screen, reduced its size way down, and turned the magnification down. And to my suprise, I find that those high-res icons still look good, and remain recognizable when reduced to the same size as the old small icons.
This is a common misunderstanding. It wouldn't matter if it was only one pixel. It means millions of color choices, not millions of colors simultaneously. For truly high-quality color, you need more colors available than even the entire screen is able to display simultaneously.
If a user doesn't have the dexterity to aim without thinking about it, he or she shouldn't be using a computer, or perhaps even driving or using public restrooms. I'm serious.
It's not a matter of consciously thinking about it. Even if it goes on at a subconscious level, hitting a particular point takes more cerebral processing time than simply snapping to an edge. In fact, it is the unconscious nature of the processing that makes it insidious--because we aren't aware of "aiming," we don't perceive how much it slows us down, although objective tests show it.
In todays world, with optical mice, 21" LCD displays, multiple monitors, and mouse acceleration, the parameters would be different, and there may no longer be an advantage for edge menus.
Nope. Still works. Even with the largest monitors, Apple's mouse acceleration parameters are such that a flick of the wrist puts the pointer instantly in the menubar from anywhere on the screen.
Slashdot Mirror
Nope. I'll say it again.
So they were derived from observations of the natural world. Which is the case for all theories. And "Law" is merely an obsolete term for a simple theory that was once thought to be absolutely correct.I disagree. Anytime there is motion or gravity, Newton's and Einstein's equations yield different predictions. Whether or not those differences are within the range of a practical measurement is irrelevant. There are therefore only two possibilities: Only one of them is correct (i.e. exactly accurate) as a description of reality or neither of them is correct. I don't think that it is semantics to insist that "correct" and "true" mean only one thing: an absolutely perfect description of reality to an infinite degree of precision. So a theory cannot be "true" at one time, and not true at a later time. I think talking about degrees of truth when it comes to reality makes about as much since as being a little bit pregnant. We have plenty of perfectly good terms for talking about theories that are close, but not absolutely correct under every conceivable condition--"approximation" for example. I agree that pretty much all of physics is approximation, but that is no excuse for abandoning the concept of truth. Let's preserve the conventional meanings of truth as "absolute and perfect correspondence to reality."
I'm trying to make two points here. First of all, Einstein's stuff and Newton's stuff are the same at low energies (low speed, low gravity), because all the scary looking bits become zero at low energy to any precision you care to measure at. They predict the same behaviour. They work the same. They look the same. They are the same.
There is nothing about the equations of either theory that limits it to a particular range of conditions. A true theory must yield perfectly valid results for any physically realistic value of its parameters. If it fails to do so, then it is merely approximation to the true (and quite possibly unknown) theory.
Derived from basic mathematical principles means derived mathematically from simple axioms, like F = ma. But of course, neither F=ma nor Einstein's postulate of constant c arose out of nowhere--they were based upon observations of the real world.
Remember that every proof is of the form,
IF premises THEN conclusions.
So a proof may be mathematically valid, but it is scientifically true (i.e. a correct description of the real world) only if the premises are true. The premises of Penrose's proof were General Relativity. Since there is good reason to believe that GR cannot be universally correct, particularly at the infinitesimal distance scale of a singularity, Penrose's conclusions cannot be presumed to be true for the real world.
Since the goal of a scientific theory is to describe reality, a theory is "correct" if it accurately describes reality, and incorrect if it does not. A theory cannot, of course, be proved to be correct--it can only be proved incorrect, by obtaining a reliable experimental result that contradicts the predictions of the theory. So, practically speaking, theories fall into two classes: those that have been shown to be incorrect, such as Newton's Laws of Motion, and those that have not yet been shown to be incorrect, and thus still have some chance (although probably only a small one) of being correct.
A theory may be incorrect, but still useful as an approximation. So, for example, Newton's and Einstein's theories of gravity are both considered to be incorrect--Newton's because it is contradicted by experiment, and Einstein's because it yields implausible results when applied at very small scales of distance, but Einstein's is a better approximation--i.e. it yields predictions that are closer to the experimentally determined values than Newton's.
Facts are boring things, because they are all just single observations. Here's an example of a fact: On October 15, 2002, I dropped a pencil. It accelerated toward the ground and stopped on impact.
Theories are a lot more interesting, because they are the generalizations that tie facts together. Here are a couple of examples of theories:
"A dropped objects falls toward the center of the earth"
"There is a universal force attracting particles of matter together that is proportional to mass and inversely proportional to the square of the separation of their centers of mass."
Basically, everything that we think we know about the universe is a theory.
Unfortunately, it is sheer nonsense. Newton's "Laws" of Motion are derived from basic mathematical premises, just like Einstein's theory of relativity. And of course, theories are ultimately intended to explain observation, whether they are empirical or derived from mathematical postulates
A more accurate explanation is: "Law" is an obsolete term for a simple, widely accepted theory. These days, science changes fast enough that theories almost never get referred to as "laws". One consequence of that is that most of the scientific "laws" are now known to be false. For example, Newton's Laws of Motion are incorrect, and have been superseded by the theory of special relativity
According to current theory, on a long enough time scale, no orbits are stable, because the orbital energy is radiated away as gravitational waves. So everything that orbits a black hole falls into it eventually. In a continuously expanding universe, pretty much all of the matter ultimately ends up in black holes. As the universe continues to expand, all of the blackholes become unstable, as the blackbody temperature of the universe falls below their surface temperatures. They then "evaporate" by radiation. What happens to their singularities is, AFAIK, still a matter of debate. So ultimately, you end up with a universe with nothing in it but photons, and maybe some naked singularities.
Since we have no unified theory, it is not possible to prove anything mathematically with confidence. The current theory of gravitation, Einstein's general relativity, requires a singularity. But GR is presumed not to be valid at quantum scales of distance, and since a singularity is infinitely small in GR, all bets are off.
It's not a matter of following "evolutionary rules." Instincts are blind, thoughtless drives, burned into the nervous system by millions of years of evolution. The drive to reproduce evolutionarily predates the capacity for thought.
And remember, AIDS is a new disease. Perhaps after a thousand years and millions of deaths, AIDS will lead to an evolutionary modification of the drive to procreate. The hard fact is that while individuals can sometimes be persuaded or forced to limit their reproductive activity, nobody anywhere has ever met with real success in enforcing strict monogamy. Expecting to eliminate AIDS by persuading most of the people on earth to be strictly monogamous is living in a fantasy world.
I lost my wife to cancer, but that's no excuse for this kind of idiocy.
a) Some cancer is avoidable (e.g. smoking) and some AIDS is not (transfusion, maternal transmission to infants).
b) Expecting people to avoid a disease by resisting the single most powerful biological instinct is stupid. It isn't going to happen. A medical treatment is the only hope.
c) HIV is a wake-up call. It is purely our good fortune that it is so hard to get that you have to have sex or a transfusion to get it, rather than being spread by mosquitoes like West Nile, or through the air like measles. The next virus to come down the pike may not be so well-behaved as HIV. Most of what we learn fighting HIV is likely to help us against the next one.
d) It's not a zero-sum game. Advances in biology are often portable. A cure for cancer could quite plausibly come out of AIDS research.
e) AIDS is increasing; most cancers are not. We don't have to worry about an epidemic of cancer among young people. Yet just such an AIDS epidemic is wiping out people wholesale in Africa. There is so much sickness that it is contributing to starvation, because people are too ill to raise food.
As a biologist and pharmacologist, I run folding@home myself. But realistically, I think its chance of curing cancer or AIDS is about as good as SETI@home's chance of finding aliens.
You can bet that the ones who couldn't figure out TiVo are not the ones that are going to be using their PCs or XBox's as PVRs.
Apple has never supported changing basic interface elements. I've had many utilities that tweaked basic elements of Apple's OS6-9. Many of them broke with major operating system upgrades, because they used undocumented or unsupported hooks. It doesn't seem like much has changed.
I don't think anybody understands genetic algorithms all that well. GA's are based upon guesses about which aspects of genetic organization and recombination are critical for evolution. Considering that our understanding of genetic organization, mutation, and recombination is very incomplete, it is hardly surprising that our clumsy atempts to emulate the system don't work all that well. After all, modern organisms are the ones that *did* evolve--which means that they have undergone selection for evolution. There are all sorts of questions: the importance of introns and gene duplication, the role of epigenetic mechansims, etc.
The argument that our genetic algorithms don't work well enough to explain evolution is a bit like arguing that our airplanes don't maneuver as well as a hummingbird, so hummingbird flight must not be explainable by aerodynamics.
I've looked as some of Spetner's stuff, and his definition of "information" is obvious nonsense, and clearly designed to give him the "answer" that he's looking for.
I put it in the category of "theft of services." It is generally accepted that the concept of theft need not entail actual loss by the victim--it is the act of taking/using something, physical or not, that you have no right to without the permission of the person who does have the right to it. For example, it is still car theft if I take your car without permission while you are on vacation, drive it around, and return it, fully gassed, exactly where you left it.
Generally, if people leave useful stuff out on the sidewalk, the default assumption--barring notification to the contrary--is "free to all."
I don't see how an unsecured network is any different. It is so easy to add password or other simple security that it is reasonable to presume that anybody offering network access to the neighborhood intends to do so. Of course, simple courtesy demands that one not abuse such a service--by sending out 10,0000 spams, for example.
On the other hand, it is certainly theft to break into the network, no matter how rudimentary the security.
Once a bug (defined as a failure or a program to function as documented, advertised, or otherwise represented by the publisher) is reported to the developer, the publisher must
1) Within 6 weeks, acknowledge the bug by posting the information on a web site or sending the information to registered users via postal or email.
2) Within 6 months, contact all registered users and either a) offer a full refund of the purchase price, or b) provide a fixed version of the program.
Failure to comply with these requirements renders any exclusion of consequential damages related to the bug in question invalid.
25% sounds about right to me as an estimate of the "it ain't broke I ain't gonna fix it" group. Consider that you are a long-time Mac user. You have all of the applications you need, you know the system well, everything is working fine. You just need one more machine for a new employee. Why should you switch? You don't care if OSX is better--better or worse, it's still different, and everybody would have to learn it. Not everybody is a computer enthusiast. A lot of people will keep doing what they have been doing until there is a strong reason to switch--a must-have application that requires OSX, or a decision to upgrade to a newer computer that no longer boots into 9.
Undoubtedly. Fortunately, there are no plans to do this. You don't have to boot into OS9 to use OS7/8/9 apps in OSX. As when Apple switched to PowerPC, they included a backwards compatibility mode right from the outset. I have plenty of legacy applications. Fortunately, they all run fine under Classic mode in OSX.
This seems less of a problem than when Apple dropped the serial and Desktop bus ports. I expect that there are quite a few people holding onto an older Mac because they have peripherals or software dongles that require these ports. And I'm sure that there will be rare applications that don't work under Classic mode--probably about as many as failed when Apple went from System 6 to 7, or 8 to 9. Fortunately, keeping your old Mac is a perfectly adequate solution--those old Macs works as well as ever, and they can share data with the newer systems via the network.
This is really something that depends upon whether your generally work in one program, or are always switching between programs. Apple really should have made this a System Preference. I use a shareware utility called ASM, which allows user control of this behavior.
I still can't stand the default position of the dock at the bottom of the screen. It doesn't go well with windws that resize from the bottom-right corner, or with horizontal scroll bars.
But I understand why Apple put it there. Windows has a lot of people conditioned to look to the bottom of the screen for an application menu/launcher. Similarly, the great big icons make it hard to miss for the new user.
Fortunately, they also included a lot of customization. I am much more comfortable with the dock since I stuck it to the right side of my screen, reduced its size way down, and turned the magnification down. And to my suprise, I find that those high-res icons still look good, and remain recognizable when reduced to the same size as the old small icons.
This is a common misunderstanding. It wouldn't matter if it was only one pixel. It means millions of color choices, not millions of colors simultaneously. For truly high-quality color, you need more colors available than even the entire screen is able to display simultaneously.
It's not a matter of consciously thinking about it. Even if it goes on at a subconscious level, hitting a particular point takes more cerebral processing time than simply snapping to an edge. In fact, it is the unconscious nature of the processing that makes it insidious--because we aren't aware of "aiming," we don't perceive how much it slows us down, although objective tests show it.
Nope. Still works. Even with the largest monitors, Apple's mouse acceleration parameters are such that a flick of the wrist puts the pointer instantly in the menubar from anywhere on the screen.