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Last Thursdayism is the idea that the universe was created last Thursday. This would imply that the laws of physics were created last Thursday too. Doesn't that mean anything could have happened before Last Thursday, since there were no laws of physics? How can we predict where particles were before Last Thursday since there were no laws?

Or is it that, since the universe was created last Thursday to look 13.8 billion years old, it acts as if the laws of physics have been around for all those years?

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    And an evil demon deceiving us may mean that there are no particles, or us, right now. There is no limit to idle speculations, responding to them is a fool's errand. – Conifold Aug 19 at 5:06
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    The thing to get your mind around here is that physics, and science in general, does not study what is actual, it studies what is observable. So whether God made it last Thursday to look 13.8B old, or we are living in Bostrom's simulation, or Descartes' demon put our brains in a vat... All that is outside the scope of science. Science looks at the face value reality. – christo183 Aug 19 at 6:17
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    It is also possible that the universe is created anew in every moment and is evanescent, and this is a popular view. Thursdayism is ad hoc in physics, but it shows this possibility cannot be ruled out by sensory empiricism. – PeterJ Aug 19 at 13:07
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"Or is it that, since the universe was created last Thursday to look 13.8 billion years old, it acts as if the laws of physics have been around for all those years?"

Yeah, that's the idea. This is more of an epistemic thought experiment than a metaphysics one to be honest.

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When the universe was created last Thursday, it was created with a lot of interesting patterns for us to study.

We observe and gain understand those patterns, allowing us to predict things about those patterns we haven't seen. By coincidence (or design?!) those patterns have the same appearance as the way real-world objects behave today, so we can use what we know about those patterns to guide our expectations about real-world objects, and vice versa.

When we say where things were "last Wednesday", we don't claim anything 'actually existed' on that date — we're just referring to a particular the way those patterns looked on the day of creation.

In short, even if we took as an absolute axiom that the universe was created last Thursday, that has no effect on the actual form and practice of science, since what (ought to) matter to science is what we actually observe. At most, the lastthursdayism hypothesis might encourage us to search for irregularities dated on last Thursday.

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If the universe were created by some divine being with the appearance of age, it could in theory have been created with a kind of physics that can be observed to change. Maybe the speed of light wouldn't be constant for example.

But that's not the kind of physics we observe. So if a divine being created this universe with the appearance of age, with the physics we can study we would have to say that the physical processes and laws have continued unchanged in both real history and the created apparent history. If God created a single photon from nothing, we could not observe it being created, and could only deduce that it had been traveling in a straight line at constant speed. If God creates anything out of nothing apparent age/history is actually essential, because our scientific understanding has no capacity for the violation of the law of conservation of mass/energy.

A divine being could change physics in a discontinuous manner, however if that happened before we'd started observing the universe in a strict scientific manner we wouldn't be able to deduce now that it had ever occurred. Such a discontinuous change to the physical laws is essentially what a miracle is.

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Last Thursdayism is a criticism of the omphalos hypothesis created by Philip Henry Gosse in 1857. Wikipedia describes it as follows:

The omphalos hypothesis is one attempt to reconcile the scientific evidence that the universe is billions of years old with the Genesis creation narrative, which implies that the Earth is only a few thousand years old. It is based on the religious belief that the universe was created by a divine being, within the past ten thousand years (in keeping with flood geology), and that the presence of objective, verifiable evidence that the universe is older than approximately ten millennia is entirely due to the creator introducing false evidence that makes the universe appear much, much older.

Last Thursdayism is an attempt to criticize such a view of creation:

Though Gosse's original omphalos hypothesis specifies a popular creation story, others have proposed that the idea does not preclude creation as recently as five minutes ago, including memories of times before this created in situ. This idea is sometimes called Last Thursdayism by its opponents, as in "the world might as well have been created last Thursday."

Wikipedia also notes that Last Thursdayism is impossible to test scientifically:

The concept is both unverifiable and unfalsifiable through any conceivable scientific study—in other words, it is impossible even in principle to subject it to any form of test, by reference to any empirical data, because the empirical data themselves are considered to have been arbitrarily created to look the way they do at every observable level of detail.

Since there is nothing to observe and since Last Thursdayism does not originate from within physics itself (like the big bang), it requires no physical explanation any more than would Russell's teapot or the Flying Spaghetti Monster.

However, it does encourage skeptical questioning, perhaps unwittingly, about how real physical laws are. Are physical laws discoveries about nature as it really is or are they inventions of our minds that happen to work even if the universe has been around for billions of years?


Wikipedia contributors. (2019, August 4). Omphalos hypothesis. In Wikipedia, The Free Encyclopedia. Retrieved 14:57, August 19, 2019, from https://en.wikipedia.org/w/index.php?title=Omphalos_hypothesis&oldid=909247454

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